gid, uid, mount volume

[Brandstetter]

RHEL 7.4 (SELinux enabled)
docker version 1.12.6
docker compose 1.15
docker compose file version 2
mysql 5.7

mysql/5.7/Dockerfile:
line 4: RUN groupadd -r mysql && useradd -r -g mysql mysql
=> user mysql uid=999 and group mysql gid=999

docker-compose file:
mysql:
image: mysql:5.7
...
volumes:
- "${DATA_DIR}/mysql_data:/var/lib/mysql:Z"
- "${BACKUP_DIR}/mysql_backup:/mysql_backup:Z"

BUT this uid and gid are already used on the host system.
DATA_DIR looks like that:
drwxr-xr-x 8 polkitd ssh_keys 4.0K 2018-03-20 13:38:30 mysql_data
And user polkitd and group ssh_keys can have different access rights as the indended mysql...

How can I start the mysql container and have uid and gid as input parameter? (of course I have to create the mysql user and group on the host system first).

[yosifkit]

Just use --user on docker run (or the compose equivalent) to run as whatever user you want. They'll need to already own the folders you are mounting in since it has to skip chowning since it is not root:

$ docker run -d --user 1000:1000 -e .... mysql

[alexanderadam]

So what should be the workflow if someone wants to work with another UID/GID?

1. regular initialization (without setting the IDs)
2. chowning
3. then running by setting the IDs?