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Docker Container Can't See Host Files? Anonymous Volume Overrides Bind Mount

Β· 3 min read
CCLEE
CCLEE

Encountered this issue while deploying a WordPress site for a client. Here's the root cause and solution.

TL;DR​

The VOLUME declaration in an image's Dockerfile creates anonymous volumes with higher mount priority than docker-compose.yml bind mounts. Solution: Stop container β†’ Delete anonymous volume β†’ Restart.

Problem​

After CI deployment, new static files or PHP code don't exist inside the container:

  • assets/images/logo.png exists on host, missing in container β†’ Logo doesn't display
  • inc/setup.php has new filter code, container has old version β†’ Filter doesn't work
  • Files updated after git pull, container still has old content

Root Cause​

WordPress official image's Dockerfile includes:

VOLUME /var/www/html

Even if your docker-compose.yml configures bind mount:

volumes:
  - ./wordpress/wp-content:/var/www/html/wp-content

Docker still creates an anonymous volume for the VOLUME declared path. Anonymous volumes have higher mount priority than bind mounts, causing:

  1. /var/www/html is taken over by anonymous volume
  2. Your bind mount targets /var/www/html/wp-content
  3. But the anonymous volume already "occupies" the parent directory, bind mount gets overridden

Verify with docker inspect:

docker inspect prod_wordpress --format '{{range .Mounts}}{{.Type}}: {{.Source}} -> {{.Destination}}{{"\n"}}{{end}}'

Output similar to:

volume: /var/lib/docker/volumes/wp-prod_wp_html/_data -> /var/www/html  # Anonymous volume!
bind: /var/www/wp-prod/wordpress/wp-content -> /var/www/html/wp-content

Solution​

# 1. Stop containers
cd /var/www/wp-prod && docker compose down

# 2. Delete anonymous volume
docker volume rm wp-prod_wp_html

# 3. Restart
docker compose up -d

Verification​

docker inspect prod_wordpress --format '{{range .Mounts}}{{.Type}}: {{.Source}} -> {{.Destination}}{{"\n"}}{{end}}'

Should only show bind mount, no anonymous volume:

bind: /var/www/wp-prod/wordpress/wp-content -> /var/www/html/wp-content

Prevention​

When using bind mount deployment, check if the image declares VOLUME. If declared:

  1. Before first start, confirm no residual anonymous volumes exist
  2. Or modify docker-compose.yml to make bind mount path match VOLUME path (mount to same level)

After fixing, git pull updates are automatically read by the containerβ€”no docker cp or container restart needed.

Important

  • Backup data before deleting anonymous volumes or ensure it can be restored via git pull
  • Test in staging environment before production operations
  • If container has critical data, backup with docker cp first
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