Version 2.3

Customizing Stacks and Buildpacks

Buildpacks are used by Kf to turn an application's source code into an executable image. Cloud Native Buildpacks use the latest Buildpack API v3 and companies including VMware and Heroku are actively adding v3 support to existing buildpacks.

Kf supports Buildpacks conforming to both V2 and V3 of the Buildpack API specification.

Comparison between V2 and V3 buildpacks

V2 Buildpacks V3 Buildpacks
Alternate names Cloud Foundry Buildpacks Cloud Native Buildpacks (CNB), Builder Images
Status Being Replaced Current
Ownership Cloud Foundry Buildpacks.io
Stack Shared by builder and runtime Optionally different for builder and runtime
Local development Not possible Yes, with the pack CLI
Custom buildpacks Available at runtime Must be built into the builder

Buildpack lifecycle

Step Cloud Foundry Kf with Buildpacks V2 Kf with Buildpacks V3
Source location BITS service Container registry Container registry
Buildpack location BOSH/HTTP HTTP Container registry
Stack location BOSH Container registry Container registry
Result Droplet (App binary without stack) Image (Droplet on a stack) Image
Runtime Droplet glued on top of stack and run Run produced image Run produced image

Kf always produces a full, executable image as a result of its build process. Cloud Foundry, on the other hand, produces parts of an executable image at build time and the rest is added at runtime.

Kf chose to follow the model of always producing a full image for the following reasons:

  • Images can be exported, run locally, and inspected statically
  • Better security and auditing with tools like binary authorization
  • App deployments are reproducible

Kf and Buildpacks

Kf stores its global list of buildpacks and stacks in the config-defaults ConfigMap in the kf Namespace. Each Space reflects these buildpacks in its status field. For a Space named buildpack-docs you could run the following to see the full Space configuration:

$ kf space buildpack-docs

Getting Space buildpack-docs
API Version:  kf.dev/v1alpha1
Kind:         Space
Metadata:
  Creation Timestamp:  2020-02-14T15:09:52Z
  Name:                buildpack-docs
  Self Link:           /apis/kf.dev/v1alpha1/spaces/buildpack-docs
  UID:                 0cf1e196-4f3c-11ea-91a4-42010a80008d
Status:
  Build Config:
    Buildpacks V2:
    - Name:      staticfile_buildpack
      URL:       https://github.com/cloudfoundry/staticfile-buildpack
      Disabled:  false
    - Name:      java_buildpack
      URL:       https://github.com/cloudfoundry/java-buildpack
      Disabled:  false
    Stacks V2:
    - Image:  cloudfoundry/cflinuxfs3
      Name:   cflinuxfs3
    Stacks V3:
    - Build Image:  cloudfoundry/cnb:cflinuxfs3
      Description:  A large Cloud Foundry stack based on Ubuntu 18.04
      Name:         org.cloudfoundry.stacks.cflinuxfs3
      Run Image:    cloudfoundry/run:full-cnb

Under the Build Config section there are three fields to look at:

  • Buildpacks V2 contains a list of V2 compatible buildpacks in the order they'll be run
  • Stacks V2 indicates the stacks that can be chosen to trigger a V2 buildpack build
  • Stacks V3 indicates the stacks that can be chosen to trigger a V3 buildpack build

You can also list the stacks with kf stacks:

$ kf stacks

Getting stacks in Space: buildpack-docs
Version  Name                                Build Image                  Run Image                  Description
V2       cflinuxfs3                          cloudfoundry/cflinuxfs3      cloudfoundry/cflinuxfs3
V3       org.cloudfoundry.stacks.cflinuxfs3  cloudfoundry/cnb:cflinuxfs3  cloudfoundry/run:full-cnb  A large Cloud Foundry stack based on Ubuntu 18.04

Because V3 build images already have their buildpacks built-in, you must use kf buildpacks to get the list:

$ kf buildpacks

Getting buildpacks in Space: buildpack-docs
Buildpacks for V2 stacks:
  Name                   Position  URL
  staticfile_buildpack   0         https://github.com/cloudfoundry/staticfile-buildpack
  java_buildpack         1         https://github.com/cloudfoundry/java-buildpack
V3 Stack: org.cloudfoundry.stacks.cflinuxfs3:
  Name                                        Position  Version     Latest
  org.cloudfoundry.jdbc                       0         v1.0.179    true
  org.cloudfoundry.jmx                        1         v1.0.180    true
  org.cloudfoundry.go                         2         v0.0.2      true
  org.cloudfoundry.tomcat                     3         v1.1.102    true
  org.cloudfoundry.distzip                    4         v1.0.171    true
  org.cloudfoundry.springboot                 5         v1.1.2      true
  ...

