Optimizing Docker build performance

Building Docker images can be one of the most time-consuming parts of your CI/CD pipeline. Namespace runners accelerate your Docker builds through build distribution, layer caching, and integration with your existing workflows.

Quick start

No configuration changes required The fastest way to speed up your Docker builds is to simply switch to Namespace runners. Remote Builders are enabled by default and will immediately accelerate your builds.

jobs:
  build:
    runs-on: namespace-profile-default # was: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        # No docker/setup-buildx-action or docker/setup-qemu-action required!
      - name: Build and push
        uses: docker/build-push-action@v5
        with:
          context: .
          push: true
          tags: my-registry/my-app:latest

Note: If your workflow uses docker/setup-buildx-action, you need to remove or replace it. That’s it! Your builds are now running on high-performance Remote Builders with advanced caching.

Remote Builders

How Remote Builders transform your workflow

Remote Builders fundamentally change how Docker builds work in your CI/CD pipeline:

Scale independently: Massive parallel compute power regardless of your runner size
Cost optimization: Use smaller, cheaper runners while getting maximum build performance
Zero configuration: Every Docker command automatically benefits from remote acceleration
Universal compatibility: Works with docker build, docker/build-push-action, and any Docker-based tooling

Monitoring your accelerated builds

Every build launched from your runners appears in the interface providing direct access to detailed logs, timing metrics, and performance analytics.

This visibility helps you understand exactly how much time Remote Builders are saving. When looking at a slow build step, you can directly jump into the logs to understand which work was performed.

Head to Build Observability → to learn how to monitor build performance and identify bottlenecks.

Private registry (nscr.io)

Your builds get instant access to your private container registry at nscr.io with zero setup required. Authentication is handled automatically.

Push to your private registry

- name: Build and push to private registry
  uses: docker/build-push-action@v5
  with:
    context: .
    push: true
    tags: ${{ env.NSC_CONTAINER_REGISTRY }}/my-app:${{ github.sha }}

Pull from your private registry

- name: Use base image from private registry
  run: docker pull ${{ env.NSC_CONTAINER_REGISTRY }}/my-app:${{ github.sha }}

You can find a tag overview with history and usage statistics for pushed images in the dashboard.

Local caching

While Remote Builders provide the best performance for most scenarios, in-runner builders (locally cached) excel when building massive images (10GB+). Keeping the build local skips network transfer time. This section covers when to keep a build local. For caching container image pulls themselves, see Container Images. To enable this feature, just open the runner profile configuration and add a cache volume. Next, select Locally cached for your Docker builds. Make sure to size your cache appropriately to benefit from a high cache hit ratio.

locally cached Docker build configuration

Caveats

Build caching using “local caching” is not shared with Remote Builders; each repository uses its own separate cache.
Although multi-platform builds are supported, only builds of the same platform as the runner itself, will experience native performance.

Billing

Using local caching does not lead to any additional compute usage beyond the runner’s execution time itself. In order to make use of the feature, including logging and tracing, each build made with local caching counts towards the total build usage.

Optimize cache mounts

A common strategy to improve your build performance is the adoption of build cache mounts, allowing you to persist cache data across container builds and reduce build times significantly. With Namespace, your builds run in a shared, remote, high-performance builder by default, unlike on GitHub runners, where your docker builds run inside the runner. This sharing means that you’ll see more cache hits across different builds, and hence faster builds. Cache mounts allow multi-writer access by default. Some tools (e.g. apt) need exclusive access to its data. To achieve this, you can select sharing=locked which makes concurrent builds wait for another.

RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
    --mount=type=cache,target=/var/lib/apt,sharing=locked \
    apt update && apt-get --no-install-recommends install -y gcc

Builds without output

When you want to test a build without pushing or loading it, use the cacheonly output type. This runs the full build and populates the cache, but skips the export step:

- uses: docker/build-push-action@v6
  with:
    context: .
    outputs: type=cacheonly

Enterprise scaling

Need to run hundreds of concurrent builds? Namespace supports full-fanout builds that can handle enterprise-scale build volumes without performance degradation.

