在 docker-compose 中使用卷时删除 Mariadb 表

Question

I'm copy previous mariadb container's data(/var/lib/mysql) and paste data to new container image. this is Dockerfile

FROM mariadb:latest

ENV MYSQL_ROOT_PASSWORD tt
ENV MYSQL_DATABASE tt
ENV MYSQL_USER tt
ENV MYSQL_PASSWORD tt

# copy other database data
ADD mysql /var/lib/mysql
RUN chown -R mysql:mysql /var/lib/mysql

VOLUME /var/lib/mysql

EXPOSE 3306

CMD ["mysqld"]

when I build docker image, all table remained

but run docker image by using volume, all table disappear, just db.opt remains.

how can i get database's data with using volume?

Answer 1

Your problem it's related on how VOLUMES work, what you are doing it's adding stuff inside /var/lib/mysql at build time, and then when you run the container, a new EMPTY VOLUME is created and linked at the /var/lib/mysql, which pretty much overwrites anything you put there before.

The correct way to go about it for an existing table space would be to create a volume with the docker volume create syntax (ref: https://docs.docker.com/storage/volumes/ ) and then using this trick ( https://github.com/moby/moby/issues/25245#issuecomment-365980572 ) you can add the table data to your volume, and then you run your mariadb container mounting said volume docker run --mount source=myvolume,target=/var/lib/mysql mariadb:latest

I will add that you shouldn't build an image with the tables added at the docker build layer, it makes the docker image huge and it's a wrong use of it all around except for some niche cases like QA databases that you destroy afterwards or read-only databases. The usual way about it it's either using VOLUMES as you stated or with bindings from the host OS.

Then, you shouldn't use mariadb:latest either, choose a particular version and stick with it, as using mariadb:latest can upgrade/downgrade your version and cause all kind of funny bugs.