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DOCS - Bring doc improvements for v3 across from master (#2593)
* Docs: some work on the network map docs. * Address review comments * Address review comments * Docs: discuss zone constraints, flow drains and more upgrade related topics (#2585) Docs: discuss zone constraints, flow drains and more upgrade related topics.
This commit is contained in:
Mike Hearn
Katelyn Baker
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f4a9a055d9
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9be6022012
@ -7,55 +7,135 @@ API: Contract Constraints
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Contract constraints
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--------------------
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Transaction states specify a constraint over the contract that will be used to verify it. For a transaction to be
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valid, the ``verify`` function associated with each state must run successfully. However, for this to be secure, it is
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not sufficient to specify the ``verify`` function by name as there may exist multiple different implementations with
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the same method signature and enclosing class. Contract constraints solve this problem by allowing a contract developer
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to constrain which ``verify`` functions out of the universe of implementations can be used (i.e. the universe is
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everything that matches the signature and contract constraints restrict this universe to a subset).
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A typical constraint is the hash of the CorDapp JAR that contains the contract and states but will in future releases
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include constraints that require specific signers of the JAR, or both the signer and the hash. Constraints can be
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specified when constructing a transaction; if unspecified, an automatic constraint is used.
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Corda separates verification of states from their definition. Whilst you might have expected the ``ContractState``
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interface to define a verify method, or perhaps to do verification logic in the constructor, instead it is primarily
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done by a method on a ``Contract`` class. This is because what we're actually checking is the
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validity of a *transaction*, which is more than just whether the individual states are internally consistent.
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The transition between two valid states may be invalid, if the rules of the application are not being respected.
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For instance, two cash states of $100 and $200 may both be internally valid, but replacing the first with the second
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isn't allowed unless you're a cash issuer - otherwise you could print money for free.
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For a transaction to be valid, the ``verify`` function associated with each state must run successfully. However,
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for this to be secure, it is not sufficient to specify the ``verify`` function by name as there may exist multiple
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different implementations with the same method signature and enclosing class. This normally will happen as applications
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evolve, but could also happen maliciously.
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Contract constraints solve this problem by allowing a contract developer to constrain which ``verify`` functions out of
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the universe of implementations can be used (i.e. the universe is everything that matches the signature and contract
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constraints restrict this universe to a subset). Constraints are satisfied by attachments (JARs). You are not allowed to
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attach two JARs that both define the same application due to the *no overlap rule*. This rule specifies that two
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attachment JARs may not provide the same file path. If they do, the transaction is considered invalid. Because each
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state specifies both a constraint over attachments *and* a Contract class name to use, the specified class must appear
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in only one attachment.
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So who picks the attachment to use? It is chosen by the creator of the transaction that has to satisfy input constraints.
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The transaction creator also gets to pick the constraints used by any output states, but the contract logic itself may
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have opinions about what those constraints are - a typical contract would require that the constraints are propagated,
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that is, the contract will not just enforce the validity of the next transaction that uses a state, but *all successive
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transactions as well*. The constraints mechanism creates a balance of power between the creator of data on
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the ledger and the user who is trying to edit it, which can be very useful when managing upgrades to Corda applications.
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There are two ways of handling upgrades to a smart contract in Corda:
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1. *Implicit:* By allowing multiple implementations of the contract ahead of time, using constraints.
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2. *Explicit:* By creating a special *contract upgrade transaction* and getting all participants of a state to sign it using the
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contract upgrade flows.
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This article focuses on the first approach. To learn about the second please see :doc:`upgrading-cordapps`.
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The advantage of pre-authorising upgrades using constraints is that you don't need the heavyweight process of creating
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upgrade transactions for every state on the ledger. The disadvantage is that you place more faith in third parties,
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who could potentially change the app in ways you did not expect or agree with. The advantage of using the explicit
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upgrade approach is that you can upgrade states regardless of their constraint, including in cases where you didn't
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anticipate a need to do so. But it requires everyone to sign, requires everyone to manually authorise the upgrade,
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consumes notary and ledger resources, and is just in general more complex.
