Add registerControllerWithoutLeaderElection for per-replica controllers#4193
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Controllers that only maintain per-process, in-memory state which a replica's own API server depends on (and never write to storage) must run on every replica, not just the elected leader. Previously the only such case — the DynamicRESTMapper builtin/dynamic controllers — was wired through a bespoke post-start hook guarded by a sync.Once. Generalize that into the controller framework: add a controllersWithoutLeaderElection registry with registerControllerWithoutLeaderElection(), started once per process from the kcp-start-controllers post-start hook via startControllersWithoutLeaderElection(), independent of the leader-election machinery. This mirrors registerController()/ startControllers() for the leader-elected set. Convert the DynamicRESTMapper controllers to register through it, removing the one-off hook and the sync.Once/cached-error fields. installDynamicRESTMapper is idempotent (installControllers can run again on leadership re-acquisition): it returns early if the controllers are already registered, so their informer event handlers are not added twice. No functional change: the DynamicRESTMapper controllers still run on every replica exactly once.
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Summary
Controllers that only maintain per-process, in-memory state which a replica's own API server depends on (and never write to storage) must run on every replica, not just the elected leader. Previously the only such case — the DynamicRESTMapper builtin/dynamic controllers — was wired through a bespoke post-start hook guarded by a sync.Once.
Generalize that into the controller framework: add a controllersWithoutLeaderElection registry with registerControllerWithoutLeaderElection(), started once per process from the kcp-start-controllers post-start hook via startControllersWithoutLeaderElection(), independent of the leader-election machinery. This mirrors registerController()/ startControllers() for the leader-elected set.
Convert the DynamicRESTMapper controllers to register through it, removing the one-off hook and the sync.Once/cached-error fields. installDynamicRESTMapper is idempotent (installControllers can run again on leadership re-acquisition): it returns early if the controllers are already registered, so their informer event handlers are not added twice.
No functional change: the DynamicRESTMapper controllers still run on every replica exactly once.
What Type of PR Is This?
/kind chore
Related Issue(s)
Fixes #
Release Notes