Standard Action

for Standard & Paisano.

Don't waste any time on extra work. Use Standard Action to automatically detect CI targets that need re-doing; implemented on top of familiar GH Actions.

Features

Evaluate once and distribute final build instructions to workers
Once configured, discovery picks up new targets automatically
Optional proviso script can detect if work needs to be done

Note on proviso: one example is the oci block type which checks if the image is already in the registry and only schedules a build if its missing. If proviso queries private remote state then the discovery environment must provide all authentication prior to running the discovery step.

Usage

Minimumn nix version v2.16.1

Tip! Since GitHub CI doesn't support yaml anchors, explode your file with:

yq '. | explode(.)' ci.raw.yaml > ci.yaml

Standalone

{
  /* ... */
  outputs = {std, ...}@inputs: std.growOn {
  /* ... */
    cellBlocks = with std.blockTypes; [
      (installables "packages" {ci.build = true;})
      (containers "oci-images" {ci.publish = true;})
      (kubectl "deployments" {ci.apply = true;})
    ];
  /* ... */
  };
}

GH Action file

# yq '. | explode(.)' this.yml > .github/workflows/std.yml
name: CI/CD

on:
  pull_request:
    branches:
      - main
  push:
    branches:
      - main

permissions:
  id-token: write
  contents: read

concurrency:
  group: std-${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

jobs:
  discover:
    outputs:
      hits: ${{ steps.discovery.outputs.hits }}
    runs-on: ubuntu-latest
    steps:
      # Important: use v25 or above as it also detects flake configuration
      - uses: nixbuild/nix-quick-install-action@master
      # if you want to use nixbuild
      - uses: nixbuild/nixbuild-action@v17
        with:
          nixbuild_ssh_key: ${{ secrets.SSH_PRIVATE_KEY }}
          generate_summary_for: job
      # significantly speeds up things in small projects
      - uses: DeterminateSystems/magic-nix-cache-action@main
      - uses: divnix/std-action/discover@main
        id: discovery

  build: &job
    needs: discover
    name: ${{ matrix.target.jobName }}
    runs-on: ubuntu-latest
    if: fromJSON(needs.discover.outputs.hits).packages.build != '{}'
    strategy:
      matrix:
        target: ${{ fromJSON(needs.discover.outputs.hits).packages.build }}
    steps:
      # Important: use v25 or above as it also detects flake configuration
      - uses: nixbuild/nix-quick-install-action@master
      # if you want to use nixbuild
      - uses: nixbuild/nixbuild-action@v17
        with:
          nixbuild_ssh_key: ${{ secrets.SSH_PRIVATE_KEY }}
          generate_summary_for: job
      - uses: DeterminateSystems/magic-nix-cache-action@main
      - uses: divnix/std-action/run@main

  images:
    <<: *job
    needs: [discover, build]
    if: fromJSON(needs.discover.outputs.hits).oci-images.publish != '{}'
    strategy:
      matrix:
        target: ${{ fromJSON(needs.discover.outputs.hits).oci-images.publish }}

  deploy:
    <<: *job
    needs: [discover, images]
    environment:
      name: development
      url: https://my.dev.example.com
    if: fromJSON(needs.discover.outputs.hits).deployments.apply != '{}'
    strategy:
      matrix:
        target: ${{ fromJSON(needs.discover.outputs.hits).deployments.apply }}

Persistent Discovery Host

Requirements

nix >= v2.16.1
zstd
(gnu) parallel
jq
base64
bash > v5

The persistent host must also implement the nixConfig detection capabilities implemented by this script.

{
  /* ... */
  outputs = {std, ...}@inputs: std.growOn {
  /* ... */
    cellBlocks = with std.blockTypes; [
      (devshells "envs" {ci.build = true;})
      (containers "oci-images" {ci.publish = true;})
    ];
  /* ... */
  };
}

GH Action file

# yq '. | explode(.)' this.yml > .github/workflows/std.yml
name: CI/CD

on:
  pull_request:
    branches:
      - main
  push:
    branches:
      - main

env:
  DISCOVERY_USER_NAME: gha-runner
  DISCOVERY_KNOWN_HOSTS_ENTRY: "10.10.10.10 ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIEOVVDZydvD+diYa6A3EtA3WGw5NfN0wv7ckQxa/fX1O"

permissions:
  id-token: write
  contents: read

concurrency:
  group: ${{ github.sha }}
  cancel-in-progress: true

jobs:
  discover:
    outputs:
      hits: ${{ steps.discovery.outputs.hits }}
    runs-on: [self-hosted, discovery]
    steps:
      - name: Standard Discovery
        uses: divnix/std-action/discover@main
        id: discovery
        # avoids transporting derivations via GH Cache
        with: { ffBuildInstructions: true }

  image: &run-job
    needs: discover
    strategy:
      fail-fast: false
      matrix:
        target: ${{ fromJSON(needs.discover.outputs.hits).oci-images.publish }}
    if: fromJSON(needs.discover.outputs.hits).oci-images.publish != '{}'
    name: ${{ matrix.target.jobName }}
    runs-on: ubuntu-latest
    steps:
      # sets up ssh credentials for `ssh discovery ...`
      - uses: divnix/std-action/setup-discovery-ssh@main
        with:
          ssh_key: ${{ secrets.SSH_PRIVATE_KEY_CI }}
          user_name: ${{ env.DISCOVERY_USER_NAME }}
          ssh_known_hosts_entry: ${{ env.DISCOVERY_KNOWN_HOSTS_ENTRY }}
      - uses: divnix/std-action/run@main
        # avoids retreiving derivations via GH Cache and uses `ssh discovery ...` instead
        with: { ffBuildInstructions: true }

  build:
    <<: *run-job
    strategy:
      matrix:
        target: ${{ fromJSON(needs.discover.outputs.hits).envs.build }}
    if: fromJSON(needs.discover.outputs.hits).envs.build != '{}'

Notes & Explanation

Notes on the Build Matrix

Hits from the discovery phase are namespaced by Block and Action.

That means:

In: target: ${{ fromJSON(needs.discover.outputs.hits).packages.build }}
- packages is the name of a Standard Block
- build is the name of an Action of that Block

Debugging

Watch out for base64-encoded blobs in the logs, you can inspect the working data of that context by doing: base64 -d <<< copy-blob-here | jq.