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How constraints work
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--------------------
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Starting from Corda 3 there are two types of constraint that can be used: hash and zone whitelist. In future
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releases a third type will be added, the signature constraint.
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**Hash constraints.** The behaviour provided by public blockchain systems like Bitcoin and Ethereum is that once data is placed on the ledger,
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the program that controls it is fixed and cannot be changed. There is no support for upgrades at all. This implements a
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form of "code is law", assuming you trust the community of that blockchain to not release a new version of the platform
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that invalidates or changes the meaning of your program.
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This is supported by Corda using a hash constraint. This specifies exactly one hash of a CorDapp JAR that contains the
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contract and states any consuming transaction is allowed to use. Once such a state is created, other nodes will only
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accept a transaction if it uses that exact JAR file as an attachment. By implication, any bugs in the contract code
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or state definitions cannot be fixed except by using an explicit upgrade process via ``ContractUpgradeFlow``.
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.. note:: Corda does not support any way to create states that can never be upgraded at all, but the same effect can be
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obtained by using a hash constraint and then simply refusing to agree to any explicit upgrades. Hash
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constraints put you in control by requiring an explicit agreement to any upgrade.
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**Zone constraints.** Often a hash constraint will be too restrictive. You do want the ability to upgrade an app,
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and you don't mind the upgrade taking effect "just in time" when a transaction happens to be required for other business
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reasons. In this case you can use a zone constraint. This specifies that the network parameters of a compatibility zone
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(see :doc:`network-map`) is expected to contain a map of class name to hashes of JARs that are allowed to provide that
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class. The process for upgrading an app then involves asking the zone operator to add the hash of your new JAR to the
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parameters file, and trigger the network parameters upgrade process. This involves each node operator running a shell
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command to accept the new parameters file and then restarting the node. Node owners who do not restart their node in
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time effectively stop being a part of the network.
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**Signature constraints.** These are not yet supported, but once implemented they will allow a state to require a JAR
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signed by a specified identity, via the regular Java jarsigner tool. This will be the most flexible type
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and the smoothest to deploy: no restarts or contract upgrade transactions are needed.
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**Defaults.** The default constraint type is either a zone constraint, if the network parameters in effect when the
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transaction is built contain an entry for that contract class, or a hash constraint if not.
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A ``TransactionState`` has a ``constraint`` field that represents that state's attachment constraint. When a party
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constructs a ``TransactionState`` without specifying the constraint parameter a default value
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(``AutomaticHashConstraint``) is used. This default will be automatically resolved to a specific
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``HashAttachmentConstraint`` that contains the hash of the attachment which contains the contract of that
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``TransactionState``. This automatic resolution occurs when a ``TransactionBuilder`` is converted to a
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``WireTransaction``. This reduces the boilerplate involved in finding a specific hash constraint when building a
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transaction.
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constructs a ``TransactionState``, or adds a state using ``TransactionBuilder.addOutput(ContractState)`` without
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specifying the constraint parameter, a default value (``AutomaticHashConstraint``) is used. This default will be
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automatically resolved to a specific ``HashAttachmentConstraint`` or a ``WhitelistedByZoneAttachmentConstraint``.
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This automatic resolution occurs when a ``TransactionBuilder`` is converted to a ``WireTransaction``. This reduces
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the boilerplate that would otherwise be involved.
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It is possible to specify the constraint explicitly with any other class that implements the ``AttachmentConstraint``
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interface. To specify a hash manually the ``HashAttachmentConstraint`` can be used and to not provide any constraint
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the ``AlwaysAcceptAttachmentConstraint`` can be used - though this is intended for testing only. An example below
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shows how to construct a ``TransactionState`` with an explicitly specified hash constraint from within a flow:
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Finally, an ``AlwaysAcceptAttachmentConstraint`` can be used which accepts anything, though this is intended for
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testing only.
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Please note that the ``AttachmentConstraint`` interface is marked as ``@DoNotImplement``. You are not allowed to write
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new constraint types. Only the platform may implement this interface. If you tried, other nodes would not understand
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your constraint type and your transaction would not verify.
