Comment 3 for bug 1975500

The cause is here:

unit-kubernetes-control-plane-1: 09:05:11 WARNING unit.kubernetes-control-plane/1.vault-kv-relation-changed hvac.exceptions.InternalServerError: 1 error occurred:
unit-kubernetes-control-plane-1: 09:05:11 WARNING unit.kubernetes-control-plane/1.vault-kv-relation-changed * failed to write: dial tcp 127.0.0.1:3306: connect: connection refused
unit-kubernetes-control-plane-1: 09:05:11 WARNING unit.kubernetes-control-plane/1.vault-kv-relation-changed
unit-kubernetes-control-plane-1: 09:05:11 WARNING unit.kubernetes-control-plane/1.vault-kv-relation-changed , on post http://172.31.36.61:8200/v1/charm-e34c99d9-06c4-445c-8f56-3d5547baaff2-kubernetes-control-plane/kv/app-hashes/1
unit-kubernetes-control-plane-1: 09:05:11 DEBUG juju.worker.uniter.remotestate got leader settings change for kubernetes-control-plane/1: ok=true

i.e. the local mysql router (…:3306) is not available.

Whilst there is an issue with robustness in the vault charm (e.g. it error's out), this (almost certainly) would recover if the hook was retried when the local mysql-router instance is available.

It would be very useful if you could dig into this and work out what was happening with the mysql-router at the time of the hook error in vault.