Docker Compose Detach Mode Parameter Error - docker

Question

Here is my docker-compose file, mysql.yml:
# Use root/example as user/password credentials
version: '3'
services:
db:
image: mysql
tty: true
stdin_open: true
command: --default-authentication-plugin=mysql_native_password
container_name: db
restart: always
networks:
- db
ports:
- 3306:3306
environment:
MYSQL_ROOT_PASSWORD: example1
command: bash -c "apt update"
adminer:
image: adminer
restart: always
container_name: web
networks:
- db
ports:
- 8080:8080
volumes:
- ./data/db:/var/lib/mysql
networks:
db:
external: true
When I run this file as "docker-compose -f mysql.yml up -d" it starts working, but after 5 or 10 seconds it dies with 0 exit code. Then, it restarts due to "restart: always" parameter.
I search on the internet about my problem and got some solutions:
First one,
tty: true
std_in_open: true
parameters, but they are not working. The container dies anyway.
Second one,
entrypoint:
- bash
- -c
command:
- |
tail -f /dev/null
This solution is working, but it overrides the default entrypoint, and, so my MySQL service does not work at the end.
Yes, I can concatenate entrypoints or create a Dockerfile(I actually want to complete all this in a single file), but I think it' s not the right way and I need some advice.
Thanks in advance!

Answer 1

When your Compose setup says:
command: bash -c "apt update"
This is the only thing the container does; this runs instead of the normal container process. Once that command completes (successfully) the container will exit (with status code 0).
In normal operation you shouldn't need to specify the command: for a container; the Dockerfile will have a CMD line that provides a useful default. (The notable exception is a setup where you have both a Web server and a background worker sharing substantial code, so you can set CMD to run, say, the Flask application but override command: to run a Celery worker.)
Many of the other options you include in the docker-compose.yml file are unnecessary. You can safely remove tty:, stdin_open:, container_name:, and networks: with no ill effects. (You can configure the Compose-provided default network if you specifically need containers running on a pre-created network.)
The comments hint at trying to run package updates at container startup time. I'd echo #xdhmoore's comment here: you should only run APT or similar package managers during an image build, never on a running container. (You don't want your application startup to fail because a Debian mirror is down, or because an incompatible update has gotten deployed.)
For the standard Docker Hub images, in general they update somewhat frequently, especially if you're not pinning to a specific patch release. If you run
docker-compose pull
docker-compose up
it will ask Docker Hub for a newer version of the image, and recreate the container on it if needed.
The standard Docker Hub packages also frequently download and install the thing they're packaging outside their distribution's package manager system, so running an upgrade isn't necessarily useful.
If you must, though, the best way to do this is to write a minimal Dockerfile
FROM mysql
RUN apt-get update \
&& DEBIAN_FRONTEND=noninteractive \
apt-get upgrade --assume-yes
and reference it in the docker-compose.yml file
services:
db:
build: .
# replacing the image: line
# do NOT leave `image: mysql` behind