Apache Ignite : NODE_LEFT event

Question

I wanted to understand the how a Node left event is triggered for an Apache Ignite grid.

• Do nodes keep pinging each other constantly to find it if nodes are present or they ping each other only when required?
• If ping from client node is not successful then can it also trigger NODE_LEFT event or it can only be triggered by server node.
• Once a node has left, then which node triggers topology update event i.e. PME. Can it be triggered by client node or only server nodes can trigger it.

Answer 1

Yes, nodes are pinging each other to verify the connection. Here is more detailed explanation of how a node failure happens. You might also check this video.

The final decision of failing a node (leaving the cluster) is made on the Coordinator node issuing a special event that has to be acked by other nodes (NODE FAILED).

Though a node might leave a cluster explicitly, sending a TcpDiscoveryNodeLeftMessage (aka triggering a NODE_LEFT event), for example when you stop it gracefully.

Only the coordinator node can change topology version, meaning that a PME always starts on the coordinator and is spread to other nodes afterward.