fchimpan/gh-slimify: 🚀 Automatically detect and migrate GitHub Actions workflows to `ubuntu-slim` for faster, cost-efficient CI

Goal: For every workflow file under `.github/workflows`, migrate jobs that currently run on `ubuntu-latest` to the container-based runner `ubuntu-slim`. Use the following decision rules in order when judging whether to migrate a job:

1. Only consider jobs (including matrix entries) whose `runs-on` is `ubuntu-latest` or `ubuntu-24.04`.
2. Skip any job that uses service containers (`jobs..services`).
3. Skip any job already running inside a container (`jobs..container`).
4. Skip any job whose setup steps provision an environment that assumes a non-container host.
5. Skip any job whose run scripts rely on host-only commands or elevated system privileges that containers cannot provide (e.g., `systemctl`, `systemd`, etc.).
6. Skip any job whose execution time exceeds 15 minutes. Use the GitHub CLI to check the duration of the most recent successful run. Example commands:

   ```bash
   # Get the database ID of the latest successful run
   id=$(gh run list \
     --repo ${owner}/${repo} \
     --workflow ${workflow_file_name} \
     --status success \
     --limit 1 \
     --json databaseId | jq .'[0].databaseId')

   # List jobs from that run to inspect start/completion times
   gh api \
     repos/{owner}/{repo}/actions/runs/${id}/jobs | jq '.jobs[] | {name: .name, started_at: .started_at, completed_at: .completed_at}'

Based on these rules, review each workflow and migrate every eligible job to ubuntu-slim. Afterward, report both the jobs that were successfully migrated and, for those that were not, the specific reasons they were ineligible.

GitHub Actions recently introduced lightweight ubuntu-slim Runner as a cost-effective option (1 vCPU/5 GB RAM, maximum runtime of 15 minutes) ubuntu-latestHowever, manually identifying which workflows can be safely migrated is difficult and error-prone:

• ❌ Jobs that use Docker commands or containers cannot migrate
• ❌ use of jobs services: containers are incompatible
• ❌ Tasks longer than 15 minutes will fail
• ❌ Container-based GitHub Actions are not supported

gh-slimify Automates this entire processAnalyzing your workflow and securely transferring eligible jobs with a single command.

Install as GitHub CLI extension:

gh extension install fchimpan/gh-slimify

get help:

Scan a specific workflow file to find migration candidates:

gh slimify .github/workflows/ci.yml

Or scan multiple workflow files:

gh slimify .github/workflows/ci.yml .github/workflows/test.yml

To scan all workflows .github/workflows/Use --all flag:

Example output:

📄 .github/workflows/lint.yml
  ✅ Safe to migrate (1 job(s)):
     • "lint" (L8) - Last execution time: 4m
       .github/workflows/lint.yml:8
  ⚠️  Can migrate but requires attention (1 job(s)):
     • "build" (L15)
       ⚠️  Setup may be required (go), Last execution time: unknown
       .github/workflows/lint.yml:15
  ❌ Cannot migrate (2 job(s)):
     • "docker-build" (L25)
       ❌ uses Docker commands
       .github/workflows/lint.yml:25
     • "test-with-db" (L35)
       ❌ uses service containers
       .github/workflows/lint.yml:35

✅ 1 job(s) can be safely migrated
⚠️  1 job(s) can be migrated but require attention
❌ 2 job(s) cannot be migrated
📊 Total: 2 job(s) eligible for migration

The output shows:

• ✅ Safe to travel:Jobs with no missing commands and known execution time
• Migration may occur but requires attention:Jobs with missing commands or unknown execution time
• ❌ Cannot migrate: Jobs that cannot be migrated for specific reasons (for example, uses Docker commands, uses service containers, uses container syntax, does not run on Ubuntu-latest)
• due to warning: Displayed in one line for easy understanding
• relative file path: Clickable links that work in VS Code, iTerm2 and other terminal emulators

Automatically update eligible jobs for use ubuntu-slimBy default, only safe tasks (no missing commands and known execution time) are updated,

Specify the workflow file:

gh slimify fix .github/workflows/ci.yml

or use --all To fix all workflows:

Example output (default – only secure jobs):

Updating workflows to use ubuntu-slim (safe jobs only)...
Skipping 1 job(s) with warnings. Use --force to update them.

Updating .github/workflows/lint.yml
  ✓ Updated job "lint" (L8) → ubuntu-slim

Successfully updated 1 job(s) to use ubuntu-slim.

To update jobs with warnings (missing commands or unknown execution time), use this --force flag:

