Tag: Docker

Setup MySQL on Docker – Order Matters

I wanted to create a new container on my Docker host for MySQL today. In general not a big deal. Pull the image from the repository and execute a docker run command along with some parameters and options to create the container.
I followed the instructions on https://hub.docker.com/_/mysql but ran into an issue, where the container started but exited after a couple of seconds.

I had created two volumes that should be mapped to the container to keep the configuration and the data persitent.

docker volume create mysql-data
docker volume create mysql-conf

Tis is not necessary because docker creates a volume when it creates the container. But the volume name is a cryptic string, and I wanted to have it in a human readable form.
I used the following command to create the container. I ran it without the -d option to be able to see output in the shell.

docker run --name=mysqlsrv -e MYSQL_ROOT_PASSWORD=SecretPassw0rd mysql:latest -p 3306:3306 -p 33060:33060 -v mysql-data:/var/lib/mysql -v mysql-conf:/etc/mysql

The container started, but then stopped.

2020-11-21 09:11:50+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 8.0.22-1debian10 started.
2020-11-21 09:11:50+00:00 [Note] [Entrypoint]: Switching to dedicated user 'mysql'
2020-11-21 09:11:50+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 8.0.22-1debian10 started.
2020-11-21 09:11:50+00:00 [Note] [Entrypoint]: Initializing database files
2020-11-21T09:11:50.346284Z 0 [ERROR] [MY-010083] [Server] --verbose is for use with --help; did you mean --log-error-verbosity?
2020-11-21T09:11:50.346355Z 0 [System] [MY-013169] [Server] /usr/sbin/mysqld (mysqld 8.0.22) initializing of server in progress as process 42
2020-11-21T09:11:50.351718Z 1 [System] [MY-013576] [InnoDB] InnoDB initialization has started.
2020-11-21T09:11:55.615069Z 1 [System] [MY-013577] [InnoDB] InnoDB initialization has ended.
2020-11-21T09:12:02.486299Z 0 [ERROR] [MY-010147] [Server] Too many arguments (first extra is 'my-sql-data:/var/lib/mysql').
2020-11-21T09:12:02.486810Z 0 [ERROR] [MY-013236] [Server] The designated data directory /var/lib/mysql/ is unusable. You can remove all files that the server added to it.
2020-11-21T09:12:02.487256Z 0 [ERROR] [MY-010119] [Server] Aborting
2020-11-21T09:12:07.897884Z 0 [System] [MY-010910] [Server] /usr/sbin/mysqld: Shutdown complete (mysqld 8.0.22) MySQL Community Server - GPL.

After some try and error it turned out that the order of the parameters matter. You have to put the -p and -v parameters before the mysql:tag. 

docker run -d -p 3306:3306 -p 33060:33060 -v mysql-data:/var/lib/mysql -v mysql-conf:/etc/mysql --name=mysqlsrv -e MYSQL_ROOT_PASSWORD=SecretPassw0rd mysql:latest

After that MySQL starts and maps the volumes in /var/lib/docker/volumes to the paths inside the container.


Docker – Prevent Container Autostart

Docker will autostart any container with a RestartPolicy of ‘always’ when the docker service initially starts.

I’ve mostly had this situation occur when a container was created with –restart always, and the situation later changed such that I no longer wanted this to happen.

You won’t find any evidence of this within cron or any other normal system startup scripts; you’ll have to dig into the container configuration to find it.

In order to quickly find the RestartPolicy config, you can use 

docker inspect my-container | grep -A 3 RestartPolicy

The -A n grep option shows n lines after the match.

To update the RestartPolicy config you can use

docker update --restart=no my-container

Here is a sample from one of my containers.

docker inspect c2ea02bc1349 | grep -A 3 RestartPolicy
"RestartPolicy": {
"Name": "always",
"MaximumRetryCount": 0
},

docker update --restart=no c2ea02bc1349

docker inspect c2ea02bc1349 | grep -A 3 RestartPolicy
"RestartPolicy": {
"Name": "no",
"MaximumRetryCount": 0
},