---
stage: Verify
group: Pipeline Execution
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://handbook.gitlab.com/handbook/product/ux/technical-writing/#assignments
---

# Use kaniko to build Docker images **(FREE ALL)**

> [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/45512) in GitLab 11.2. Requires GitLab Runner 11.2 and above.

[kaniko](https://github.com/GoogleContainerTools/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](using_docker_build.md#use-docker-in-docker)
method:

- Docker-in-Docker requires [privileged mode](https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities)
  to function, which is a significant security concern.
- Docker-in-Docker generally incurs a performance penalty and can be quite slow.

## Prerequisites

To use kaniko with GitLab, [a runner](https://docs.gitlab.com/runner/) with one
of the following executors is required:

- [Kubernetes](https://docs.gitlab.com/runner/executors/kubernetes.html).
- [Docker](https://docs.gitlab.com/runner/executors/docker.html).
- [Docker Machine](https://docs.gitlab.com/runner/executors/docker_machine.html).

## 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 needs to be [overridden](using_docker_images.md#override-the-entrypoint-of-an-image),
  otherwise the build script doesn't run.

In the following example, kaniko is used to:

1. Build a Docker image.
1. Then push it to [GitLab container registry](../../user/packages/container_registry/index.md).

The job runs 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
[predefined CI/CD variables](../variables/index.md#predefined-cicd-variables)
GitLab CI/CD provides. These are automatically read by the Kaniko tool.

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:

```yaml
build:
  stage: build
  image:
    name: gcr.io/kaniko-project/executor:v1.14.0-debug
    entrypoint: [""]
  script:
    - /kaniko/executor
      --context "${CI_PROJECT_DIR}"
      --dockerfile "${CI_PROJECT_DIR}/Dockerfile"
      --destination "${CI_REGISTRY_IMAGE}:${CI_COMMIT_TAG}"
  rules:
    - if: $CI_COMMIT_TAG
```

If you authenticate against the [Dependency Proxy](../../user/packages/dependency_proxy/index.md#authenticate-within-cicd),
you must add the corresponding CI/CD variables for authentication to the `config.json` file:

```yaml
- echo "{\"auths\":{\"${CI_REGISTRY}\":{\"auth\":\"$(printf "%s:%s" "${CI_REGISTRY_USER}" "${CI_REGISTRY_PASSWORD}" | base64 | tr -d '\n')\"},\"$(echo -n $CI_DEPENDENCY_PROXY_SERVER | awk -F[:] '{print $1}')\":{\"auth\":\"$(printf "%s:%s" ${CI_DEPENDENCY_PROXY_USER} "${CI_DEPENDENCY_PROXY_PASSWORD}" | base64 | tr -d '\n')\"}}}" > /kaniko/.docker/config.json
```

This command strips the port, for example `:443`, from `CI_DEPENDENCY_PROXY_SERVER`, so you don't have to include it when referencing images.

### Building an image with kaniko behind a proxy

If you use a custom GitLab Runner behind an http(s) proxy, kaniko needs to be set
up accordingly. This means:

- Passing the `http_proxy` environment variables as build arguments so the Dockerfile
  instructions can use the proxy when building the image.

The previous example can be extended as follows:

```yaml
build:
  stage: build
  variables:
    http_proxy: <your-proxy>
    https_proxy: <your-proxy>
    no_proxy: <your-no-proxy>
  image:
    name: gcr.io/kaniko-project/executor:v1.14.0-debug
    entrypoint: [""]
  script:
    - /kaniko/executor
      --context "${CI_PROJECT_DIR}"
      --build-arg http_proxy=$http_proxy
      --build-arg https_proxy=$https_proxy
      --build-arg no_proxy=$no_proxy
      --dockerfile "${CI_PROJECT_DIR}/Dockerfile"
      --destination "${CI_REGISTRY_IMAGE}:${CI_COMMIT_TAG}"
  rules:
    - if: $CI_COMMIT_TAG
```

## Build a multi-arch image

You can build [multi-arch images](https://www.docker.com/blog/multi-arch-build-and-images-the-simple-way/)
inside a container by using [`manifest-tool`](https://github.com/estesp/manifest-tool).

For a detailed guide on how to build a multi-arch image, read [Building a multi-arch container image in unprivileged containers](https://blog.siemens.com/2022/07/building-a-multi-arch-container-image-in-unprivileged-containers/).

## 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:

```shell
$ /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:

```yaml
before_script:
  - |
    echo "-----BEGIN CERTIFICATE-----
    ...
    -----END CERTIFICATE-----" >> /kaniko/ssl/certs/ca-certificates.crt
```

## Video walkthrough of a working example

The [Least Privilege Container Builds with Kaniko on GitLab](https://www.youtube.com/watch?v=d96ybcELpFs)
video is a walkthrough of the [Kaniko Docker Build](https://gitlab.com/guided-explorations/containers/kaniko-docker-build)
Guided Exploration project pipeline. It was tested on:

- [GitLab.com shared runners](../runners/index.md)
- [The Kubernetes runner executor](https://docs.gitlab.com/runner/executors/kubernetes.html)

The example can be copied to your own group or instance for testing. More details
on what other GitLab CI patterns are demonstrated are available at the project page.

## Troubleshooting

### 403 error: "error checking push permissions"

If you receive this error, it might be due to an outside proxy. Setting the `http_proxy`
and `https_proxy` [environment variables](../../administration/packages/container_registry.md#running-the-docker-daemon-with-a-proxy)
can fix the problem.

### Error: `kaniko should only be run inside of a container, run with the --force flag if you are sure you want to continue`

There is a known incompatibility introduced by Docker Engine 20.10.

When the host uses Docker Engine 20.10 or newer, then the `gcr.io/kaniko-project/executor:debug` image in a version
older than v1.9.0 does not work as expected.

When you try to build the image, Kaniko fails with:

```plaintext
kaniko should only be run inside of a container, run with the --force flag if you are sure you want to continue
```

To resolve this issue, update the `gcr.io/kaniko-project/executor:debug` container to version at least v1.9.0,
for example `gcr.io/kaniko-project/executor:v1.14.0-debug`.

The opposite configuration (`gcr.io/kaniko-project/executor:v1.14.0-debug` image and Docker Engine
on the host in version 19.06.x or older) works without problems. For the best strategy, you should
frequently test and update job environment versions to the newest. This brings new features, improved
security and - for this specific case - makes the upgrade on underlying Docker Engine on the runner's
host transparent for the job.