Customizing V3 Buildpacks

You can customize the buildpacks that are available to your developers by creating your own builder image with exactly the buildpacks they should have access to. You can also use builder images published by other authors.

Use a third-party builder image

A list of published CNB stacks is available from the Buildpack CLI pack. As of this writing, pack suggest-stacks outputs:

$ pack suggest-stacks

Stacks maintained by the community:

    Stack ID: heroku-18
    Description: The official Heroku stack based on Ubuntu 18.04
    Maintainer: Heroku
    Build Image: heroku/pack:18-build
    Run Image: heroku/pack:18

    Stack ID: io.buildpacks.stacks.bionic
    Description: A minimal Cloud Foundry stack based on Ubuntu 18.04
    Maintainer: Cloud Foundry
    Build Image: cloudfoundry/build:base-cnb
    Run Image: cloudfoundry/run:base-cnb

    Stack ID: org.cloudfoundry.stacks.cflinuxfs3
    Description: A large Cloud Foundry stack based on Ubuntu 18.04
    Maintainer: Cloud Foundry
    Build Image: cloudfoundry/build:full-cnb
    Run Image: cloudfoundry/run:full-cnb

    Stack ID: org.cloudfoundry.stacks.tiny
    Description: A tiny Cloud Foundry stack based on Ubuntu 18.04, similar to distroless
    Maintainer: Cloud Foundry
    Build Image: cloudfoundry/build:tiny-cnb
    Run Image: cloudfoundry/run:tiny-cnb

To modify Kf to use the stack published by Heroku, edit the config-defaults ConfigMap in the kf Namespace. Add an entry to the spaceStacksV3 key like the following:

$ kubectl edit configmap config-defaults -n kf

spaceStacksV3: |
  - name: org.cloudfoundry.stacks.cflinuxfs3
    description: A large Cloud Foundry stack based on Ubuntu 18.04
    buildImage: cloudfoundry/cnb:cflinuxfs3
    runImage: cloudfoundry/run:full-cnb
  - name: heroku-18
    description: The official Heroku stack based on Ubuntu 18.04
    buildImage: heroku/pack:18-build
    runImage: heroku/pack:18

Then, run stacks again:

$ kf stacks

Getting stacks in Space: buildpack-docs
Version  Name                                Build Image                  Run Image                  Description
V2       cflinuxfs3                          cloudfoundry/cflinuxfs3      cloudfoundry/cflinuxfs3
V3       org.cloudfoundry.stacks.cflinuxfs3  cloudfoundry/cnb:cflinuxfs3  cloudfoundry/run:full-cnb  A large Cloud Foundry stack based on Ubuntu 18.04
V3       heroku-18                           heroku/pack:18-build         heroku/pack:18             The official Heroku stack based on Ubuntu 18.04

Create your own builder image

The Buildpack CLI pack is used to create your own builder image. You can follow pack's Working with builders using create-builder documentation to create your own builder image. Once created, push it to a container registry and use add it to the config-defaults ConfigMap.

Setting a default stack

Apps will be assigned a default stack if one isn't supplied in their manifest. The default stack is the first in the V2 or V3 stacks list. Unless overridden, a V2 stack is chosen for compatibility with Cloud Foundry.

You can force Kf to use a V3 stack instead of a V2 by setting the spaceDefaultToV3Stack field in the config-defaults ConfigMap in the kf Namespace to be "true":

$ kubectl edit configmap config-defaults -n kf

spaceDefaultToV3Stack: "true"

This option can also be modified on a per-Space basis by changing setting the spec.buildConfig.defaultToV3Stack field to be true or false. If unset, the value from the config-defaults ConfigMap is used.

config-defaults value for spaceDefaultToV3Stack Space's spec.buildConfig.defaultToV3Stack Default stack
unset unset V2
"false" unset V2
"true" unset V3
any false V2
any true V3