An internal PostgreSQL requires one variable to be available during installation or upgrade. If it is not set by the user, a random 10 character alphanumeric string will be set. Therefore, it is recommended to set this explicitly during installation and upgrade.
--set postgresql.postgresqlPassword=<value>
The values should remain same between upgrades. If this was auto-generated during helm install, the same password will have to be passed on future upgrades.
To read the current password, use the following command. For more information on reading a secret value, see Kubernetes: Decoding a Secret.
POSTGRES_PASSWORD=$(kubectl get secret -n <namespace><release_name>-postgresql -o jsonpath="{.data.postgresql-password}" | base64 --decode)The following parameter can be set during the upgrade:
--set postgresql.postgresqlPassword=${POSTGRES_PASSWORD}