The extender applies Dockerfiles output by image extensions to the build or runtime base image.

Exit Codes

When extending the build image:

• In addition to the outputs enumerated below, outputs produced by extender include those produced by builder - as the lifecycle will run the build phase after extending the build image.
• Platforms MUST skip the builder and proceed to the exporter.

Exit Code	Result
0	Success
11	Platform API incompatibility error
12	Buildpack API incompatibility error
1-10, 13-19	Generic lifecycle errors
100-109	Extension-specific lifecycle errors

• For each extension in <group> in order, if a Dockerfile exists in <generated>/<buildpack-id>/<kind>.Dockerfile, the lifecycle:
  • Shall apply the Dockerfile to the environment according to the process outlined in the Image Extension Specification.
  • SHALL set the build context to the folder according to the process outlined in the Image Extension Specification.
• The extended image must be an extension of:
  • The build-image in <analyzed> when <kind> is build, or
  • The run-image in <analyzed> when <kind> is run
• When extending the build image, after all build.Dockerfiles are applied, the lifecycle:
  • Shall proceed with the build phase using the provided <gid> and <uid>
• When extending the run image, after all run.Dockerfiles are applied, the lifecycle:
  • If any run.Dockerfile set the label io.buildpacks.rebasable to false or left the label unset:
    • Shall set the label io.buildpacks.rebasable to false on the extended run image
  • If after the final run.Dockerfile the run image user is root,
    • Shall fail
  • Shall copy the manifest and config for the extended run image, along with any new layers, to <extended>/run

---

For more information about the extender, see the Platform API spec.

---