---
stage: Verify
group: Runner Core
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
title: Using LXD with the Custom executor
---

{{< details >}}

- Tier: Free, Premium, Ultimate
- Offering: GitLab.com, GitLab Self-Managed, GitLab Dedicated

{{< /details >}}

In this example, we use LXD to create a container per build and clean it
up afterwards.

This example uses a bash script for each stage. You can specify your
own image, which is exposed as
[CI_JOB_IMAGE](https://docs.gitlab.com/ci/variables/predefined_variables/).
This example uses the `ubuntu:22.04` image for simplicity. If you
want to support multiple images, you would have to modify the executor.

These scripts have the following prerequisites:

- [LXD](https://ubuntu.com/lxd)
- [GitLab Runner](../../install/linux-manually.md)

## Configuration

```toml
[[runners]]
  name = "lxd-driver"
  url = "https://gitlab.example.com"
  token = "xxxxxxxxxxx"
  executor = "custom"
  builds_dir = "/builds"
  cache_dir = "/cache"
  [runners.custom]
    prepare_exec = "/opt/lxd-driver/prepare.sh" # Path to a bash script to create lxd container and download dependencies.
    run_exec = "/opt/lxd-driver/run.sh" # Path to a bash script to run script inside the container.
    cleanup_exec = "/opt/lxd-driver/cleanup.sh" # Path to bash script to delete container.
```

## Base

Each stage [prepare](#prepare), [run](#run), and [cleanup](#cleanup)
will use this script to generate variables that are used throughout the
scripts.

It's important that this script is located in the same directory as the
other scripts, in this case `/opt/lxd-driver/`.

```shell
#!/usr/bin/env bash

# /opt/lxd-driver/base.sh

CONTAINER_ID="runner-$CUSTOM_ENV_CI_RUNNER_ID-project-$CUSTOM_ENV_CI_PROJECT_ID-concurrent-$CUSTOM_ENV_CI_CONCURRENT_PROJECT_ID-$CUSTOM_ENV_CI_JOB_ID"
```

## Prepare

The prepare script will do the following:

- Destroy a container with the same name if there is one running.
- Start a container and wait for it to start.
- Install [prerequisite dependencies](../custom.md#prerequisite-software-for-running-a-job).

```shell
#!/usr/bin/env bash

# /opt/lxd-driver/prepare.sh

currentDir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
source ${currentDir}/base.sh # Get variables from base.

set -eo pipefail

# trap any error, and mark it as a system failure.
trap "exit $SYSTEM_FAILURE_EXIT_CODE" ERR

start_container () {
    if lxc info "$CONTAINER_ID" >/dev/null 2>/dev/null ; then
        echo 'Found old container, deleting'
        lxc delete -f "$CONTAINER_ID"
    fi

    # The container image is hardcoded, but you can use
    # the `CI_JOB_IMAGE` predefined variable
    # https://docs.gitlab.com/ci/variables/predefined_variables/
    # which is available under `CUSTOM_ENV_CI_JOB_IMAGE` to allow the
    # user to specify the image. The rest of the script assumes that
    # you are running on an ubuntu image so modifications might be
    # required.
    lxc launch ubuntu:22.04 "$CONTAINER_ID"

    # Wait for container to start, we are using systemd to check this,
    # for the sake of brevity.
    for i in $(seq 1 10); do
        if lxc exec "$CONTAINER_ID" -- sh -c "systemctl isolate multi-user.target" >/dev/null 2>/dev/null; then
            break
        fi

        if [ "$i" == "10" ]; then
            echo 'Waited for 10 seconds to start container, exiting..'
            # Inform GitLab Runner that this is a system failure, so it
            # should be retried.
            exit "$SYSTEM_FAILURE_EXIT_CODE"
        fi

        sleep 1s
    done
}

install_dependencies () {
    # Install Git LFS, git comes pre installed with ubuntu image.
    lxc exec "$CONTAINER_ID" -- sh -c 'curl -s "https://packagecloud.io/install/repositories/github/git-lfs/script.deb.sh" | sudo bash'
    lxc exec "$CONTAINER_ID" -- sh -c "apt-get install -y git-lfs"

    # Install gitlab-runner binary since we need for cache/artifacts.
    lxc exec "$CONTAINER_ID" -- sh -c 'curl -L --output /usr/local/bin/gitlab-runner "https://gitlab-runner-downloads.s3.amazonaws.com/latest/binaries/gitlab-runner-linux-amd64"'
    lxc exec "$CONTAINER_ID" -- sh -c "chmod +x /usr/local/bin/gitlab-runner"
}

echo "Running in $CONTAINER_ID"

start_container

install_dependencies
```

## Run

This will run the script generated by GitLab Runner by sending
the content of the script to the container via `STDIN`.

```shell
#!/usr/bin/env bash

# /opt/lxd-driver/run.sh

currentDir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
source ${currentDir}/base.sh # Get variables from base.

lxc exec "$CONTAINER_ID" /bin/bash < "${1}"
if [ $? -ne 0 ]; then
    # Exit using the variable, to make the build as failure in GitLab
    # CI.
    exit $BUILD_FAILURE_EXIT_CODE
fi
```

## Cleanup

Destroy the container since the build has finished.

```shell
#!/usr/bin/env bash

# /opt/lxd-driver/cleanup.sh

currentDir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
source ${currentDir}/base.sh # Get variables from base.

echo "Deleting container $CONTAINER_ID"

lxc delete -f "$CONTAINER_ID"
```