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.. warning:: An AlwaysAccept constraint is effectively the same as disabling security for those states entirely.
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Nothing stops you using this constraint in production, but that degrades Corda to being effectively a form
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of distributed messaging with optional contract logic being useful only to catch mistakes, rather than potentially
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malicious action. If you are deploying an app for which malicious actors aren't in your threat model, using an
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AlwaysAccept constraint might simplify things operationally.
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An example below shows how to construct a ``TransactionState`` with an explicitly specified hash constraint from within
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a flow:
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.. sourcecode:: java
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// Constructing a transaction with a custom hash constraint on a state
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TransactionBuilder tx = new TransactionBuilder()
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TransactionBuilder tx = new TransactionBuilder();
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Party notaryParty = ... // a notary party
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DummyState contractState = new DummyState()
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SecureHash myAttachmentsHash = serviceHub.cordappProvider.getContractAttachmentID(DummyContract.PROGRAM_ID)
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TransactionState transactionState = new TransactionState(contractState, DummyContract.Companion.getPROGRAMID(), notaryParty, new AttachmentHashConstraint(myAttachmentsHash))
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DummyState contractState = new DummyState();
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tx.addOutputState(transactionState)
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WireTransaction wtx = tx.toWireTransaction(serviceHub) // This is where an automatic constraint would be resolved
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LedgerTransaction ltx = wtx.toLedgerTransaction(serviceHub)
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ltx.verify() // Verifies both the attachment constraints and contracts
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SecureHash myAttachmentHash = SecureHash.parse("2b4042aed7e0e39d312c4c477dca1d96ec5a878ddcfd5583251a8367edbd4a5f");
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TransactionState transactionState = new TransactionState(contractState, DummyContract.Companion.getPROGRAMID(), notaryParty, new AttachmentHashConstraint(myAttachmentHash));
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This mechanism exists both for integrity and security reasons. It is important not to verify against the wrong contract,
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which could happen if the wrong version of the contract is attached. More importantly when resolving transaction chains
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there will, in a future release, be attachments loaded from the network into the attachment sandbox that are used
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to verify the transaction chain. Ensuring the attachment used is the correct one ensures that the verification is
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tamper-proof by providing a fake contract.
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tx.addOutputState(transactionState);
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WireTransaction wtx = tx.toWireTransaction(serviceHub); // This is where an automatic constraint would be resolved.
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LedgerTransaction ltx = wtx.toLedgerTransaction(serviceHub);
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ltx.verify(); // Verifies both the attachment constraints and contracts
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Hard-coding the hash of your app in the code itself can be pretty awkward, so the API also offers the ``AutomaticHashConstraint``.
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This isn't a real constraint that will appear in a transaction: it acts as a marker to the ``TransactionBuilder`` that
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you require the hash of the node's installed app which supplies the specified contract to be used. In practice, when using
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hash constraints, you almost always want "whatever the current code is" and not a hard-coded hash. So this automatic
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constraint placeholder is useful.
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CorDapps as attachments
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-----------------------
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CorDapp JARs (:doc:`cordapp-overview`) that are installed to the node and contain classes implementing the ``Contract``
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CorDapp JARs (see :doc:`cordapp-overview`) that are installed to the node and contain classes implementing the ``Contract``
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interface are automatically loaded into the ``AttachmentStorage`` of a node at startup.
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After CorDapps are loaded into the attachment store the node creates a link between contract classes and the attachment
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@ -63,28 +143,12 @@ that they were loaded from. This makes it possible to find the attachment for an
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automatic resolution of attachments is done by the ``TransactionBuilder`` and how, when verifying the constraints and
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contracts, attachments are associated with their respective contracts.
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Implementations of AttachmentConstraint
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---------------------------------------
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There are three implementations of ``AttachmentConstraint`` with more planned in the future.
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``AlwaysAcceptAttachmentConstraint``: Any attachment (except a missing one) will satisfy this constraint.
