• Requirements
• Building a Docker image with kaniko
• Using a registry with a custom certificate

Building images with kaniko and GitLab CI/CD

kaniko is a tool to build container images from a Dockerfile, inside a container or Kubernetes cluster.

kaniko solves two problems with using the docker-in-docker build method:

• Docker-in-docker requires privileged mode in order to function, which is a significant security concern.
• Docker-in-docker generally incurs a performance penalty and can be quite slow.

Requirements

In order to utilize kaniko with GitLab, a GitLab Runner using one of the following executors is required:

• Kubernetes.
• Docker.
• Docker Machine.

Building a Docker image with kaniko

When building an image with kaniko and GitLab CI/CD, you should be aware of a few important details:

• The kaniko debug image is recommended (gcr.io/kaniko-project/executor:debug) because it has a shell, and a shell is required for an image to be used with GitLab CI/CD.
• The entrypoint will need to be overridden, otherwise the build script will not run.
• A Docker config.json file needs to be created with the authentication information for the desired container registry.

In the following example, kaniko is used to:

1. Build a Docker image.
2. Then push it to GitLab Container Registry.

The job will run only when a tag is pushed. A config.json file is created under /kaniko/.docker with the needed GitLab Container Registry credentials taken from the environment variables GitLab CI/CD provides.

In the last step, kaniko uses the Dockerfile under the root directory of the project, builds the Docker image and pushes it to the project’s Container Registry while tagging it with the Git tag:

build:
  stage: build
  image:
    name: gcr.io/kaniko-project/executor:debug
    entrypoint: [""]
  script:
    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
    - /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
  only:
    - tags

Using a registry with a custom certificate

When trying to push to a Docker registry that uses a certificate that is signed by a custom CA, you might get the following error:

$ /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --no-push
INFO[0000] Downloading base image registry.gitlab.example.com/group/docker-image
error building image: getting stage builder for stage 0: Get https://registry.gitlab.example.com/v2/: x509: certificate signed by unknown authority

This can be solved by adding your CA’s certificate to the kaniko certificate store:

  before_script:
    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
    - |
      echo "-----BEGIN CERTIFICATE-----
      ...
      -----END CERTIFICATE-----" >> /kaniko/ssl/certs/ca-certificates.crt