mirror of
https://github.com/corda/corda.git
synced 2024-12-28 08:48:57 +00:00
6edf95506b
Add changelog entry Address review comments Alternate solution to service queues Fixup after merge
104 lines
6.4 KiB
ReStructuredText
104 lines
6.4 KiB
ReStructuredText
Networking and messaging
|
|
========================
|
|
|
|
Corda uses AMQP/1.0 over TLS between nodes which is currently implemented using Apache Artemis, an embeddable message
|
|
queue broker. Building on established MQ protocols gives us features like persistence to disk, automatic delivery
|
|
retries with backoff and dead-letter routing, security, large message streaming and so on.
|
|
|
|
Artemis is hidden behind a thin interface that also has an in-memory only implementation suitable for use in
|
|
unit tests and visualisation tools.
|
|
|
|
.. note:: A future version of Corda will allow the MQ broker to be split out of the main node and run as a
|
|
separate server. We may also support non-Artemis implementations via JMS, allowing the broker to be swapped
|
|
out for alternative implementations.
|
|
|
|
There are multiple ways of interacting with the network. When writing an application you typically won't use the
|
|
messaging subsystem directly. Instead you will build on top of the :doc:`flow framework <flow-state-machines>`,
|
|
which adds a layer on top of raw messaging to manage multi-step flows and let you think in terms of identities
|
|
rather than specific network endpoints.
|
|
|
|
.. _network-map-service:
|
|
|
|
Network Map Service
|
|
-------------------
|
|
|
|
Supporting the messaging layer is a network map service, which is responsible for tracking public nodes on the network.
|
|
|
|
Nodes have an internal component, the network map cache, which contains a copy of the network map (which is just a
|
|
document). When a node starts up its cache fetches a copy of the full network map, and requests to be notified of
|
|
changes. The node then registers itself with the network map service, and the service notifies subscribers that a new
|
|
node has joined the network. Nodes do not automatically deregister themselves, so (for example) nodes going offline
|
|
briefly for maintenance are retained in the network map, and messages for them will be queued, minimising disruption.
|
|
|
|
Nodes submit signed changes to the map service, which then forwards update notifications on to nodes which have
|
|
requested to be notified of changes.
|
|
|
|
The network map currently supports:
|
|
|
|
* Looking up nodes by service
|
|
* Looking up node for a party
|
|
* Suggesting a node providing a specific service, based on suitability for a contract and parties, for example suggesting
|
|
an appropriate interest rates oracle for an interest rate swap contract. Currently no recommendation logic is in place.
|
|
|
|
Message queues
|
|
--------------
|
|
|
|
The node makes use of various queues for its operation. The more important ones are described below. Others are used
|
|
for maintenance and other minor purposes.
|
|
|
|
:``p2p.inbound.$identity``:
|
|
The node listens for messages sent from other peer nodes on this queue. Only clients who are authenticated to be
|
|
nodes on the same network are given permission to send. Messages which are routed internally are also sent to this
|
|
queue (e.g. two flows on the same node communicating with each other).
|
|
|
|
:``internal.peers.$identity``:
|
|
These are a set of private queues only available to the node which it uses to route messages destined to other peers.
|
|
The queue name ends in the base 58 encoding of the peer's identity key. There is at most one queue per peer. The broker
|
|
creates a bridge from this queue to the peer's ``p2p.inbound.$identity`` queue, using the network map service to lookup the
|
|
peer's network address.
|
|
|
|
:``internal.services.$identity``:
|
|
These are private queues the node may use to route messages to services. The queue name ends in the base 58 encoding
|
|
of the service's owning identity key. There is at most one queue per service identity (but note that any one service
|
|
may have several identities). The broker creates bridges to all nodes in the network advertising the service in
|
|
question. When a session is initiated with a service counterparty the handshake is pushed onto this queue, and a
|
|
corresponding bridge is used to forward the message to an advertising peer's p2p queue. Once a peer is picked the
|
|
session continues on as normal.
|
|
|
|
:``rpc.requests``:
|
|
RPC clients send their requests here, and it's only open for sending by clients authenticated as RPC users.
|
|
|
|
:``clients.$user.rpc.$random``:
|
|
RPC clients are given permission to create a temporary queue incorporating their username (``$user``) and sole
|
|
permission to receive messages from it. RPC requests are required to include a random number (``$random``) from
|
|
which the node is able to construct the queue the user is listening on and send the response to that. This mechanism
|
|
prevents other users from being able listen in on the responses.
|
|
|
|
Security
|
|
--------
|
|
|
|
Clients attempting to connect to the node's broker fall in one of four groups:
|
|
|
|
#. Anyone connecting with the username ``SystemUsers/Node`` is treated as the node hosting the broker, or a logical
|
|
component of the node. The TLS certificate they provide must match the one broker has for the node. If that's the case
|
|
they are given full access to all valid queues, otherwise they are rejected.
|
|
|
|
#. Anyone connecting with the username ``SystemUsers/Peer`` is treated as a peer on the same Corda network as the node. Their
|
|
TLS root CA must be the same as the node's root CA - the root CA is the doorman of the network and having the same root CA
|
|
implies we've been let in by the same doorman. If they are part of the same network then they are only given permission
|
|
to send to our ``p2p.inbound.$identity`` queue, otherwise they are rejected.
|
|
|
|
#. Every other username is treated as a RPC user and authenticated against the node's list of valid RPC users. If that
|
|
is successful then they are only given sufficient permission to perform RPC, otherwise they are rejected.
|
|
|
|
#. Clients connecting without a username and password are rejected.
|
|
|
|
Artemis provides a feature of annotating each received message with the validated user. This allows the node's messaging
|
|
service to provide authenticated messages to the rest of the system. For the first two client types described above the
|
|
validated user is the X.500 subject of the client TLS certificate. This allows the flow framework to authentically determine
|
|
the ``Party`` initiating a new flow. For RPC clients the validated user is the username itself and the RPC framework uses
|
|
this to determine what permissions the user has.
|
|
|
|
The broker also does host verification when connecting to another peer. It checks that the TLS certificate subject matches
|
|
with the advertised X.500 legal name from the network map service.
|