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``AutomaticHashConstraint``: This will be resolved to a ``HashAttachmentConstraint`` when a ``TransactionBuilder`` is
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converted to a ``WireTransaction``. The ``HashAttachmentConstraint`` will include the attachment hash of the CorDapp
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that contains the ``ContractState`` on the ``TransactionState.contract`` field.
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``HashAttachmentConstraint``: Will require that the hash of the attachment containing the contract matches the hash
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stored in the constraint.
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We plan to add a future ``AttachmentConstraint`` that will only be satisfied by the presence of signatures on the
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attachment JAR. This allows for trusting of attachments from trusted entities.
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Limitations
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-----------
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An ``AttachmentConstraint`` is verified by running the ``AttachmentConstraint.isSatisfiedBy`` method. When this is called
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it is provided only the relevant attachment by the transaction that is verifying it.
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.. note:: The obvious way to write a CorDapp is to put all you states, contracts, flows and support code into a single
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Java module. This will work but it will effectively publish your entire app onto the ledger. That has two problems:
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(1) it is inefficient, and (2) it means changes to your flows or other parts of the app will be seen by the ledger
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as a "new app", which may end up requiring essentially unnecessary upgrade procedures. It's better to split your
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app into multiple modules: one which contains just states, contracts and core data types. And another which contains
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the rest of the app. See :ref:`cordapp-structure`.
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Testing
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-------
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@ -93,7 +157,8 @@ Since all tests involving transactions now require attachments it is also requir
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for tests. Unit test environments in JVM ecosystems tend to use class directories rather than JARs, and so CorDapp JARs
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typically aren't built for testing. Requiring this would add significant complexity to the build systems of Corda
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and CorDapps, so the test suite has a set of convenient functions to generate CorDapps from package names or
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to specify JAR URLs in the case that the CorDapp(s) involved in testing already exist.
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to specify JAR URLs in the case that the CorDapp(s) involved in testing already exist. You can also just use
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``AlwaysAcceptAttachmentConstraint`` in your tests to disable the constraints mechanism.
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MockNetwork/MockNode
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********************
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@ -102,12 +167,14 @@ The simplest way to ensure that a vanilla instance of a MockNode generates the c
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``cordappPackages`` constructor parameter (Kotlin) or the ``setCordappPackages`` method on ``MockNetworkParameters`` (Java)
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when creating the MockNetwork. This will cause the ``AbstractNode`` to use the named packages as sources for CorDapps. All files
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within those packages will be zipped into a JAR and added to the attachment store and loaded as CorDapps by the
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``CordappLoader``. An example of this usage would be:
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``CordappLoader``.
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An example of this usage would be:
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.. sourcecode:: java
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class SomeTestClass {
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MockNetwork network = null
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MockNetwork network = null;
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@Before
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void setup() {
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@ -117,6 +184,7 @@ within those packages will be zipped into a JAR and added to the attachment stor
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... // Your tests go here
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}
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MockServices
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************
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@ -127,6 +195,10 @@ to use as CorDapps using the ``cordappPackages`` parameter.
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MockServices mockServices = new MockServices(Arrays.asList("com.domain.cordapp"))
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However - there is an easier way! If your unit tests are in the same package as the contract code itself, then you
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can use the no-args constructor of ``MockServices``. The package to be scanned for CorDapps will be the same as the
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the package of the class that constructed the object. This is a convenient default.
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Driver
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******
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@ -1,14 +1,25 @@
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Network Map
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===========
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The network map is a collection of signed ``NodeInfo`` objects (signed by the node it represents and thus tamper-proof)
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forming the set of reachable nodes in a compatibility zone. A node can receive these objects from two sources:
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The network map is a collection of signed ``NodeInfo`` objects. Each NodeInfo is signed by the node it represents and
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thus cannot be tampered with. It forms the set of reachable nodes in a compatibility zone. A node can receive these
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objects from two sources:
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1. The HTTP network map service if the ``compatibilityZoneURL`` config key is specified.
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1. A network map server that speaks a simple HTTP based protocol.
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2. The ``additional-node-infos`` directory within the node's directory.
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HTTP network map service
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------------------------
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The network map server also distributes the parameters file that define values for various settings that all nodes need
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to agree on to remain in sync.