Automatic scaling: Remote Builders support automatic scale-out to match your build volume
No queue bottlenecks: Parallel processing ensures builds start immediately
Dedicated compute: With dedicated Namespace compute, you get a fully consistent build performance experience

Contact support@namespace.so to discuss custom scaling configurations for your build volume requirements.

Disable build caching

If you prefer to skip build caching altogether, you have two options:

Revert the Docker build context to the default: Namespace configures Remote Builders as a separate buildx context. Before invoking a build that should not be cached, you can switch back to the default by calling docker buildx use default. E.g.

jobs:
  build:
    steps:
      - name: Use default builder
        run: docker buildx use default

      - name: Build and push
        uses: docker/build-push-action@v5
        with:
          context: .
          platforms: linux/amd64,linux/arm64

Disable Remote Builders: You can request that runners created for a particular workflow job do not use Remote Builders. To disable Remote Builders, just open the runner profile configuration and select No caching for your Docker builds.

Migrating from GitHub Actions

Remove setup-buildx-action Because Namespace runners are configured out of the box to use Remote Builders, there is no need to set up or configure buildx separately. In fact, running docker/setup-buildx-action will overwrite the default configuration and prevent you from using Remote Builders. You can just remove docker/setup-buildx-action from your workflow entirely, or replace it with namespacelabs/nscloud-setup-buildx-action:

- name: Set up Docker Buildx
  uses: docker/setup-buildx-action@v3
  uses: namespacelabs/nscloud-setup-buildx-action@v0
- uses: docker/build-push-action@v5
  with:
    context: .

QEMU is not required

Multi-platform builds using Remote Builders don’t use emulation for AMD64 and ARM64 builds, instead building on these platforms natively. This results in much better performance for multi-platform builds, and also means there is no need to set up QEMU. When using Remote Builders, you can safely remove docker/setup-qemu-action, too:

steps:
  - uses: docker/setup-qemu-action@v3
  - uses: docker/setup-buildx-action@v3
  - uses: docker/build-push-action@v5
    with:
      context: .

Skip GitHub Actions caching

Traditional CI/CD requires complex caching strategies, but Namespace’s build infrastructure makes this unnecessary. Namespace build solutions include maximum layer caching out of the box. Using traditional GitHub Actions caching like cache-from/cache-to is superfluous when using Namespace builders and typically adds delays through remote file operations. You can remove them from your workflow definition:

- uses: docker/build-push-action@v5
  with:
    context: .
    cache-from: type=registry,ref=user/app:buildcache
    cache-to: type=registry,ref=user/app:buildcache,mode=max

What this means for you

No cache configuration: remove complex caching logic from your workflows.
Faster cold starts: even first builds benefit from shared layer caches.
Consistent performance: cache hit rates are optimized automatically.

Next steps

For advanced configuration see Runner Labels.

Products

Platform

Administration

Quick start

Remote Builders

How Remote Builders transform your workflow

Monitoring your accelerated builds

Private registry (nscr.io)

Push to your private registry

Pull from your private registry

Local caching

Caveats

Billing

Optimize cache mounts

Builds without output

Enterprise scaling

Disable build caching

Migrating from GitHub Actions

QEMU is not required

Skip GitHub Actions caching

What this means for you

Next steps

​Quick start

​Remote Builders

​How Remote Builders transform your workflow

​Monitoring your accelerated builds

​Private registry (nscr.io)

Push to your private registry

Pull from your private registry

​Local caching

​Caveats

​Billing

​Optimize cache mounts

​Builds without output

​Enterprise scaling

​Disable build caching

​Migrating from GitHub Actions

​QEMU is not required

​Skip GitHub Actions caching

​What this means for you

​Next steps

Quick start

Remote Builders

How Remote Builders transform your workflow

Monitoring your accelerated builds

Private registry (nscr.io)

Local caching

Caveats

Billing

Optimize cache mounts

Builds without output

Enterprise scaling

Disable build caching

Migrating from GitHub Actions

QEMU is not required

Skip GitHub Actions caching

What this means for you

Next steps