e9e24f47ec
This PR implements a procedure that upgrades existing clusters to use raft-based topology operations. The procedure does not start automatically, it must be triggered manually by the administrator after making sure that no topology operations are currently running. Upgrade is triggered by sending `POST /storage_service/raft_topology/upgrade` request. This causes the topology coordinator to start who drives the rest of the process: it builds the `system.topology` state based on information observed in gossip and tells all nodes to switch to raft mode. Then, topology coordinator runs normally. Upgrade progress is tracked in a new static column `upgrade_state` in `system.topology`. The procedure also serves as an extension to the current recovery procedure on raft. The current recovery procedure requires restarting nodes in a special mode which disables raft, perform `nodetool removenode` on the dead nodes, clean up some state on the nodes and restart them so that they automatically rebuild the group 0. Raft topology fits into existing procedure by falling back to legacy topology operations after disabling raft. After rebuilding the group 0, upgrade needs to be triggered again. Because upgrade is manual and it might not be convenient for administrators to run it right after upgrading the cluster, we allow the cluster to operate in legacy topology operations mode until upgrade, which includes allowing new nodes to join. In order to allow it, nodes now ask the cluster about the mode they should use to join before proceeding by using a new `JOIN_NODE_QUERY` RPC. The procedure is explained in more detail in `topology-over-raft.md`. Fixes: https://github.com/scylladb/scylladb/issues/15008 Closes scylladb/scylladb#17077 * github.com:scylladb/scylladb: test/topology_custom: upgrade/recovery tests for topology on raft cdc/generation_service: in legacy mode, fall back to raft tables system_keyspace: add read_cdc_generation_opt cdc/generation_service: turn off gossip notifications in raft topo mode cql_test_env: move raft_topology_change_enabled var earlier group0_state_machine: pull snapshot after raft topology feature enabled storage_service: disable persistent feature enabler on upgrade storage_service: replicate raft features to system.peers storage_service: gossip tokens and cdc generation in raft topology mode API: add api for triggering and monitoring topology-on-raft upgrade storage_service: infer which topology operations to use on startup storage_service: set the topology kind value based on group 0 state raft_group0: expose link to the upgrade doc in the header feature_service: fall back to checking legacy features on startup storage_service: add fiber for tracking the topology upgrade progress gms: feature_service: add SUPPORTS_CONSISTENT_TOPOLOGY_CHANGES topology_coordinator: implement core upgrade logic topology_coordinator: extract top-level error handling logic storage_service: initialize discovery leader's state earlier topology_coordinator: allow for custom sharding info in prepare_and_broadcast_cdc_generation_data topology_coordinator: allow for custom sharding info in prepare_new_cdc_generation_data topology_coordinator: remove outdated fixme in prepare_new_cdc_generation_data topology_state_machine: introduce upgrade_state storage_service: disallow topology ops when upgrade is in progress raft_group0_client: add in_recovery method storage_service: introduce join_node_query verb raft_group0: make discover_group0 public raft_group0: filter current node's IP in discover_group0 raft_group0: remove my_id arg from discover_group0 storage_service: make _raft_topology_change_enabled more advanced docs: document raft topology upgrade and recovery
Scylla developer documentation
This folder contains developer-oriented documentation concerning the ScyllaDB codebase. We also have a wiki, which contains additional developer-oriented documentation. There is currently no clear definition of what goes where, so when looking for something be sure to check both.
Seastar documentation can be found here.
User documentation can be found on docs.scylladb.com
For information on how to build Scylla and how to contribute visit HACKING.md and CONTRIBUTING.md.