Joining is the cluster-membership state assigned to a node after it requests admission but before the leader moves it to Up. It marks a transitional lifecycle stage rather than full cluster membership. section 8.2.3 section 8.6
A node typically passes through this sequence:
- A node discovers or contacts seed nodes and sends an InitJoin request. section 8.2.3 section 13.1.2
- The leader accepts the request and places the node in Joining. section 8.2.3
- When membership prerequisites are satisfied, the leader moves the node to Up. section 8.4.2 section 8.2.3
Joining a two-node cluster
A second seed node contacts the first node and receives an acknowledgement. The first node logs that the second is JOINING, then reports that the leader is moving it to Up. In a bootstrapped cluster, the first node can form the cluster and become Up before accepting the second node's join request. section 8.2.3 section 13.1.2
Cluster Node [akka://words@127.0.0.1:2551] - Sending InitJoinAck message
from node [akka://words@127.0.0.1:2551] to
[Actor[akka://words@127.0.0.1:2552/... #1
Cluster Node [akka://words@127.0.0.1:2551] - Node
[akka://words@127.0.0.1:2552] is JOINING, roles [seed, dc-default],
version [0.0.0] #2
Cluster Node [akka://words@127.0.0.1:2551] - Leader is moving node
[akka://words@127.0.0.1:2552] to [Up] #3
... #4
Inspect the runtime messages showing InitJoin acknowledgement, the Joining state, and the leader's transition to Up. section 8.2.3
