Runner user creation fails in Docker image

[ikajdan]

When trying to create user in a Dockerfile, the adduser command fails to create the user properly.

Step 8/12 : RUN adduser --uid 1001 --group --no-create-home --home /app lava-gitlab-runner
 ---> Running in ed6183c2b7eb
adduser: Warning: The home dir /app you specified can't be accessed: No such file or directory
Adding group `lava-gitlab-runner' (GID 1000) ...
Done.

Only the group is created, but the user is not:

root@e3e08149d8e0:/# tail /etc/passwd
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
irc:x:39:39:ircd:/run/ircd:/usr/sbin/nologin
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
_apt:x:100:65534::/nonexistent:/usr/sbin/nologin

root@e3e08149d8e0:/# tail /etc/group 
shadow:x:42:
utmp:x:43:
video:x:44:
sasl:x:45:
plugdev:x:46:
staff:x:50:
games:x:60:
users:x:100:
nogroup:x:65534:
lava-gitlab-runner:x:1000:

This leads to the following error when trying to run a container:

$ docker run -it --rm ghcr.io/collabora/lava-gitlab-runner:v0.3.2
docker: Error response from daemon: unable to find user lava-gitlab-runner: no matching entries in passwd file.