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.. note:: In Corda 3 no implementation of the HTTP network map server is provided. This is because the details of how
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a compatibility zone manages its membership (the databases, ticketing workflows, HSM hardware etc) is expected to vary
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between operators, so we provide a simple REST based protocol for uploading/downloading NodeInfos and managing
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network parameters. A future version of Corda may provide a simple "stub" implementation for running test zones.
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In Corda 3 the right way to run a test network is through distribution of the relevant files via your own mechanisms.
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We provide a tool to automate the bulk of this task (see below).
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HTTP network map protocol
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-------------------------
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If the node is configured with the ``compatibilityZoneURL`` config then it first uploads its own signed ``NodeInfo``
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to the server (and each time it changes on startup) and then proceeds to download the entire network map. The network map
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@ -31,6 +42,12 @@ The set of REST end-points for the network map service are as follows.
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| GET | /network-map/network-parameters/{hash} | Retrieve the signed network parameters (see below). The entire object is signed with the network map certificate which is also attached. |
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+----------------+-----------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------+
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HTTP is used for the network map service instead of Corda's own AMQP based peer to peer messaging protocol to
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enable the server to be placed behind caching content delivery networks like Cloudflare, Akamai, Amazon Cloudfront and so on.
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By using industrial HTTP cache networks the map server can be shielded from DoS attacks more effectively. Additionally,
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for the case of distributing small files that rarely change, HTTP is a well understood and optimised protocol. Corda's
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own protocol is designed for complex multi-way conversations between authenticated identities using signed binary
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messages separated into parallel and nested flows, which isn't necessary for network map distribution.
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The ``additional-node-infos`` directory
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---------------------------------------
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@ -43,24 +60,39 @@ latest one is taken.
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On startup the node generates its own signed node info file, filename of the format ``nodeInfo-${hash}``. To create a simple
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network without the HTTP network map service then simply place this file in the ``additional-node-infos`` directory
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of every node that's part of this network.
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of every node that's part of this network. For example, a simple way to do this is to use rsync.
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Usually, test networks have a structure that is known ahead of time. For the creation of such networks we provide a
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``network-bootstrapper`` tool. This tool pre-generates node configuration directories if given the IP addresses/domain
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names of each machine in the network. The generated node directories contain the NodeInfos for every other node on
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the network, along with the network parameters file and identity certificates. Generated nodes do not need to all be
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online at once - an offline node that isn't being interacted with doesn't impact the network in any way. So a test
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cluster generated like this can be sized for the maximum size you may need, and then scaled up and down as necessary.
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More information can be found in :doc:`setting-up-a-corda-network`.
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Network parameters
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------------------
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Network parameters are a set of values that every node participating in the zone needs to agree on and use to
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correctly interoperate with each other. If the node is using the HTTP network map service then on first startup it will
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download the signed network parameters, cache it in a ``network-parameters`` file and apply them on the node.
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correctly interoperate with each other. They can be thought of as an encapsulation of all aspects of a Corda deployment
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on which reasonable people may disagree. Whilst other blockchain/DLT systems typically require a source code fork to
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alter various constants (like the total number of coins in a cryptocurrency, port numbers to use etc), in Corda we
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have refactored these sorts of decisions out into a separate file and allow "zone operators" to make decisions about
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them. The operator signs a data structure that contains the values and they are distributed along with the network map.
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Tools are provided to gain user opt-in consent to a new version of the parameters and ensure everyone switches to them
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at the same time.
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If the node is using the HTTP network map service then on first startup it will download the signed network parameters,
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cache it in a ``network-parameters`` file and apply them on the node.
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.. warning:: If the ``network-parameters`` file is changed and no longer matches what the network map service is advertising
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then the node will automatically shutdown. Resolution to this is to delete the incorrect file and restart the node so
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that the parameters can be downloaded again.
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.. note:: A future release will support the notion of phased rollout of network parameter changes.
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If the node isn't using a HTTP network map service then it's expected the signed file is provided by some other means.
