To statesync a node, you need at least 2x existing nodes with state-sync.snapshot-interval set to a non-zero value ({NAMESPACE}_SNAPSHOT_INTERVAL).
This example includes 2 deploy files - snapshot-deploy.yml for the two snapshotting nodes, and statesync-deploy for a third statesynced node.
We use the STATESYNC_RPC_SERVERS option which automatically configures statesync from the first node's RPC server, and configures both as the statesync.rpc-servers.
Alternatively you can configure statesync manually using the options in the docs