MySQL Docker Container storing password after first run

Question

All my experience with Docker so far has led me to believe that containers are stateless.

If so, why is my container storing the password that I change it to after the first run if I spun it up without specifying a volume or bind mount? I am especially puzzled since none of the other edits I make to the dbms persist (like creating tables).

Additional Details:
Versions:
1. Docker - 18.09.0 build 4d60db4
2. Image - mysql/mysql-server:latest

Commands:
1. $ docker run --name=sql -d mysql/mysql-server:latest
2. $ docker logs sql 2>&1 | grep GENERATED $ docker logs sql 2>&1 | grep GENERATED to grab the generated password for first login
3. $ docker exec -it sql mysql -uroot -p
4. mysql> Enter Password: <generated password>
5. mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'stkoverflw';
6. mysql> exit
7. $ docker stop sql
8. $ docker start sql
9. $ docker exec -it sql mysql -uroot -p
10. mysql> Enter Password: <stkoverflw>

How does the password configuration persist across restarts of the container?

Answer 1

Containers are not stateless. Containers are easy to create and destroy, so they can be used to run a service which is stateless, but each container is itself stateful.

When the container is running, there is a volume containing its root filesystem. You don't have to tell Docker to create it. Docker has to create it because otherwise where do the container's files go?

When you say docker stop , the container stops running but it is not destroyed. When you say docker start , the same container resumes with the same root volume. That's where the changed password persists. The process running in the container was stopped and a new process was started (so state held in memory would be lost), but the filesystem is still there.

To get rid of a container (including the changed password), say docker rm . Then you can say docker run to start from scratch.