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  
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. 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

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