Today's kubelet-restart-induced switchovers on ak-pg and pprl-pg each
took ~5 minutes from probe-failure to authentik/paperless reconnecting,
dominated by ~4 minutes of postgres-internal promote work. Most of
that time is the new primary chasing missing WAL via barman-cloud (the
old primary terminated mid-stream, queued WAL had to be replayed from
the archive) and the standby waiting through wal_retrieve_retry_interval
cycles before noticing the promote trigger.
With one synchronous standby (`synchronous.number: 1`), the standby is
always at the same LSN as the primary at commit time, so on promote
there is no missing WAL to chase and the standby is immediately ready
to accept connections. CNPG switchovers in this mode complete in single
digits of seconds.
`dataDurability: preferred` (CNPG v1.20+ modern API, replaces the
legacy minSyncReplicas/maxSyncReplicas fields) makes sync best-effort:
the primary stops waiting for the standby if it becomes unavailable,
so a standby outage does not block writes. The trade-off versus async
is ~1-5 ms of added commit latency on healthy LAN+Ceph, which is well
under the noise floor for authentik and paperless workloads.
Single-instance clusters (im-pg, gf-pg) are not touched - sync
replication requires >= 2 instances.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
k.rennerandClaude Opus 4.7