Leaf Nodes
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A Leaf Node extends an existing NATS system of any size, optionally bridging both operator and security domains. A leafnode server will transparently route messages as needed from local clients to one or more remote NATS system(s) and vice versa. The leaf node authenticates and authorizes clients using a local policy. Messages are allowed to flow to the cluster or into the leaf node based on leaf node connection permissions of either.
Leaf nodes are useful in IoT and edge scenarios and when the local server traffic should be low RTT and local unless routed to the super cluster. NATS' queue semantics are honored across leaf connections by serving local queue consumer first.
Clients to leaf nodes authenticate locally (or just connect if authentication is not required)
Traffic between the leaf node and the cluster assumes the restrictions of the user configuration used to create the leaf connection.
Subjects that the user is allowed to publish are exported to the cluster.
Subjects the user is allowed to subscribe to, are imported into the leaf node.
Unlike or nodes, leaf nodes do not need to be reachable themselves and can be used to explicitly configure any acyclic graph topologies.
If a leaf node connects to a cluster, it is recommended to configure it with knowledge of all seed servers and have each seed server accept connections from leaf nodes. Should the remote cluster's configuration change, the discovery protocol will gossip peers capable of accepting leaf connections. A leaf node can have multiple remotes, each connecting to a different cluster. Each URL in a remote needs to point to the same cluster. If one node in a cluster is configured as leaf node, all nodes need to. Likewise, if one server in a cluster accepts leaf node connections, all servers need to.
Leaf Nodes are an important component as a way to bridge traffic between local NATS servers you control and servers that are managed by a third-party. Synadia's allows accounts to use leaf nodes, but gain accessibility to the global network to inexpensively connect geographically distributed servers or small clusters.
The main server is just a standard NATS server. Clients to the main cluster are just using token authentication, but any kind of authentication can be used. The server allows leaf node connections at port 7422 (default port):
Start the server:
We create a replier on the server to listen for requests on 'q', which it will aptly respond with '42':
The leaf node, allows local clients to connect to through port 4111, and doesn't require any kind of authentication. The configuration specifies where the remote cluster is located, and specifies how to connect to it (just a simple token in this case):
Note the leaf node configuration lists a number of remotes. The url specifies the port on the server where leaf node connections are allowed.
Start the leaf node server:
Connect a client to the leaf server and make a request to 'q':
Once you have the ngs tool installed, you can go ahead and import the synadia operator from ngs:
In order to use leaf nodes, you'll have to upgrade the account to the developer plan. The developer plan has zero cost, but requires specifying an email and providing a credit card number:
Check your email, verify the email, and specify an credit card, after that:
Note the limits on the account, specify that the account can have up-to 2 leaf node connections. Let's use them:
Let's craft a leaf node connection much like we did earlier:
The default port for leaf nodes is 7422, so we don't have to specify it.
Let's start the leaf server:
Again, let's connect a replier, but this time to NGS. NSC connects specifying the credentials file:
And now let's make the request from the local host:
In this example, we connect a leaf node to . Leaf nodes are supported on developer and paid accounts. To sign up for a developer account, you'll need the ngs tool which you can install by following instructions in .
In some cases you may want to restrict what messages can be exported from the leaf node or imported from the leaf connection. You can specify restrictions by limiting what the leaf connection client can publish and subscribe to. See for how you can do this.