Promoting the standby cluster requires updating load-balancer health checks, which is not very convenient and easy to forget.
In order to solve it, we change the behavior of the `/leader` health-check endpoint. It will return 200 without taking into account whether PostgreSQL is running as the primary or the standby_leader.
So far Patroni was enforcing the same value of `wal_keep_segments` on all nodes in the cluster. If the parameter was missing from the global configuration it was using the default value `8`.
In pg13 beta3 the `wal_keep_segments` was renamed to the `wal_keep_size` and it broke Patroni.
If `wal_keep_segments` happened to be present in the configuration for pg13, Paroni will recalculate the value to `wal_keep_size` assuming that the `wal_segment_size` is 16MB. Sure, it is possible to get the real value of `wal_segment_size` from pg_control, but since we are dealing with the case of misconfiguration it is not worse time spend on it.
- ``GET /replica?lag=<max-lag>``: replica check endpoint.
- ``GET /asynchronous?lag=<max-lag>`` or ``GET /async&lag=<max-lag>``: asynchronous standby check endpoint.
Checks replication latency and returns status code **200** only when the latency is below a specified value. The key leader_optime from DCS is used for the leader WAL position and compute latency on the replica for performance reasons. Please note that the value in leader_optime might be a couple of seconds old (based on loop_wait).
Co-authored-by: Alexander Kukushkin <cyberdemn@gmail.com>
They could be useful to eliminate "unhealthy" pods from subsets addresses when the K8s service with label selectors are used.
Real-life example: the node where the primary was running has failed and being shutdown and Patroni can't update (remove) the role label.
Therefore on OpenShift the leader service will have two pods assigned, one of them is a failed primary.
With the readiness probe defined, the failed primary pod will be excluded from the list.
