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96 lines
3.7 KiB
ReStructuredText
96 lines
3.7 KiB
ReStructuredText
Nodes
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=====
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.. topic:: Summary
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* *A node is JVM run-time with a unique network identity running the Corda software*
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* *The node has two interfaces with the outside world:*
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* *A network layer, for interacting with other nodes*
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* *RPC, for interacting with the node's owner*
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* *The node's functionality is extended by installing CorDapps in the plugin registry*
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.. only:: htmlmode
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Video
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-----
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.. raw:: html
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<p><a href="https://vimeo.com/214168860">Corda Node, CorDapps and Network</a></p>
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<iframe src="https://player.vimeo.com/video/214168860" width="640" height="360" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe>
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<p></p>
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Node architecture
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-----------------
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A Corda node is a JVM run-time environment with a unique identity on the network that hosts Corda services and
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CorDapps.
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We can visualize the node's internal architecture as follows:
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.. image:: resources/node-architecture.png
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:scale: 25%
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:align: center
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The core elements of the architecture are:
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* A persistence layer for storing data
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* A network interface for interacting with other nodes
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* An RPC interface for interacting with the node's owner
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* A service hub for allowing the node's flows to call upon the node's other services
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* A cordapp interface and provider for extending the node by installing CorDapps
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Persistence layer
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-----------------
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The persistence layer has two parts:
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* The **vault**, where the node stores any relevant current and historic states
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* The **storage service**, where it stores transactions, attachments and flow checkpoints
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The node's owner can query the node's storage using the RPC interface (see below).
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Network interface
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-----------------
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All communication with other nodes on the network is handled by the node itself, as part of running a flow. The
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node's owner does not interact with other network nodes directly.
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RPC interface
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-------------
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The node's owner interacts with the node via remote procedure calls (RPC). The key RPC operations the node exposes
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are documented in :doc:`api-rpc`.
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The service hub
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---------------
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Internally, the node has access to a rich set of services that are used during flow execution to coordinate ledger
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updates. The key services provided are:
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* Information on other nodes on the network and the services they offer
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* Access to the contents of the vault and the storage service
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* Access to, and generation of, the node's public-private keypairs
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* Information about the node itself
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* The current time, as tracked by the node
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The CorDapp provider
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--------------------
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The CorDapp provider is where new CorDapps are installed to extend the behavior of the node.
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The node also has several CorDapps installed by default to handle common tasks such as:
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* Retrieving transactions and attachments from counterparties
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* Upgrading contracts
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* Broadcasting agreed ledger updates for recording by counterparties
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Draining mode
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^^^^^^^^^^^^^
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In order to operate a clean shutdown of a node, it is important than no flows are in-flight, meaning no checkpoints should
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be persisted. The node is able to be put in a Flows Draining Mode, during which:
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* Commands requiring to start new flows through RPC will be rejected.
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* Scheduled flows due will be ignored.
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* Initial P2P session messages will not be processed, meaning peers will not be able to initiate new flows involving the node.
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* All other activities will proceed as usual, ensuring that the number of in-flight flows will strictly diminish.
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As their number - which can be monitored through RPC - reaches zero, it is safe to shut the node down.
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This property is durable, meaning that restarting the node will not reset it to its default value and that a RPC command is required. |