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For such a scenario there is the network bootstrapper tool which in addition to generating the network parameters file
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also distributes the node info files to the node directories. More information can be found in :doc:`setting-up-a-corda-network`.
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also distributes the node info files to the node directories.
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The current set of network parameters:
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@ -92,16 +124,23 @@ Network parameters update process
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---------------------------------
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In case of the need to change network parameters Corda zone operator will start the update process. There are many reasons
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that may lead to this decision: we discovered that some new fields have to be added to enable smooth network interoperability or change
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of the existing compatibility constants is required due to upgrade or security reasons.
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that may lead to this decision: adding a notary, setting new fields that were added to enable smooth network interoperability,
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or a change of the existing compatibility constants is required, for example.
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To synchronize all nodes in the compatibility zone to use the new set of the network parameters two RPC methods exist. The process
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requires human interaction and approval of the change.
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.. note:: A future release may support the notion of phased rollout of network parameter changes.
|
||||
|
||||
To synchronize all nodes in the compatibility zone to use the new set of the network parameters two RPC methods are
|
||||
provided. The process requires human interaction and approval of the change, so node operators can review the
|
||||
differences before agreeing to them.
|
||||
|
||||
When the update is about to happen the network map service starts to advertise the additional information with the usual network map
|
||||
data. It includes new network parameters hash, description of the change and the update deadline. Node queries network map server
|
||||
for the new set of parameters and emits ``ParametersUpdateInfo`` via ``CordaRPCOps::networkParametersFeed`` method to inform
|
||||
node operator about the event.
|
||||
data. It includes new network parameters hash, description of the change and the update deadline. Nodes query the network map server
|
||||
for the new set of parameters.
|
||||
|
||||
The fact a new set of parameters is being advertised shows up in the node logs with the message
|
||||
"Downloaded new network parameters", and programs connected via RPC can receive ``ParametersUpdateInfo`` by using
|
||||
the ``CordaRPCOps.networkParametersFeed`` method. Typically a zone operator would also email node operators to let them
|
||||
know about the details of the impending change, along with the justification, how to object, deadlines and so on.
|
||||
|
||||
.. container:: codeset
|
||||
|
||||
@ -110,12 +149,22 @@ node operator about the event.
|
||||
:start-after: DOCSTART 1
|
||||
:end-before: DOCEND 1
|
||||
|
||||
Node administrator can review the change and decide if is going to accept it. The approval should be done before ``updateDeadline``.
|
||||
Nodes that don't approve before the deadline will be removed from the network map.
|
||||
If the network operator starts advertising a different set of new parameters then that new set overrides the previous set. Only the latest update can be accepted.
|
||||
To send back parameters approval to the zone operator RPC method ``fun acceptNewNetworkParameters(parametersHash: SecureHash)``
|
||||
has to be called with ``parametersHash`` from update. Notice that the process cannot be undone.
|
||||
The node administrator can review the change and decide if they are going to accept it. The approval should be do
|
||||
before the update Deadline. Nodes that don't approve before the deadline will likely be removed from the network map by
|
||||
the zone operator, but that is a decision that is left to the operator's discretion. For example the operator might also
|
||||
choose to change the deadline instead.
|
||||
|
||||
If the network operator starts advertising a different set of new parameters then that new set overrides the previous set.
|
||||
Only the latest update can be accepted.
|
||||
|
||||
To send back parameters approval to the zone operator, the RPC method ``fun acceptNewNetworkParameters(parametersHash: SecureHash)``
|
||||
has to be called with ``parametersHash`` from the update. Note that approval cannot be undone. You can do this via the Corda
|
||||
shell (see :doc:`shell`):
|
||||
|
||||
``run acceptNewNetworkParameters parametersHash: "ba19fc1b9e9c1c7cbea712efda5f78b53ae4e5d123c89d02c9da44ec50e9c17d"``
|
||||
|
||||
If the administrator does not accept the update then next time the node polls network map after the deadline, the
|
||||
advertised network parameters will be the updated ones. The previous set of parameters will no longer be valid.
|
||||
At this point the node will automatically shutdown and will require the node operator to bring it back again.
