No switchover candidate found

[dobrac]

Please, answer some short questions which should help us to understand your problem / question better?

• Which image of the operator are you using? registry.opensource.zalan.do/acid/postgres-operator:v1.8.2
• Where do you run it - cloud or metal? Kubernetes or OpenShift? Bare Metal K8s (microk8s)
• Are you running Postgres Operator in production? yes
• Type of issue? Bug report

Helllo,

we are encountering an error while cluster updating (any change in the configuration that needs pods restart), where the master is not correctly switched to the synchronous replica. We have 2 instances, one is master and one is a synchronous replica.

Here is log from the operator, the problem occurs every time:

time="2022-08-10T11:39:52Z" level=info msg="reason: new statefulset containers's postgres (index 0) environment does not match the current one" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:39:52Z" level=debug msg="updating statefulset" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:39:53Z" level=debug msg="making GET http request: http://10.1.63.119:8008/config" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:05Z" level=debug msg="making GET http request: http://10.1.11.85:8008/patroni" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:05Z" level=debug msg="making GET http request: http://10.1.63.119:8008/patroni" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:05Z" level=debug msg="performing rolling update" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:05Z" level=info msg="there are 2 pods in the cluster to recreate" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:05Z" level=debug msg="subscribing to pod "postgres-qplay/qplay-prod-0"" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:27Z" level=info msg="pod "postgres-qplay/qplay-prod-0" has been recreated" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:27Z" level=debug msg="unsubscribing from pod "postgres-qplay/qplay-prod-0" events" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:27Z" level=debug msg="making GET http request: http://10.1.63.119:8008/cluster" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:27Z" level=warning msg="error while syncing cluster state: could not sync statefulsets: could not recreate pods: skipping switchover: no switchover candidate found" cluster-name=postgres-qplay/qplay-prod pkg=cluster time="2022-08-10T11:40:27Z" level=error msg="could not sync cluster: could not sync statefulsets: could not recreate pods: skipping switchover: no switchover candidate found" cluster-name=postgres-qplay/qplay-prod pkg=controller worker=0 time="2022-08-10T11:40:27Z" level=info msg="received add event for already existing Postgres cluster" cluster-name=postgres-qplay/qplay-prod pkg=controller worker=0

Any idea what could be wrong? It could be definitely some wrong configuration (maybe three instances are the minimum?), but I can't figure out that it is.

[FxKu]

Are both instances healthy? "no switchover candidate found" sounds like no healthy replica has been found.

[dobrac]

I’m not fully sure if the second one is successfully restarted (and healthy) at that moment, but it’s definitely healthy after short time. If I do manual switchover using patronictl, everything is working well.

I haven’t manage to do successful switchover while updating, it fails every time.

[bootc]

I am also running into this issue, but I'm not sure it's exactly like OP. Like @dobrac I can exec into the pod and force a switchover and all is well, but the Operator fails to do the switchover when pods need evicting:

time="2024-01-14T09:34:53Z" level=info msg="starting process to migrate master pod \"gitlab/gitlab-postgres-1\"" cluster-name=gitlab/gitlab-postgres pkg=cluster
time="2024-01-14T09:34:54Z" level=debug msg="making GET http request: http://10.44.95.149:8008/cluster" cluster-name=gitlab/gitlab-postgres pkg=cluster
time="2024-01-14T09:34:54Z" level=error msg="could not move master pod \"gitlab/gitlab-postgres-1\": could not find suitable replica pod as candidate for failover: no switchover candidate found" pkg=controller

The cluster status from the URI mentioned is:

{
  "members": [
    {
      "name": "gitlab-postgres-0",
      "role": "replica",
      "state": "streaming",
      "api_url": "http://10.44.22.248:8008/patroni",
      "host": "10.44.22.248",
      "port": 5432,
      "timeline": 63,
      "lag": 0
    },
    {
      "name": "gitlab-postgres-1",
      "role": "leader",
      "state": "running",
      "api_url": "http://10.44.95.149:8008/patroni",
      "host": "10.44.95.149",
      "port": 5432,
      "timeline": 63
    },
    {
      "name": "gitlab-postgres-2",
      "role": "replica",
      "state": "streaming",
      "api_url": "http://10.44.98.184:8008/patroni",
      "host": "10.44.98.184",
      "port": 5432,
      "timeline": 63,
      "lag": 0
    }
  ]
}

This is with Postgres Operator 1.10.1 and spilo-15:3.1-p1 on Kubernetes 1.28.5 using Rancher RKE2 on on-prem VMs and bare metal.

It looks like the "state": "streaming" is not accounted for; the code expects "state": "running" to find candidates.

[macedigital]

Thank you @bootc for picking this up and providing a solution :+1:

It seems it might trace down to a change introduced here https://github.com/zalando/patroni/commit/d46ca88e6bb4b4788ec86689026c2d2e4da68c79.

We'll aim to merge the fix next week.

[macedigital]

Thank you @bootc for your contribution!