We can also bootstrap a NATS Streaming cluster by starting one server as the seed node using the -cluster_bootstrap flag. This node will elect itself leader, so it's important to avoid starting multiple servers as seed. Once a seed node is started, other servers will automatically join the cluster. If the server is recovering, it will use the recovered cluster configuration.
Here is an example of starting three servers in a cluster by starting one as the seed and letting the others automatically join:
nats-streaming-server -store file -dir store-a -clustered -cluster_bootstrap -nats_server nats://localhost:4222
nats-streaming-server -store file -dir store-b -clustered -nats_server nats://localhost:4222
nats-streaming-server -store file -dir store-c -clustered -nats_server nats://localhost:4222
For a given cluster ID, if more than one server is started with cluster_bootstrap set to true, each server with this parameter will report the misconfiguration and exit.
The very first server that bootstrapped the cluster can be restarted, however, the operator must remove the datastores of the other servers that were incorrectly started with the bootstrap parameter before attempting to restart them. If they are restarted with existing state, even without the -cluster_bootstrap parameter, they will once again start as a leader.