|
||||
|
||||
|
||||
Next time the node polls network map after the deadline the advertised network parameters will be the updated ones. Previous set
|
||||
of parameters will no longer be valid. At this point the node will automatically shutdown and will require the node operator
|
||||
to bring it back again.
|
||||
|
||||
@ -48,9 +48,6 @@ The ``version`` property, which defaults to 1, specifies the flow's version. Thi
|
||||
whenever there is a release of a flow which has changes that are not backwards-compatible. A non-backwards compatible
|
||||
change is one that changes the interface of the flow.
|
||||
|
||||
Currently, CorDapp developers have to explicitly write logic to handle these flow version numbers. In the future,
|
||||
however, the platform will use prescribed rules for handling versions.
|
||||
|
||||
What defines the interface of a flow?
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
The flow interface is defined by the sequence of ``send`` and ``receive`` calls between an ``InitiatingFlow`` and an
|
||||
@ -103,28 +100,19 @@ following behaviour:
|
||||
|
||||
How do I upgrade my flows?
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
For flag-day upgrades, the process is simple.
|
||||
|
||||
Assumptions
|
||||
^^^^^^^^^^^
|
||||
|
||||
* All nodes in the business network can be shut down for a period of time
|
||||
* All nodes retire the old flows and adopt the new flows at the same time
|
||||
|
||||
Process
|
||||
^^^^^^^
|
||||
|
||||
1. Update the flow and test the changes. Increment the flow version number in the ``InitiatingFlow`` annotation
|
||||
1. Update the flow and test the changes. Increment the flow version number in the ``InitiatingFlow`` annotation.
|
||||
2. Ensure that all versions of the existing flow have finished running and there are no pending ``SchedulableFlows`` on
|
||||
any of the nodes on the business network
|
||||
3. Shut down all the nodes
|
||||
4. Replace the existing CorDapp JAR with the CorDapp JAR containing the new flow
|
||||
5. Start the nodes
|
||||
any of the nodes on the business network. This can be done by *draining the node* (see below).
|
||||
3. Shut down the node.
|
||||
4. Replace the existing CorDapp JAR with the CorDapp JAR containing the new flow.
|
||||
5. Start the node.
|
||||
|
||||
From this point onwards, all the nodes will be using the updated flows.
|
||||
If you shut down all nodes and upgrade them all at the same time, any incompatible change can be made.
|
||||
|
||||
In situations where some nodes may still be using previous versions of a flow, the updated flows need to be
|
||||
backwards-compatible.
|
||||
In situations where some nodes may still be using previous versions of a flow and thus new versions of your flow may
|
||||
talk to old versions, the updated flows need to be backwards-compatible. This will be the case for almost any real
|
||||
deployment in which you cannot easily coordinate the rollout of new code across the network.
|
||||
|
||||
How do I ensure flow backwards-compatibility?
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
@ -262,37 +250,57 @@ In code, inlined subflows appear as regular ``FlowLogic`` instances without eith
|
||||
Inlined flows are not versioned, as they inherit the version of their parent ``InitiatingFlow`` or ``InitiatedBy``
|
||||
flow.
|
||||
|
||||
Are there any other considerations?
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Suspended flows
|
||||
^^^^^^^^^^^^^^^
|
||||
Currently, serialised flow state machines persisted in the node's database cannot be updated. All flows must finish
|
||||
before the updated flow classes are added to the node's plugins folder.
|
||||
|
||||
Flows that don't create sessions
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
Flows which are not an ``InitiatingFlow`` or ``InitiatedBy`` flow, or inlined subflows that are not called from an
|
||||
``InitiatingFlow`` or ``InitiatedBy`` flow, can be updated without consideration of backwards-compatibility. Flows of
|
||||
this type include utility flows for querying the vault and flows for reaching out to external systems.
|
||||
|
||||
Flow drains
|
||||
~~~~~~~~~~~
|
||||
|
||||
A flow *checkpoint* is a serialised snapshot of the flow's stack frames and any objects reachable from the stack.
