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Build and Push to GHCR

This topic explains how to use the Build and Push an image to Docker Registry step to build and push an image to GitHub Container Registry.

You need:

Kubernetes cluster build infrastructures require root access​

With Kubernetes cluster build infrastructures, Build and Push steps use kaniko. Other build infrastructures use drone-docker. Kaniko requires root access to build the Docker image. It doesn't support non-root users.

If your build runs as non-root (runAsNonRoot: true), and you want to run the Build and Push step as root, you can set Run as User to 0 on the Build and Push step to use the root user for that individual step only.

If your security policy doesn't allow running as root, go to Build and push with non-root users.

Build and push to GitHub Container Registry​

In your pipeline's Build stage, add a Build and Push an image to Docker Registry step and configure the settings for GHCR.

Here is a YAML example of a Build and Push an image to Docker Registry step configured for GHCR:

- step:
    type: BuildAndPushDockerRegistry
    name: Build and push to GHCR
    identifier: Build_and_push_to_GHCR
    spec:
      connectorRef: YOUR_DOCKER_CONNECTOR_ID
      repo: ghcr.io/NAMESPACE/IMAGE
      tags:
        - <+pipeline.sequenceId>

When you run a pipeline, you can observe the step logs on the build details page. If the Build and Push step succeeds, you can find the uploaded image in GHCR.

tip

You can also:

Build and Push to Docker step settings for GHCR​

These sections explain how to configure the Build and Push an image to Docker Registry step settings for GHCR. Depending on the build infrastructure, some settings might be unavailable or optional. Settings specific to containers, such as Set Container Resources, are not applicable when using a VM or Harness Cloud build infrastructure.

Name​

Enter a name summarizing the step's purpose. Harness automatically assigns an Id (Entity Identifier) based on the Name. You can change the Id until the step is saved. Once save, the Id can't be changed.

Docker Connector​

Specify a Harness Docker Registry connector configured for GHCR.

To create this connector:

  1. Go to Connectors in your Harness project, organization, or account resources, and select New Connector.
  2. Select Docker Registry under Artifact Repositories.
  3. Enter a Name for the connector. The Description and Tags are optional.
  4. For Provider Type, Select Other.
  5. In Docker Registry URL, enter your GHCR hostname and namespace, such as https://ghcr.io/NAMESPACE. The namespace is the name of a GitHub personal account or organization.
  6. In the Authentication settings, you must use Username and Password authentication.
  7. Complete any other settings and save the connector. For information all Docker Registry connector settings, go to the Docker connector settings reference.

Docker Repository​

The namespace where you want to store the image and the image name, for example, ghcr.io/NAMESPACE/IMAGE_NAME. For more information, go to the GitHub documentation on Pushing container images.

Tags​

Add Docker build tags. This is equivalent to the -t flag. For more information, go to the GitHub documentation on Pushing container images.

Add each tag separately.

tip

When you push an image to a repo, you tag the image so you can identify it later. For example, in one pipeline stage, you push the image, and, in a later stage, you use the image name and tag to pull it and run integration tests on it.

Harness expressions are a useful way to define tags. For example, you can use the expression <+pipeline.sequenceId> as a tag. This expression represents the incremental build identifier, such as 9. By using a variable expression, rather than a fixed value, you don't have to use the same image name every time.

For example, if you use <+pipeline.sequenceId> as a tag, after the pipeline runs, you can see the Build Id in the output.

And you can see where the Build Id is used to tag your image in the container registry:

You can use the same expression to pull the tagged image, such as namespace/myimage:<+pipeline.sequenceId>.

Optimize​

With Kubernetes cluster build infrastructures, select this option to enable --snapshotMode=redo. This setting causes file metadata to be considered when creating snapshots, and it can reduce the time it takes to create snapshots. For more information, go to the kaniko documentation for the snapshotMode flag.

For information about setting other kaniko runtime flags, go to Environment variables.

Dockerfile​

The name of the Dockerfile. If you don't provide a name, Harness assumes that the Dockerfile is in the root folder of the codebase.

Context​

Enter a path to a directory containing files that make up the build's context. When the pipeline runs, the build process can refer to any files found in the context. For example, a Dockerfile can use a COPY instruction to reference a file in the context.

Kubernetes cluster build infrastructures

Kaniko, which is used by the Build and Push step with Kubernetes cluster build infrastructures, requires root access to build the Docker image. If you have not already enabled root access, you will receive the following error:

failed to create docker config file: open/kaniko/ .docker/config.json: permission denied

If your security policy doesn't allow running as root, go to Build and push with non-root users.

Labels​

Specify Docker object labels to add metadata to the Docker image.

Build Arguments​

The Docker build-time variables. This is equivalent to the --build-arg flag.

Target​

The Docker target build stage, equivalent to the --target flag, such as build-env.

Docker layer caching and Remote cache image​

There are two ways in which you can leverage Docker Layer Caching: Enable Docker layer caching ('caching' property) or Remote cache image ('remoteCacheRepo' property). Refer to Enable Docker layer caching for your build to learn more.