Example output (with –force):

Updating workflows to use ubuntu-slim (including jobs with warnings)...

Updating .github/workflows/lint.yml
  ⚠️  Updated job "build" (L15) → ubuntu-slim (with warnings)
  ✓ Updated job "lint" (L8) → ubuntu-slim

Successfully updated 2 job(s) to use ubuntu-slim.

To scan all workflows .github/workflows/Use --all flag:

you can also use --file (Or -f) Flag to specify workflow files:

gh slimify -f .github/workflows/ci.yml -f .github/workflows/test.yml

Skip getting task duration from GitHub API. It is useful for:

• API rate limit management: Avoid exceeding GitHub API rate limits when scanning multiple workflows
• fast scan:Skip API calls for quick results
• When API access is unavailable: Use when GitHub API is inaccessible

gh slimify --skip-duration

Use --verbose Flag to enable debug output, which can help troubleshoot problems with API calls or workflow parsing:

Update task with warnings (missing command or unknown execution time):

gh slimify fix .github/workflows/ci.yml --skip-duration --force
gh slimify --all --skip-duration
gh slimify fix --all --force

eligible for job migration ubuntu-slim If All The following conditions are met:

1. ✅ keeps going ubuntu-latest
2. ✅ does No Use docker command (docker build, docker run, docker composeetc.)
3. ✅ does No Use Docker-based GitHub Actions (for example, docker/build-push-action, docker/login-action,
4. ✅ does No Use services: Containers (PostgreSQL, Redis, MySQL, etc.)
5. ✅ does No Use container: Syntax (running jobs inside a Docker container)
6. ✅ Latest workflow run duration is less than 15 minutes (checked via GitHub API)
7. Jobs using existing orders ubuntu-latest but not inside ubuntu-slim (eg nvm) will be marked with warnings but they are still eligible for migration. You may need to add setup steps to install these tools ubuntu-slim,

Violation of any condition will result in loss of job No be transferred.

Jobs are classified into three categories:

• ✅ Safe to travel: No missing commands and execution time is not known
• Migration may occur but requires attention: There are missing commands or the execution time is unknown
• ❌ Cannot migrate: Does not meet the migration criteria (for example, uses Docker commands, uses service containers, uses container syntax, does not run on ubuntu-latest)

Missing orders are instruments that exist ubuntu-latest but it needs to be installed ubuntu-slim (As, nvmThese jobs can still be migrated, but you may need to add a setup step to install the required tools.

When a job cannot be transferred, specific reasons are displayed, such as:

• “does not run on ubuntu-latest”
• “uses docker command”
• “Uses container-based GitHub Actions”
• “Service uses containers”
• “uses container syntax”

jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
      - run: npm run lint

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: docker/build-push-action@v6
        with:
          context: .
          push: true

Result: ❌ Not eligible – uses Docker-based actions

jobs:
  test:
    runs-on: ubuntu-latest
    services:
      postgres:
        image: postgres:14
    steps:
      - run: npm test

Result: ❌ Not eligible – use services: containers

jobs:
  test:
    runs-on: ubuntu-latest
    container:
      image: node:18
    steps:
      - run: node --version

Result: ❌ Not eligible – use container: syntax

1. parse workflows:scan .github/workflows/*.yml Files and parse task definitions
2. check criteria: Evaluates each task against migration criteria (Docker, Services, Containers)
3. Find missing orders:Identifies commands used in jobs that exist ubuntu-latest but not inside ubuntu-slim
4. get period: Gets the latest task execution time from the GitHub API (unless --skip-duration Is used for)
5. Classify Jobs: Separates jobs into “safe” (no warnings), “requires attention” (warnings), and “cannot be moved” (does not meet the criteria) categories.
6. report results: Displays eligible jobs grouped by status:
   • Visual indicators (for safe, For warnings, ❌ for ineligible)
   • Ineligibility reasons for jobs that cannot be transferred
   • warning reason in one line
   • Relative file path with line numbers (clickable in most terminals)
   • execution period
7. auto fix (optional): update runs-on: ubuntu-latest To runs-on: ubuntu-slim,
   • By default: only safe jobs are updated
   • with --force: All eligible jobs (including warning jobs) are updated

mit license