|
||||
Checkpoints are saved to the database automatically when a flow suspends or resumes, which typically happens when
|
||||
sending or receiving messages. A flow may be replayed from the last checkpoint if the node restarts. Automatic
|
||||
checkpointing is an unusual feature of Corda and significantly helps developers write reliable code that can survive
|
||||
node restarts and crashes. It also assists with scaling up, as flows that are waiting for a response can be flushed
|
||||
from memory.
|
||||
|
||||
However, this means that restoring an old checkpoint to a new version of a flow may cause resume failures. For example
|
||||
if you remove a local variable from a method that previously had one, then the flow engine won't be able to figure out
|
||||
where to put the stored value of the variable.
|
||||
|
||||
For this reason, in currently released versions of Corda you must *drain the node* before doing an app upgrade that
|
||||
changes ``@Suspendable`` code. A drain blocks new flows from starting but allows existing flows to finish. Thus once
|
||||
a drain is complete there should be no outstanding checkpoints or running flows. Upgrading the app will then succeed.
|
||||
|
||||
A node can be drained or undrained via RPC using the ``setFlowsDrainingModeEnabled`` method, and via the shell using
|
||||
the standard ``run`` command to invoke the RPC. See :doc:`shell` to learn more.
|
||||
|
||||
Contract and state versioning
|
||||
-----------------------------
|
||||
Contracts and states can be upgraded if and only if all of the state's participants agree to the proposed upgrade. The
|
||||
following combinations of upgrades are possible:
|
||||
|
||||
* A contract is upgraded while the state definition remains the same
|
||||
* A state is upgraded while the contract stays the same
|
||||
* The state and the contract are updated simultaneously
|
||||
There are two types of contract/state upgrade:
|
||||
|
||||
1. *Implicit:* By allowing multiple implementations of the contract ahead of time, using constraints. See :doc:`api-contract-constraints` to learn more.
|
||||
2. *Explicit:* By creating a special *contract upgrade transaction* and getting all participants of a state to sign it using the
|
||||
contract upgrade flows.
|
||||
|
||||
This section of the documentation focuses only on the *explicit* type of upgrade.
|
||||
|
||||
In an explicit upgrade contracts and states can be changed in arbitrary ways, if and only if all of the state'
|
||||
s participants agree to the proposed upgrade. The following combinations of upgrades are possible:
|
||||
|
||||
* A contract is upgraded while the state definition remains the same.
|
||||
* A state is upgraded while the contract stays the same.
|
||||
* The state and the contract are updated simultaneously.
|
||||
|
||||
The procedure for updating a state or a contract using a flag-day approach is quite simple:
|
||||
|
||||
* Update and test the state or contract
|
||||
* Stop all the nodes on the business network
|
||||
* Produce a new CorDapp JAR file and distribute it to all the relevant parties
|
||||
* Start all nodes on the network
|
||||
* Run the contract upgrade authorisation flow for each state that requires updating on every node
|
||||
* For each state, one node should run the contract upgrade initiation flow
|
||||
* Update and test the state or contract.
|
||||
* Produce a new CorDapp JAR file and distribute it to all the relevant parties.
|
||||
* Each node operator stops their node, replaces the existing JAR with the new one, and restarts. They may wish to do
|
||||
a node drain first to avoid the definition of states or contracts changing whilst a flow is in progress.
|
||||
* Run the contract upgrade authorisation flow for each state that requires updating on every node.
|
||||
* For each state, one node should run the contract upgrade initiation flow, which will contact the rest.
|
||||
|
||||
Update Process
|
||||
~~~~~~~~~~~~~~
|
||||
|
||||
@ -26,6 +26,8 @@ For testing purposes, CorDapps may also include:
|
||||
In production, a production-ready webserver should be used, and these files should be moved into a different module or
|
||||
project so that they do not bloat the CorDapp at build time.
|
||||
|
||||
.. _cordapp-structure:
|
||||
|
||||
Structure
|
||||
---------
|
||||
You should base the structure of your project on the Java or Kotlin templates:
|
||||
|
||||
Loading…
Reference in New Issue
Block a user