Make the removenode operation go through the `left_token_ring` state, similar to decommission. This ensures that when removenode completes, all nodes in the cluster are aware of the topology change through a global token metadata barrier.
Previously, removenode would skip the `left_token_ring` state and go directly from `write_both_read_new` to `left` state. This meant that when the operation completed, some nodes might not yet know about the topology change, potentially causing issues with subsequent data plane requests.
Key changes:
- Both decommission and removenode now transition to `left_token_ring` state in the `write_both_read_new` handler
- In `left_token_ring` state, only decommissioning nodes receive the shutdown RPC (removed nodes are already dead)
- Updated documentation to reflect that both operations use this state
This change improves consistency guarantees for removenode operations by ensuring cluster-wide awareness before completion.
The change is protected by "REMOVENODE_WITH_LEFT_TOKEN_RING" feature flag to also support mixed clusters during e.g. upgrade.
Fixes: scylladb/scylladb#25530
No backport: This fixes and issue found in tests. It can theoretically happen in production too, but wasn't reported in any customer issue, so a backport is not needed.
Closesscylladb/scylladb#26931
* https://github.com/scylladb/scylladb:
topology: make removenode use left_token_ring state for global barrier
topology: allow removing nodes not having tokens
features: add feature flag for removenode via left token ring
d5c205194b