Mounting Volumes

Volumes are a mechanism for both supplying and persisting data generated by build containers.

Mounting Volumes (--volume)

The --volume parameter must be one of the following:

  • A volume mount.
  • A comma separated list of volume mounts.

Each volume mount has the following format:

<host path>:<target path>[:<mode>]
<host path>

This is the name of the volume, it is unique on a given host machine.

<target path>

The path where the file or directory is available in the container.


An optional comma separated list of mount options. If no options are provided, the read-only option will be used. A mount option must be one of the following:

  • ro, volume contents are read-only.
  • rw, volume contents are readable and writeable.
  • volume-opt=key=value, can be specified more than once, takes a key-value pair consisting of the option name and its value.


For the following examples we will use our samples repo for simplicity.

Here we bind mount a local folder into our container and display its contents during a pack build.

Linux container example

We’ll create a new docker volume:

docker volume create test-volume

Next, we’ll create a text file on the volume:

docker run --rm \
    --volume test-volume:/tmp/volume:rw \
    bash \
    bash -c 'echo "Hello from a volume!" > /tmp/volume/volume_contents.txt'

Now, we can mount this volume during pack build:

ls -al
pack build volume-example \
    --builder cnbs/sample-builder:bionic \
    --buildpack samples/buildpacks/hello-world \
    --path samples/apps/bash-script \
    --volume test-volume:/platform/volume:ro

The above pack build ... command will mount the test-volume volume in the /platform directory of the container.

Since we are using the samples/hello-world buildpack, we should see the /platform directory files listed:

[builder]      platform_dir files:
[builder]        /platform/volume:
[builder]        total 12
[builder]        drwxr-xr-x 2 root root 4096 Sep 17 20:17 .
[builder]        drwxr-xr-x 1 root root 4096 Sep 17 20:18 ..
[builder]        -rw-r--r-- 1 root root   21 Sep 17 20:18 volume_contents.txt