A stack provides the buildpack lifecycle with build-time and run-time environments in the form of images.
If you’re using the
pack suggest-stackswill display a list of recommended stacks that can be used when running
pack create-builder, along with each stack’s associated build and run images.
Stacks are used by [builders][builder] and are configured through a builder’s configuration file:
[[buildpacks]] # ... [[order]] # ... [stack] id = "com.example.stack" build-image = "example/build" run-image = "example/run" run-image-mirrors = ["gcr.io/example/run", "registry.example.com/example/run"]
By providing the required
[stack] section, a builder author can configure a stack’s ID, build image, and run image
(including any mirrors).
Run image mirrors provide alternate locations for run images, for use during
build with a builder containing run image mirrors,
pack will select a run image
whose registry location matches that of the specified app image (if no registry host is specified in the image name,
DockerHub is assumed). This is useful when publishing the resulting app image (via the
--publish flag or via
docker push), as the app’s base image (i.e. run image) will be located on the same registry as the app image itself,
reducing the amount of data transfer required to push the app image.
In the following example, assuming a builder configured with the example TOML above, the selected run image will be
$ pack build registry.example.com/example/app
while naming the app without a registry specified,
example/app, will cause
example/run to be selected as the app’s
$ pack build example/app
For local development, it’s often helpful to override the run image mirrors in a builder. For this, the
set-run-image-mirrorscommand can be used. This command does not modify the builder, and instead configures the user’s local machine.
To see what run images are configured for a builder, the
inspect-buildercommand can be used.
inspect-builderwill output built-in and locally-configured run images for a given builder, among other useful information. The order of the run images in the output denotes the order in which they will be matched during
To create a custom stack, simply create customized build and run images containing the following information:
||Identifier for the stack||String|
||Identifier for the stack|
||UID of the user specified in the image|
||GID of the user specified in the image|
NOTE: The stack identifier implies compatibility with other stacks of that same identifier. For instance, a custom stack may use
io.buildpacks.stacks.bionicas its identifier so long as it will work with buildpacks that declare compatibility with the
Mixins provide a way to document OS-level dependencies that a stack provides to buildpacks. Mixins can be provided at build-time
(name prefixed with
build:), run-time (name prefixed with
run:), or both (name unprefixed).
When declaring provided mixins, both the build and run image of a stack must contain the following label:
||List of provided mixins||JSON string array|
The following rules apply for mixin declarations:
build:-prefixed mixins may not be declared on a run image
run:-prefixed mixins may not be declared on a build image
io.buildpacks.stack.mixins: ["build:git", "wget"]
io.buildpacks.stack.mixins: ["run:imagemagick", "wget"]
A buildpack must list any required mixins in the
stacks section of its
When validating whether the buildpack’s mixins are satisfied by a stack, the following rules apply:
build:-prefixed mixins must be provided by stack’s build image
run:-prefixed mixins must be provided by stack’s run image
[[stacks]] id = "io.buildpacks.stacks.bionic" mixins = ["build:git", "run:imagemagick", "wget"]
For sample stacks, see our samples repo.
For technical details on stacks, see the platform specification for stacks.