Configuration

We can bootstrap a NATS Streaming cluster by providing the cluster topology using the -cluster_peers flag. This is simply the set of node IDs participating in the cluster. Note that once a leader is established, we can start subsequent servers without providing this configuration as they will automatically join the leader. If the server is recovering, it will use the recovered cluster configuration.

Here is an example of starting three servers in a cluster. For this example, we run a separate NATS server which the Streaming servers connect to.

  1. nats-streaming-server -store file -dir store-a -clustered -cluster_node_id a -cluster_peers b,c -nats_server nats://localhost:4222
  3. nats-streaming-server -store file -dir store-b -clustered -cluster_node_id b -cluster_peers a,c -nats_server nats://localhost:4222
  5. nats-streaming-server -store file -dir store-c -clustered -cluster_node_id c -cluster_peers a,b -nats_server nats://localhost:4222

Note that once a leader is elected, subsequent servers can be started without providing the cluster configuration. They will automatically join the cluster. Similarly, the cluster node ID does not need to be provided as one will be automatically assigned. As long as the file store is used, this ID will be recovered on restart.

  1. nats-streaming-server -store file -dir store-d -clustered -nats_server nats://localhost:4222

The equivalent clustering configurations can be specified in a configuration file under the cluster group. See the Configuring section for more information.

Here is an example of a cluster of 3 nodes using the following configuration files. The nodes are running on host1, host2 and host3 respectively. NOTE If you have an existing NATS cluster and want to run NATS Streaming Cluster on top of that, see details at the end of this section.

On host1, this configuration indicates that the server will accept client connections on port 4222. It will accept route connections on port 6222. It creates 2 routes, to host2 and host3 cluster port.

It defines the NATS Streaming cluster name as mycluster, uses a store file that points to the store directory. The cluster section inside streaming makes the NATS Streaming server run in cluster mode. This configuration explicitly define each node id (a for host1) and list its peers.

  1. # NATS specific configuration
  2. port: 4222
  3. cluster {
  4.   listen: 0.0.0.0:6222
  5.   routes: ["nats://host2:6222", "nats://host3:6222"]
  6. }
  8. # NATS Streaming specific configuration
  9. streaming {
  10.   id: mycluster
  11.   store: file
  12.   dir: store
  13.   cluster {
  14.     node_id: "a"
  15.     peers: ["b", "c"]
  16.   }
  17. }

Below is the configuration for the server running on host2. Notice how the routes are now to host1 and host3. The other thing that changed is the node id that is set to b and peers are updated accordingly to a and c.

Note that the dir configuration is also store but these are local directories and do not (actually must not) be shared. Each node will have its own copy of the datastore. You could have each configuration have a different value for dir if desired.

  1. # NATS specific configuration
  2. port: 4222
  3. cluster {
  4.   listen: 0.0.0.0:6222
  5.   routes: ["nats://host1:6222", "nats://host3:6222"]
  6. }
  8. # NATS Streaming specific configuration
  9. streaming {
  10.   id: mycluster
  11.   store: file
  12.   dir: store
  13.   cluster {
  14.     node_id: "b"
  15.     peers: ["a", "c"]
  16.   }
  17. }

As you would expect, for host3, the routes are now to host1 and host2 and the node id is c while its peers are a and b.

  1. # NATS specific configuration
  2. port: 4222
  3. cluster {
  4.   listen: 0.0.0.0:6222
  5.   routes: ["nats://host1:6222", "nats://host2:6222"]
  6. }
  8. # NATS Streaming specific configuration
  9. streaming {
  10.   id: mycluster
  11.   store: file
  12.   dir: store
  13.   cluster {
  14.     node_id: "c"
  15.     peers: ["a", "b"]
  16.   }
  17. }

In the example above, the configuration assumes no existing NATS Cluster and therefore configure the NATS routes between each node. Should you want to use an existing NATS cluster, do not include the “NATS specific configuration” section, instead, add nats_server_url in the streaming section to point to the NATS server you want.