Sticky Disks

useblacksmith/stickydisk is a GitHub Action that helps persist state written to disk across jobs. This action can serve as a superior alternative to the Actions cache, especially when the cache artifacts are extremely large. Each sticky disk is hot-loaded into the runner and mounted at the specified path. The sticky disk is formatted as an ext4 filesystem.

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Cache Performance Comparison

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Use Cases

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NPM Package Caching

Node.js projects can have extensive dependency trees, leading to large node_modules directories. Sticky disks provide persistent, high-performance storage for your NPM packages.

jobs:
  build:
    runs-on: blacksmith
    steps:
      - uses: actions/checkout@v4
      
      - name: Setup Node.js
        uses: useblacksmith/setup-node@v5
        with:
          node-version: '18.x'
      
      - name: Mount NPM Cache
        uses: useblacksmith/stickydisk@v1
        with:
          key: ${{ github.repository }}-npm-cache
          path: ~/.npm
      
      - name: Mount node_modules
        uses: useblacksmith/stickydisk@v1
        with:
          key: ${{ github.repository }}-node-modules
          path: ./node_modules
      
      - name: Install Dependencies
        run: npm ci

      - name: Build
        run: npm run build

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Bazel Build Caching

Bazel’s remote cache can significantly improve build times, but uploading and downloading cached artifacts can still be a bottleneck. Using sticky disks with Blacksmith runners provides near-instant access to your Bazel caches as they are bind mounted into your runners on demand. Our useblacksmith/setup-bazel@v2 action is a zero-config way to use sticky disks to store the disk, repository, and external cache.

jobs:
  build:
    runs-on: blacksmith
    steps:
      - uses: actions/checkout@v4
      
      - name: Setup Bazel
        uses: useblacksmith/setup-bazel@v2
        with:
          version: '6.x'
      
      - name: Build
        run: |
          bazel build //...

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How it works

Blacksmith stores sticky disk artifacts in a secure, highly performant Ceph cluster, running on local NVMe drives. Our runners proxy their requests through our Storage Agents to interact with the Ceph cluster. Each sticky disk is uniquely identified by a key. When a GitHub Action job requests a sticky disk, the last committed snapshot will be cloned and mounted into the runner at the specified path. Once the job completes, the sticky disk will be unmounted and committed for future invocations. At the moment, customers can use up to 5 sticky disks in a single GitHub Action job.

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Using Sticky Disks inside a container

If your GitHub Actions job runs inside a container, you will need to ensure that the container is hydrated with certain Blacksmith specific environment variables and is running in privileged mode. These environment variables allow the runner to coordinate with our control plane to hotload and commit the sticky disks used in the workflow. The privileged mode is required for mounting and unmounting block devices inside a container.

The following changes can be made to your service container config in the workflow file:

   container:
      image: mcr.microsoft.com/playwright:v1.41.1
+     options: --privileged
+     env:
+       VM_ID: ${{ env.VM_ID }}
+       GITHUB_REPO_NAME: ${{ env.GITHUB_REPO_NAME }}
+       BLACKSMITH_STICKYDISK_TOKEN: ${{ env.BLACKSMITH_STICKYDISK_TOKEN }}
+       BLACKSMITH_INSTALLATION_MODEL_ID: ${{ env.BLACKSMITH_INSTALLATION_MODEL_ID }}
+       BLACKSMITH_REGION: ${{ env.BLACKSMITH_REGION }}

If the container image does not have sudo installed, you will need to install it as a step inside the container. sudo is required for mounting and formatting the sticky disk with proper permissions.

   steps:
      - name: Install sudo
        run: |
          apk add --no-cache sudo

Without these steps, you will see a 401 error, an Unauthenticated error, or permission-related errors when attempting to mount or use the sticky disk.

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Pricing

Sticky disks are billed at $0.50 per gigabyte per month, snapshotted by the hour.