Docker for Windows: cannot write on shared volumes

[rahonalab]

as already mentioned here #95 , mariadb container on windows cannot write its database files on a shared volume. Here is a snippet of my docker-compose.yaml

sql:
    image: mariadb
    env_file: ./secrets.env
    domainname: ${DOMAINNAME}
    hostname: ${FIRSTNAME}-sql
    volumes:
      - ./${FIRSTNAME}-container/lib/mysql:/var/lib/mysql
  web:
   image: rahonabe/icinga2-web
   env_file: ./secrets.env
   links:
     - sql
     - core
   domainname: ${DOMAINNAME}
   hostname: ${FIRSTNAME}-web
   build: 
    context: ./web
   ports:
     - 80:80
   volumes:
     - ./${FIRSTNAME}-container/etc/icingaweb2:/etc/icingaweb2
     - ./${FIRSTNAME}-container/webroot_icingaweb2:/usr/share/icingaweb2
     - ./${FIRSTNAME}-container/webroot_nagvis:/usr/local/nagvis
     - ./${FIRSTNAME}-container/lib/php5/sessions:/var/lib/php5/sessions
     - ./${FIRSTNAME}-container/log/apache2:/var/log/apache2
     - ./${FIRSTNAME}-container/certs:/etc/apache2/ssl:ro
     - ./${FIRSTNAME}-container/perfdata:/var/lib/pnp4nagios/perfdata
     - ./${FIRSTNAME}-container/etc/pnp4nagios:/etc/pnp4nagios
   volumes_from:
     - core
     - sql

[yosifkit]

The only solution on Docker for Windows is to use a Docker controlled volume, rather than mapping it to your host. And it will still work to share volumes to other containers. (see also, the named volumes conversation here)

version: '3.4'

services:
  sql:
    image: mariadb
    env_file: ./secrets.env
    domainname: ${DOMAINNAME}
    hostname: ${FIRSTNAME}-sql
    volumes:
      - sql-data:/var/lib/mysql

volumes:
  sql-data:

[rahonalab]

Thank you, I am still confused about Docker volumes and I didn’t get your point. Now it’s clearer, but will data be maintained if the container is deleted?

[yosifkit]

@rahonalab, yes the named volume has a life-cycle independent of the container. If you do docker-compose stop and docker-compose rm, then the volume will stick around as sql-data. docker volume ls will let you see ones that are still around (which may be quite a few unused ones) You can get rid of all volumes not currently used by a container with docker volume prune (only while your sql container is running, otherwise your volume will be removed)

[rahonalab]

thank you @yosifkit
I used to develop and run my docker containers in unix environments (mac os and linux) and I am pretty new to docker in windows environments. If I understand it right, docker controlled volumes are more agnostic/universal with respect to the hosting system; mapped volumes worked just fine for me in unix environments, since I can change file attributes without logging into the container, but I see that on windows things are a little bit different.

[wglambert]

These seem related to docker-on-windows/mac:
docker-library/mongo#235 (comment)
docker-library/postgres#439 (comment)

Because they use virtualbox there is an issue with sharing folders between the host and container.
See https://www.virtualbox.org/ticket/819

Since the issue seems resolved I'm going to close.
If you believe this to be in error then let me know and I'll re-open it