Configure images for flow execution

Flows that run with CI/CD execute inside a Docker image. By default, GitLab provides an image that includes the tools and network protection flows need. You can replace the default image with a custom or hardened image to add project dependencies, meet compliance requirements, or run flows in an offline environment.

Change the default Docker image

All flows executed with CI/CD use a Docker image provided by GitLab. This Docker image uses Anthropic Sandbox Runtime (srt) to automatically include network protection.

You can change the Docker image if you have a complex project with specific dependencies or tools.

To change the default Docker image, in the agent-config.yml file, add the following configuration:

image: YOUR_DOCKER_IMAGE

For example:

image: python:3.11-slim

image: node:20-alpine

Add network protection

To use network protection in your image, add srt to your Docker image with your preferred version:

# Install srt sandboxing with cache clearing and verification
ARG SANDBOX_RUNTIME_VERSION=0.0.20
RUN npm cache clean --force && \
    npm install -g @anthropic-ai/sandbox-runtime@${SANDBOX_RUNTIME_VERSION} && \
    test -s "$(npm root -g)/@anthropic-ai/sandbox-runtime/package.json" && \
    srt --version

For more information about SRT and how to install it on a custom image, see remote execution environment sandbox.

Use a custom image

If you use a custom Docker image, ensure that the following commands are available for the agent to function correctly:

• git
• npm with a Node.js version compatible with @gitlab/duo-cli. For more information, see GitLab Duo CLI prerequisites.

Most base images include these commands by default. However, minimal images (like alpine variants) might require you to install them explicitly. If needed, you can install missing commands in the setup script configuration.

Additionally, depending on the tool calls made by agents during flow execution, other common utilities might be required.

For example, if you use an Alpine-based image:

image: python:3.11-alpine
setup_script:
  - apk add --update git nodejs npm

Security and performance

When you use a custom Docker image, the environment sandbox is only applied when Anthropic Sandbox Runtime (SRT) is included in your custom image. If SRT is not included, your flow can access any domain reachable from the runner and the full file system.

If you require network isolation with custom images, install SRT on your image and configure a network policy, or configure network-level controls on your runner (for example, firewall rules or network policies).

To reduce job startup time by approximately 15-20 seconds, include the @gitlab/duo-cli npm package and the glab CLI in your custom image. The hardened image pre-installs both tools.

Use a custom image in an offline environment

In offline environments where runners cannot reach external registries, you can prebuild a custom executor image that includes @gitlab/duo-cli. When the GitLab Duo CLI is already in the image, the flow startup skips the npm download step.

Prerequisites:

• Administrator access.
• GitLab 18.9 or later.
• Access to an online machine to build the image and download artifacts.

To configure flows for an offline environment:

1. On an online machine, build a custom image with the GitLab Duo CLI:

   FROM registry.gitlab.com/gitlab-org/duo-workflow/default-docker-image/workflow-generic-image:v0.0.6
   RUN npm install -g @gitlab/duo-cli@8.86.0

   Alternatively, to avoid npm entirely, download the standalone binary from the GitLab package registry:

   FROM registry.gitlab.com/gitlab-org/duo-workflow/default-docker-image/workflow-generic-image:v0.0.6
   COPY duo-linux-x64 /usr/bin/duo
   RUN chmod +x /usr/bin/duo

   To download the standalone binary, run the following command:

   curl --location "https://gitlab.com/api/v4/projects/46519181/packages/generic/duo-cli/8.86.0/duo-linux-x64" \
     --output duo-linux-x64

2. Transfer the image to your offline environment. For example, with Docker, run the following commands:

   # On an online machine
   docker save my-duo-executor:latest -o duo-executor.tar
   
   # Transfer `duo-executor.tar` to the offline environment
   
   # On an offline machine
   docker load -i duo-executor.tar

3. Push the image to your internal container registry.

4. Set the custom image registry:

   1. In the upper-right corner, select Admin.
   2. In the left sidebar, select GitLab Duo.
   3. Select Change configuration.
   4. In the Image registry text box, enter your internal registry URL (for example, registry.internal.example.com).

5. In the top bar, select Search or go to and find your project.

6. To use the custom image, update the agent-config.yml file:

   image: registry.internal.example.com/duo-executor:latest

Use a Red Hat Universal Base Image 9 Minimal

GitLab provides a hardened, minimal image variant based on Red Hat Universal Base Image (UBI) 9 Minimal.

Use the hardened image when your environment requires:

• A Red Hat UBI base image. For example, for FedRAMP or enterprise compliance.
• Non-root container execution by default.
• A minimal attack surface with no language runtimes beyond what the Agent Platform itself needs.
• No outbound internet access at flow execution time (all Agent Platform dependencies are pre-installed)

The hardened image is published at registry.gitlab.com/gitlab-org/duo-workflow/default-docker-image/workflow-generic-image-hardened

It is built for both linux/amd64 and linux/arm64, and uses the following tag scheme:

• :<short-sha> for each build
• :<git-tag> for each release

Prerequisites:

• GitLab 18.10 or later

To use the hardened image, set it in your agent-config.yml:

image: registry.gitlab.com/gitlab-org/duo-workflow/default-docker-image/workflow-generic-image-hardened:<tag>

Image contents

The image includes @gitlab/duo-cli and glab. Outbound access to registry.npmjs.org or registry.gitlab.com is not needed at flow execution time.

Add additional packages

The hardened image runs as UID 1001 (duo-runner). The setup_script in your agent-config.yml also runs as this non-root user, so it cannot install system packages with microdnf.

To add language runtimes or system packages:

1. Extend the image with your own FROM layer:

   FROM registry.gitlab.com/gitlab-org/duo-workflow/default-docker-image/workflow-generic-image-hardened:<tag>
   
   USER root
   RUN microdnf install -y python3.12 python3.12-pip && microdnf clean all
   USER 1001

2. Use setup_script for project dependencies that do not require root access. For example, pip install --user or npm install.