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Buildpack api changes to support phase 1 of Dockerfiles implementation
Signed-off-by: Natalie Arellano <narellano@vmware.com>
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| # Image Extension Interface Specification | ||
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| This document specifies the interface between a lifecycle program and one or more image extensions. | ||
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| The lifecycle program uses image extensions to generate Dockerfiles that can be used to select the runtime base image prior to buildpack builds. | ||
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| ## Table of Contents | ||
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| <!-- Using https://github.com/yzhang-gh/vscode-markdown to manage toc --> | ||
| - [Image Extension Interface Specification](#image-extension-interface-specification) | ||
| - [Table of Contents](#table-of-contents) | ||
| - [Image Extension API Version](#image-extension-api-version) | ||
| - [Image Extension Interface](#image-extension-interface) | ||
| - [Detection](#detection) | ||
| - [Generation](#generation) | ||
| - [Phase: Generation](#phase-generation) | ||
| - [Purpose](#purpose) | ||
| - [Process](#process) | ||
| - [Dockerfile Requirements](#dockerfile-requirements) | ||
| - [Data Format](#data-format) | ||
| - [Files](#files) | ||
| - [extension.toml (TOML)](#extensiontoml-toml) | ||
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| ## Image Extension API Version | ||
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| This document accompanies Buildpack API version `0.9`. | ||
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| ## Image Extension Interface | ||
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| Unless otherwise noted, image extensions are expected to conform to the [Buildpack Interface Specification](buildpack.md). | ||
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| ### Detection | ||
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| Executable: `/bin/detect`, Working Dir: `<app[AR]>` | ||
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| Image extensions participate in the buildpack [detection](buildpack.md#detection) process, with the same interface for `/bin/detect`. However: | ||
| - Detection is optional for image extensions, and they are assumed to pass detection when `/bin/detect` is not present. | ||
| - Image extensions MUST only output `provides` entries to the build plan. They MUST NOT output `requires`. | ||
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| ### Generation | ||
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| Executable: `/bin/generate`, Working Dir: `<app[AR]>` | ||
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| Image extensions participate in a generation process that is similar to the buildpack [build](buildpack.md#build) process, with an interface that is similar to `/bin/build`. However: | ||
| - Image extensions' `/bin/generate` MUST NOT write to the app directory. | ||
| - Instead of the `CNB_LAYERS_DIR`, image extensions receive a `CNB_OUTPUT_DIR` which MUST be the absolute path of an `<output>` directory and MUST NOT be the path of the buildpack layers directory. | ||
| - If an image extension is missing `/bin/generate`, the image extension root MUST be treated as a pre-populated `<output>` directory. | ||
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| ## Phase: Generation | ||
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| ### Purpose | ||
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| The purpose of the generation phase is to generate Dockerfiles that can be used to select the runtime base image. | ||
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| ### Process | ||
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| **GIVEN:** | ||
| - The final ordered group of image extensions determined during the detection phase, | ||
| - A directory containing application source code, | ||
| - The Buildpack Plan, | ||
| - An `<output>` directory used to store generated artifacts, | ||
| - A shell, if needed, | ||
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| For each image extension in the group in order, the lifecycle MUST execute `/bin/generate`. | ||
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| 1. **If** the exit status of `/bin/generate` is non-zero, \ | ||
| **Then** the lifecycle MUST fail the build. | ||
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| 2. **If** the exit status of `/bin/generate` is zero, | ||
| 1. **If** there are additional image extensions in the group, \ | ||
| **Then** the lifecycle MUST proceed to the next image extension's `/bin/generate`. | ||
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| 2. **If** there are no additional image extensions in the group, \ | ||
| **Then** the lifecycle MUST proceed to the build phase. | ||
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| For each `/bin/generate` executable in each image extension, the lifecycle: | ||
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| - MUST provide path arguments to `/bin/generate` as described in the [generation](#generation) section. | ||
| - MUST configure the build environment as described in the [Environment](buildpack.md#environment) section. | ||
| - MUST provide all `<plan>` entries that were required by any buildpack in the group during the detection phase with names matching the names that the image extension provided. | ||
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| Correspondingly, each `/bin/generate` executable: | ||
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| - MAY read from the `<app>` directory. | ||
| - MUST NOT write to the `<app>` directory. | ||
| - MAY read the build environment as described in the [Environment](buildpack.md#environment) section. | ||
| - MAY read the Buildpack Plan. | ||
| - MAY log output from the build process to `stdout`. | ||
| - MAY emit error, warning, or debug messages to `stderr`. | ||
| - MAY write a run.Dockerfile to the `<output>` directory. This file MUST adhere to the requirements listed below. | ||
| - MUST NOT write SBOM (Software-Bill-of-Materials) files as described in the [Software-Bill-of-Materials](#software-bill-of-materials) section. | ||
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| #### Dockerfile Requirements | ||
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| run.Dockerfiles: | ||
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| - MAY contain a single `FROM` instruction | ||
| - MUST NOT contain any other instructions | ||
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| ## Data Format | ||
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| ### Files | ||
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| ### extension.toml (TOML) | ||
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| This section describes the 'Extension descriptor'. | ||
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| ```toml | ||
| api = "<buildpack API version>" | ||
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| [extension] | ||
| id = "<extension ID>" | ||
| name = "<extension name>" | ||
| version = "<extension version>" | ||
| homepage = "<extension homepage>" | ||
| description = "<extension description>" | ||
| keywords = [ "<string>" ] | ||
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| [[extension.licenses]] | ||
| type = "<string>" | ||
| uri = "<uri>" | ||
| ``` | ||
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| Image extension authors MUST choose a globally unique ID, for example: "io.buildpacks.apt". | ||
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| The image extension `id`, `version`, `api`, `licenses`, and `sbom-formats` entries MUST follow the requirements defined in the [Buildpack Interface Specification](buildpack.md). |