How to test a file exists from a Kubernetes probe?

I have a sidecar container in a MySQL Pod which will use the MySQL socket file in order to access the database.

I would like to be sure MySQL has successfully started and therefore have created the socket file before than this sidecar container starts.

I tried to add a readiness probe with an exec.command being test -S /var/run/mysqld/mysqld.sock but it fails with:

Readiness probe failed: OCI runtime exec failed: exec failed: container_linux.go:380: starting container process caused: exec: "test -S /var/run/mysqld/mysqld.sock": stat test -S /var/run/mysqld/mysqld.sock: no such file or directory: unknown

When I open a terminal session in the sidecar container, I can ls the socket file and it's there.

So it looks like my test -S <path> command doesn't work as expected in the context of the probe.

How can I write my probe so that as soon as the socket file is available my sidecar container starts?

Solution

Try:

...
readinessProbe:
  exec:
    command:
    - sh
    - -c
    - test -S /var/run/mysqld/mysqld.sock