Environment Variables (plugin runtime flags)​

Build and Push steps use plugins to complete build and push operations. With Kubernetes cluster build infrastructures, these steps use kaniko, and, with other build infrastructures, these steps use drone-docker.

These plugins have a number of additional runtime flags that you might need for certain use cases. For information about the flags, go to the kaniko plugin documentation and the drone-docker plugin documentation.

How you configure plugin runtime flags depends on your build infrastructure.

Set plugin runtime flags with Kubernetes cluster build infrastructure

When using the built-in Build and Push steps with a Kubernetes cluster build infrastructure, you can use the Environment Variables setting to set kaniko plugin runtime flags.

warning

Unlike in other Harness CI steps, the Environment Variables setting in Build and Push steps only accepts the known kaniko plugin runtime flags. You must set other types of environment variables in your Dockerfile, build arguments, or as stage variables, depending on their usage and purpose in your build.

In Environment Variables, you must input a Name and Value for each variable. Format the name as PLUGIN_FLAG_NAME.

For example, to set --skip-tls-verify, add an environment variable named PLUGIN_SKIP_TLS_VERIFY and set the variable value to true.

              - step:
                  identifier: buildandpush
                  name: buildandpush
                  type: BuildAndPush---
                  spec:
                    ...
                    envVariables:
                      PLUGIN_SKIP_TLS_VERIFY: true

To build without pushing, use the no-push kaniko flag.

YAML example: Build and Push step with multiple environment variables

This YAML example shows a Build and Push to GAR step with several PLUGIN environment variables.

- step:
    identifier: pushGCR
    name: push GCR
    type: BuildAndPushGAR ## Type depends the selected Build and Push step, such as Docker, GAR, ACR, and so on.
    spec: ## Some parts of 'step.spec' vary by Build and Push step type (Docker, GAR, ACR, etc).
      connectorRef: GCR_CONNECTOR
      host: "us.gcr.io"
      projectID: "some-gcp-project"
      imageName: "some-image-name"
      tags:
        - "1.0"
        - "1.2"
      buildArgs:
        foo: bar
        hello: world
      labels:
        foo: bar
        hello: world
      target: dev-env
      context: "."
      dockerfile: "harnessDockerfile"
      remoteCacheImage: "test/cache"
      envVariables: ## Specify plugin runtime flags as environment variables under 'step.spec'.
        PLUGIN_TAR_PATH: ./harnesstarpath
        PLUGIN_IMAGE_DOWNLOAD_RETRY: "2"
        PLUGIN_COMPRESSED_CACHING: "false"
        PLUGIN_USE_NEW_RUN: "true"
        PLUGIN_GARBAGE: yoyo
Stage variables

Previously, you could set some kaniko runtime flags as stage variables. If you had done this and you are using Kubernetes cluster build infrastructure, then Harness recommends moving these kaniko plugin stage variables to the Environment Variables in your Build and Push step. Don't change non-kaniko plugin variables, such as PLUGIN_USER_ROLE_ARN.

For other types of environment variables (that aren't Build and Push plugin runtime flags), stage variables are still inherently available to steps as environment variables. However, where you declare environment variables depends on their usage and purpose in your build. You might need to set them in your Dockerfile, build args, or otherwise.

However some flags still require using a stage variable:

  • ignore-path: Set this flag to ignore a comma separated list of file paths when taking an image snapshot. Required when ignoring multiple paths.

Format these stage variables as PLUGIN_FLAG_NAME.

Set plugin runtime flags with other build infrastructures

With Harness Cloud, self-managed VM, or local runner build infrastructures, you can set some drone-docker plugin runtime flags as stage variable.

Currently, Harness supports the following drone-docker flags:

  • auto_tag: Enable auto-generated build tags.
  • auto_tag_suffix: Auto-generated build tag suffix.
  • custom_labels: Additional arbitrary key-value labels.
  • artifact_file: Harness uses this to show links to uploaded artifacts on the Artifacts tab.
  • dry_run: Disables pushing to the registry. Used to build without pushing.
  • custom_dns: Provide your custom CNS address.

To set these flags in your Build and Push steps, add stage variables formatted as PLUGIN_FLAG_NAME.

For example, to set custom_dns, add a stage variable named PLUGIN_CUSTOM_DNS and set the variable value to your custom DNS address.

variables:
  - name: PLUGIN_CUSTOM_DNS
    type: String
    description: ""
    required: false
    value: "vvv.xxx.yyy.zzz"
Mounting Docker Secrets

Harness now allows mounting Docker build secrets securely in 'Build and Push' steps. This feature enables you to pass sensitive data such as credentials or configuration files during Docker builds, either as environment variables or file-based secrets. It ensures secure handling of secrets, reducing the risk of exposing sensitive information.

note
  • This feature is currently configurable only through YAML.
  • In Kubernetes, unlike other build infrastructures (e.g., Harness Cloud), "Build and Push" steps default to Kaniko rather than Buildx. To enable this feature in Kubernetes, you must enable the feature flag CI_USE_BUILDX_ON_K8. Additionally, note that Kubernetes build infrastructure using Buildx requires privileged access.
YAML example: Mounting Docker secrets

