I have a CI job that instantiate postgreql using 9.4-alpine image. Job suddenly failed because database won't start.
Up until the failure, the image id used is 48d6bb3f0449. The new postgresql image used in the failed job has an id of 65a424ba5ff8.

The error the database throws at startup is:

ERROR:  role "postgres" does not exist

Same problem happens when I use the 9.4.19-alpine image.
I've resolved this issue by using the 9.4.18-alpine image.

So there seems to be something wrong with the current 9.4.19-alpine image.