The docker-compose file https://docs.docker.com/compose/compose-file/#/volumes-volume-driver shows various ways to mount host sub-directories relative to the compose file.
For example:
volumes:
# Just specify a path and let the Engine create a volume
- /var/lib/mysql
# Specify an absolute path mapping
- /opt/data:/var/lib/mysql
# Path on the host, relative to the Compose file
- ./cache:/tmp/cache
# User-relative path
- ~/configs:/etc/configs/:ro
# Named volume
- datavolume:/var/lib/mysql
Is is possible to mount a sub-directory of a named volume at a specific location? For example something like below, which I tried, but does not seem to work.
# Named volume
- datavolume/sql_data:/var/lib/mysql
I am assuming I might be able to manage this by mounting the data volume to a location like /data and then in the Dockerfiles for each container, create symbolic links from the sub-directories to the locations.
for example in a docker-compose.yml file
volumes:
- datavolume:/data
and then in the container Dockerfile
RUN ln -s /data/sql_data /var/lib/mysql
I started going down this path but it was getting messy and was not working. Before I either abandon that approach or invest the time debugging it, I wanted to make sure there was no way to just specify sub-directories of a named vollume.
4
2023: As noted by Michael Bolli in the comments, that feature is now a work-in-progress:
PR 45687: “volumes: Implement subpath mount”
Make it possible to mount subdirectory of a named volume.
Q1 2024: this is merged! Commit 31ccdbb.
Possibly for Moby 26.0.
March 2024, as mentioned in issue 32582:
CLI already supports it (starting from v26.0.0-rc1):
docker/cliPR #4331(and you can already install it from the
testchannel)Compose support is still WIP (it needs to move to v26 first).
March 2024: Paweł Gronowski confirms in the same issue:
moby v26.0.0 is released, so you can already try out this feature.
2016: No because compose/config/config.py#load(config_details) check if datavolume/sql_data matches a named volume (in compose/config/validation.py#match_named_volumes()).
datavolume would, datavolume/sql_data would not.
As memetech points out in the comments, the is an issue tracking this since April 2017:
moby/moby issue 32582: “[feature] Allow mounting sub-directories of named volumes“.
In that issue, Joohansson adds (see comment)
In the meantime, I use this workaround to mount the whole volume on a separate path and then symlink it to the sub path.
# In the Dockerfile: RUN mkdir -p /data/subdir RUN ln -s /data/subdir /var/www/subdirThen mount the volume as normal.
The/subdirmust exist in the volume.docker run -d -v myvol:/data mycontainerNow anything read or written by the webserver will be stored in the volume
subdirand can’t access the other data.
5
It is not possible.
You can just create normal sub directories into the volume and then in your application link or configure to use that path.
Let’s say you use this compose volume definition :
volumes:
- myVolume:/mnt/data
volumes:
myVolume:
The volume setup is irrelevant, but only the mounpoint matters, assuing the mount point inside container is “/mnt/data/”
Then in you application just point to sub directories:
logging to /mnt/data/log,
database files to /mnt/data/db
configs to /mnt/config
For example doing this in DockeFile
RUN mkdir -p /mnt/data/log
RUN mkdir /mnt/data/db
RUN mkdir /mnt/data/config
RUN sed ... to change logging path to /mnt/data/log
RUN mv /current/db/data/files /mnt/data/db
RUN ln /mnt/data/db /current/db/data/files
...