Stack association in Cloud Foundry buildpacks

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Learn about the stack association feature for your Cloud Foundry buildpacks.

To avoid security exposure, verify that you migrate your apps and custom buildpacks to use the cflinuxfs4 stack based on Ubuntu 22.04 LTS (Jammy Jellyfish). The cflinuxfs3 stack is based on Ubuntu 18.04 (Bionic Beaver), which reaches end of standard support in April 2023.

Stack association

Each buildpack in your deployment is associated with a stack. When you run cf buildpacks, you can see this in the stack column for each buildpack.

For example:

$ cf buildpacks
Getting buildpacks...

position   name                                stack        enabled   locked   filename
1          staticfile_buildpack                cflinuxfs3   true      false    staticfile_buildpack-cached-cflinuxfs3-v1.5.36.zip
2          java_buildpack                      cflinuxfs3   true      false    java_buildpack-cached-cflinuxfs3-v4.53.zip
3          ruby_buildpack                      cflinuxfs3   true      false    ruby_buildpack-cached-cflinuxfs3-v1.9.0.zip
. . .
12         ruby_buildpack                      cflinuxfs4   true      false    ruby_buildpack-cached-cflinuxfs4-v1.9.0.zip
13         dotnet_core_buildpack               cflinuxfs4   true      false    dotnet-core_buildpack-cached-cflinuxfs4-v2.4.5.zip
. . .

Because of the stack association, buildpacks do not have to be uniquely named. This helps in managing similar buildpacks that are compatible with different stacks.

The buildpack packager includes a -stack option. If you use this option and upload a buildpack, the Cloud Controller detects the stack association, and creates a stack record for the buildpack.

Missing stack record in buildpacks

Some buildpacks might have a missing stack record, if for example, you uploaded a custom buildpack before Cloud Foundry introduced stack association. The output of cf buildpacks shows a blank stack column if the buildpack does not have a stack record.

In this case, you must manually assign a stack to the buildpack. To do this, run:

cf update-buildpack BUILDPACK-NAME --assign-stack stack

Buildpacks with a missing stack record continue to work, but are more manageable when the stack record is present.

If you push apps to a deployment that has buildpacks with a missing stack record, the following might occur:

• If you push an app and specify a stack with cf push app-name -s stack, Cloud Foundry uses that stack. Otherwise, it uses the system default, cflinuxfs4.
• You might see additional logging in the buildpack detection output of the cf push command when Cloud Foundry detects buildpacks without a stack record.

Managing stack association with the cf CLI

The cf CLI commands for managing buildpacks include functionality to support association between buildpacks and stacks. The update-buildpack, rename-buildpack, and delete-buildpack commands all include a -s flag for specifying a stack.

The cf CLI v7 command removes the cf rename-buildpack command in favor of a --rename option for cf update-buildpack.

When using buildpacks with the cf CLI, consider the following:

• You cannot upload a buildpack with cf create-buildpack if a buildpack of the same name already exists and has a missing stack record.
• When using cf create-buildpack, you might inadvertently create a duplicate buildpack with a nil stack. cf create-buildpack does not prevent creation of buildpacks with no stack association.
• The -s flag is required when there are buildpacks with the same name. If you are working on a uniquely named buildpack, you do not need to specify its stack.
• If you have buildpacks of the same name, one with a stack record and one without, run cf CLI commands without the -s flag on the buildpack with the missing stack record.

Scenario examples

See the following examples for managing buildpacks with the cf CLI. These examples are applicable when running cf update-buildpack or cf delete-buildpack:

• Updating or deleting a uniquely-named buildpack:
  • You have a single buildpack named my-buildpack, and it is associated with stack_a. To delete the buildpack, run cf delete-buildpack my-buildpack. You can also provide -s stack_a, but the option is not required if you have a uniquely-named buildpack.
• Updating or deleting a uniquely-named buildpack that has a nil stack:
  • You have a single buildpack named my-buildpack, and it is not associated with a stack. To delete the buildpack, run cf delete-buildpack my-buildpack.
• Updating or deleting a buildpack when another buildpack exists with the same name. Both buildpacks have stack associations:
  • You have two buildpacks named my-buildpack, one that is associated with stack_a and the other associated with stack_b. To delete the buildpack that uses stack_a, run cf delete-buildpack my-buildpack -s stack_a.
• Updating or deleting a buildpack when another buildpack exists with the same name. One buildpack has a stack association, and the other buildpack has a nil stack:
  • You have two buildpacks named my-buildpack, one associated with stack_a and the other with no (nil) stack association:
    • To delete the buildpack that uses stack_a, run cf delete-buildpack my-buildpack -s stack_a.
    • To delete the buildpack that is associated with the nil stack, run cf delete-buildpack my-buildpack.