Microservices Impact — CI Broadcast

When a provider service changes its API, consumer services need to know which of their files and lines reference the broken endpoints or types.

drift-guard implements this with a CI broadcast pattern: the provider generates a diff JSON and notifies consumers via repository_dispatch. Each consumer scans itself independently.

Provider PR opened
       │
       ▼
┌──────────────────────────────────────────┐
│  drift-guard detects breaking changes    │
│  → uploads diff.json artifact            │
│  → sends repository_dispatch to          │
│    service-b, service-c, service-d       │
└──────────────────────────────────────────┘
       │           │           │
       ▼           ▼           ▼
  service-b    service-c    service-d
  scans ./src  scans ./src  scans ./src
  posts hits   posts hits   no hits
  to own PR    to own PR

Provider setup

In the provider service, add upload-diff, notify-consumers, and notify-token to the drift-guard action:

# .github/workflows/api-drift.yml (provider service)
name: API Drift Check

on:
  pull_request:

permissions:
  contents: write
  pull-requests: write
  issues: write

jobs:
  drift:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - uses: pgomes13/drift-guard-engine@v1
        with:
          upload-diff: "true"
          notify-consumers: "org/service-b,org/service-c"
          notify-token: ${{ secrets.CONSUMER_DISPATCH_TOKEN }}

CONSUMER_DISPATCH_TOKEN must be a GitHub PAT (or fine-grained token) with contents: write on each consumer repo.

Consumer setup

Each consumer service adds a workflow that fires on repository_dispatch:

# .github/workflows/impact-check.yml (consumer service)
name: Impact Check

on:
  repository_dispatch:
    types: [drift-guard-impact]

permissions:
  pull-requests: write
  issues: write

jobs:
  impact:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: pgomes13/drift-guard-engine/action/impact-check@v1
        with:
          diff-json: ${{ toJson(github.event.client_payload.diff) }}
          scan-dir: "./src"
          format: "markdown"
          fail-on-hits: "false"

How the consumer notifies the team

The action handles three situations automatically:

Consumer state	What happens
Has open PR(s)	Impact report posted as a PR comment on every open PR
No open PRs	A GitHub Issue is opened (or updated) with the full impact report and a drift-guard label
No hits found	Nothing posted — job exits cleanly

This means the team is always notified, whether or not they have work in progress.

Note: issues: write is required for both PR comments (GitHub's PR comment API uses the Issues endpoint) and for opening issues.

Artifact-only mode (no dispatch)

If you prefer polling over push, consumers can download the diff artifact directly instead of using repository_dispatch:

# Consumer — polls provider artifact instead of dispatch
- uses: pgomes13/drift-guard-engine/action/impact-check@v1
  with:
    provider-repo: "org/user-service"
    scan-dir: "./src"
    token: ${{ secrets.PROVIDER_READ_TOKEN }}

PROVIDER_READ_TOKEN needs actions:read on the provider repo.

Impact check inputs

Input	Description	Default
provider-repo	Provider repo to download artifact from	—
diff-json	Inline JSON diff (from repository_dispatch payload)	—
scan-dir	Directory to scan for source references	.
format	Output format: text, json, markdown, github	github
fail-on-hits	Exit 1 if any references found	false
token	Token with actions:read on provider repo	GITHUB_TOKEN

Provider action inputs

Input	Description	Default
upload-diff	Upload diff JSON as drift-guard-diff artifact	false
notify-consumers	Comma-separated list of repos to notify	—
notify-token	Token with contents:write on consumer repos	—