Using GitLab CI/CD with a Bitbucket Cloud repository

GitLab CI/CD can be used with Bitbucket Cloud by creating a CI/CD project and connecting your Git repository via URL.

In GitLab create a CI/CD for external repo, select Repo by URL and create the project.

GitLab will import the repository and enable Pull Mirroring.
In GitLab create a Personal Access Token with api scope. This will be used to authenticate requests from the web hook that will be created in Bitbucket to notify GitLab of new commits.
In Bitbucket from Settings > Webhooks create a new web hook to notify GitLab of new commits.

The web hook URL should be set to the GitLab API to trigger pull mirroring, using the Personal Access Token we just generated for authentication.
```
https://gitlab.com/api/v4/projects/<NAMESPACE>%2F<PROJECT>/mirror/pull?private_token=<PERSONAL_ACCESS_TOKEN>
```
The web hook Trigger should be set to 'Repository Push'.

After saving, test the web hook by pushing a change to your Bitbucket repository.
In Bitbucket create an App Password from Bitbucket Settings > App Passwords to authenticate the build status script setting commit build statuses in Bitbucket. Repository write permissions are required.
In GitLab from Settings > CI/CD > Secret variables add variables to allow communication with Bitbucket via the Bitbucket API.

BITBUCKET_ACCESS_TOKEN: the Bitbucket app password created above

BITBUCKET_USERNAME: the username of the Bitbucket account

BITBUCKET_NAMESPACE: set this if your GitLab and Bitbucket namespaces differ

BITBUCKET_REPOSITORY: set this if your GitLab and Bitbucket project names differ

In Bitbucket add a script to push the pipeline status to Bitbucket.

Note: changes made in GitLab will be overwritten by any changes made upstream in Bitbucket.

Create a file build_status and insert the script below and run chmod +x build_status in your terminal to make the script executable.

#!/usr/bin/env bash

# Push GitLab CI/CD build status to Bitbucket Cloud

if [ -z "$BITBUCKET_ACCESS_TOKEN" ]; then
   echo "ERROR: BITBUCKET_ACCESS_TOKEN is not set"
exit 1
fi
if [ -z "$BITBUCKET_USERNAME" ]; then
    echo "ERROR: BITBUCKET_USERNAME is not set"
exit 1
fi
if [ -z "$BITBUCKET_NAMESPACE" ]; then
    echo "Setting BITBUCKET_NAMESPACE to $CI_PROJECT_NAMESPACE"
    BITBUCKET_NAMESPACE=$CI_PROJECT_NAMESPACE
fi
if [ -z "$BITBUCKET_REPOSITORY" ]; then
    echo "Setting BITBUCKET_REPOSITORY to $CI_PROJECT_NAME"
    BITBUCKET_REPOSITORY=$CI_PROJECT_NAME
fi

BITBUCKET_API_ROOT="https://api.bitbucket.org/2.0"
BITBUCKET_STATUS_API="$BITBUCKET_API_ROOT/repositories/$BITBUCKET_NAMESPACE/$BITBUCKET_REPOSITORY/commit/$CI_COMMIT_SHA/statuses/build"
BITBUCKET_KEY="ci/gitlab-ci/$CI_JOB_NAME"

case "$BUILD_STATUS" in
running)
   BITBUCKET_STATE="INPROGRESS"
   BITBUCKET_DESCRIPTION="The build is running!"
   ;;
passed)
   BITBUCKET_STATE="SUCCESSFUL"
   BITBUCKET_DESCRIPTION="The build passed!"
   ;;
failed)
   BITBUCKET_STATE="FAILED"
   BITBUCKET_DESCRIPTION="The build failed."
   ;;
esac

echo "Pushing status to $BITBUCKET_STATUS_API..."
curl --request POST $BITBUCKET_STATUS_API \
--user $BITBUCKET_USERNAME:$BITBUCKET_ACCESS_TOKEN \
--header "Content-Type:application/json" \
--silent \
--data "{ \"state\": \"$BITBUCKET_STATE\", \"key\": \"$BITBUCKET_KEY\", \"description\":
\"$BITBUCKET_DESCRIPTION\",\"url\": \"$CI_PROJECT_URL/-/jobs/$CI_JOB_ID\" }"

Still in Bitbucket, create a .gitlab-ci.yml file to use the script to push pipeline success and failures to Bitbucket.

stages:
  - test
  - ci_status

unit-tests
  script:
    - echo "Success. Add your tests!"

success:
  stage: ci_status
  before_script:
    - ""
  after_script:
    - ""
  script:
    - BUILD_STATUS=passed BUILD_KEY=push ./build_status
  when: on_success

failure:
  stage: ci_status
  before_script:
    - ""
  after_script:
    - ""
  script:
    - BUILD_STATUS=failed BUILD_KEY=push ./build_status
  when: on_failure

GitLab is now configured to mirror changes from Bitbucket, run CI/CD pipelines configured in .gitlab-ci.yml and push the status to Bitbucket.