Customize 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. Companies are actively adding v3 support to existing buildpacks.

Kf supports buildpacks that conform to both V2 and V3 of the Buildpack API specification.

Compare 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. Modification of the buildpacks and stacks properties should be done at the kfsystem Custom Resource, the Kf operator automatically updates the config-defaults ConfigMap based on the values set at kfsystem.

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
  ...

Customize 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 kfsystem Custom Resource, which automatically updates the config-defaults ConfigMap in the kf Namespace. Add an entry to the spaceStacksV3 key like the following:

kubectl edit kfsystem kfsystem
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. After it's created, push it to a container registry and add it to the kfsystem Custom Resource.

Set 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 kfsystem Custom Resource to be "true" (kfsystem automatically updates corresonding spaceDefaultToV3Stack field in the config-defaults ConfigMap):

kubectl edit kfsystem kfsystem
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

What's next

Deploy an application