Service Member Statuses

Master service members have four possible statuses that affect their ability to handle messages. The following figure shows the four possible states and the associated transitions.

[status image here]

States

• Down: The service member is not reachable by other service members. It may not handle messages. A node is forced to Down whenever an external problem affects its ability to handle messages, or after a shutdown.
• Joining: A status used as a transition step between down and up. While in joining status, the service member makes sure it is ready to go Up before switching.
• Up: The service member is up and running. It can handle traffic.
• Leaving: A status used to shutdown the node. The service member sits in leaving status until every other class impacted by the shutdown allows the switch.

Transition Context

The following transition are performed naturally with a periodic status promotion attempt mechanism:

• Down -> Joining
• Joining -> Up
• Leaving -> Down

The following transition are "forced" when an external event occurs:

• Up -> Leaving (on application shutdown)
• Up -> Down (when a problem occurs like a consistency error)