This example demonstrates how to configure a Build and Push step with Docker secrets passed as both environment variables and file-based secrets:

- step:
    identifier: buildAndPush
    type: BuildAndPushDockerRegistry
    name: Build and Push Docker Image
    spec:
      connectorRef: dockerConnector
      repo: dockerRepo/imageName
      tags:
        - ci-<+pipeline.executionId>
      envDockerSecrets:
        a_user: USERNAME # Environment variable in format of key:value
        a_pass: PASSWORD
      fileDockerSecrets:
        docker_user2: <+secrets.getValue("myusername")> # File secret defined in Harness
        docker_pass2: <+secrets.getValue("mydockerpass")>
        docker_user3: /harness/test.txt # path to local file in workspace containing the secret
      caching: true

The envDockerSecrets field allows you to define environment variables to securely pass sensitive information to the Docker build process.

  • Key: The name of the environment variable that will be exposed to the Docker build process.
  • Value: The secret value associated with the key. This can either be a plain text string or a reference to a secret managed securely in Harness.

The fileDockerSecrets field allows you to mount secrets as files into the Docker build process. This is useful for passing configuration files, certificates, or other file-based sensitive data.

  • Key: The name of the secret as it will be referenced during the Docker build.
  • Value: The path to the file or a dynamic reference to a secret in Harness that will be mounted as a file.
Using Local Tar Output

In scenarios where pushing a Docker image to a registry is not feasible, you can generate a local tarball of the built image instead. This approach is particularly useful for situations like local testing or when registry access is unavailable during the build process.

Once the tarball is generated, you can use a Security Testing Orchestration (STO) step, such as Aqua Trivy, to scan the image for vulnerabilities. This workflow ensures that images are built and scanned effectively, even without access to a remote registry.

Here’s a sample partial pipeline that demonstrates how build the image, generate the tarball, and push it to the registry:

- step:
    type: BuildAndPushDockerRegistry
    name: BuildAndPushDockerRegistry_1
    identifier: BuildAndPushDockerRegistry_1
    spec:
      connectorRef: docker_connector
      repo: dockerhub/image_name
      tags:
        - linux-amd64
      caching: false
      dockerfile: ./docker/Dockerfile
      envVariables:
        PLUGIN_TAR_PATH: /harness/image_name.tar
- step:
    type: Run
    name: Run_2
    identifier: Run_2
    spec:
      shell: Sh
      command: ls /harness

The PLUGIN_NO_PUSH: "true" environment variable prevents the image from being pushed to the registry.Here’s a sample partial pipeline that demonstrates how build the image, generate the tarball, but skip pushing it to the registry:

- step:
    type: BuildAndPushDockerRegistry
    name: BuildAndPushDockerRegistry_1
    identifier: BuildAndPushDockerRegistry_1
    spec:
      connectorRef: docker_connector
      repo: dockerhub/image_name
      tags:
        - linux-amd64
      caching: false
      dockerfile: ./docker/Dockerfile
      envVariables:
        PLUGIN_TAR_PATH: /harness/image_name.tar
        PLUGIN_NO_PUSH: "true"
- step:
    type: Run
    name: Run_2
    identifier: Run_2
    spec:
      shell: Sh
      command: ls /harness
note

  • The local tar output feature is available only when using Kaniko as the build tool, which is commonly used in Kubernetes environments.

  • While the above examples show a push to a Docker registry, you can easily repurpose it for other registries by updating the step type, connector, and other relevant fields.

Run as User​

With Kubernetes cluster build infrastructures, you can specify the user ID to use to run all processes in the pod if running in containers. For more information, go to Set the security context for a pod.

This step requires root access. You can use the Run as User setting if your build runs as non-root (runAsNonRoot: true), and you can run the Build and Push step as root. To do this, set Run as User to 0 to use the root user for this individual step only.

If your security policy doesn't allow running as root, go to Build and push with non-root users.

Set Container Resources​

Set maximum resource limits for the resources used by the container at runtime:

  • Limit Memory: The maximum memory that the container can use. You can express memory as a plain integer or as a fixed-point number using the suffixes G or M. You can also use the power-of-two equivalents Gi and Mi. The default is 500Mi.
  • Limit CPU: The maximum number of cores that the container can use. CPU limits are measured in CPU units. Fractional requests are allowed; for example, you can specify one hundred millicpu as 0.1 or 100m. The default is 400m. For more information, go to Resource units in Kubernetes.

Timeout​

Set the timeout limit for the step. Once the timeout limit is reached, the step fails and pipeline execution continues. To set skip conditions or failure handling for steps, go to:

Conditions, looping, and failure strategies​

You can find the following settings on the Advanced tab in the step settings pane:

Troubleshoot Build and Push steps​

Go to the CI Knowledge Base for questions and issues related to building and pushing images, such as: