As discussed in slack https://apachesolr.slack.com/archives/C022UMAPZ0V/p1676970790552379

When the operator restarts the cluster, e.g. during a version upgrade, there is no guarantee that a Solr POD is marked as not ready before solr stop is called. Thus clients may experience connection error during the restart.

@HoustonPutman suggests we can implement a custom readiness gate https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle/#pod-readiness-gate to control this better.