CloudFormation Nested Stacks With Git Sync & a GitLab Pipeline Complete Overview

stages:
  - merge
  - deploy

merge_to_main:
  stage: merge
  image: alpine:latest
  before_script:
    - apk add --no-cache curl jq
  script:
    # Step 1: Check if an MR exists for the current branch
    - |
      echo "Checking if merge request exists for branch: $CI_COMMIT_REF_NAME"
      MR_INFO=$(curl --silent --header "PRIVATE-TOKEN: $GITLAB_API_TOKEN" \
        "$CI_API_V4_URL/projects/$CI_PROJECT_ID/merge_requests?source_branch=$CI_COMMIT_REF_NAME&state=all")
      MR_ID=$(echo "$MR_INFO" | jq -r '.[0].id')
      MR_STATE=$(echo "$MR_INFO" | jq -r '.[0].state')

      # Step 2: Create a new MR if the previous one is "merged" or "closed"
      if [ "$MR_ID" != "null" ] && { [ "$MR_STATE" = "merged" ] || [ "$MR_STATE" = "closed" ]; }; then
        echo "Existing merge request is $MR_STATE. Creating a new merge request..."
        MR_ID="null"
      fi

      if [ "$MR_ID" = "null" ]; then
        echo "No active merge request. Creating a new one..."
        response=$(curl --silent --request POST --header "PRIVATE-TOKEN: $GITLAB_API_TOKEN" \
          --data "source_branch=$CI_COMMIT_REF_NAME&target_branch=main&title=Merge branch $CI_COMMIT_REF_NAME&remove_source_branch=true" \
          "$CI_API_V4_URL/projects/$CI_PROJECT_ID/merge_requests")
        MR_ID=$(echo "$response" | jq -r '.id')
        if [ "$MR_ID" = "null" ]; then
          echo "Failed to create merge request for branch $CI_COMMIT_REF_NAME."
          echo "$response"
          exit 1
        fi
        echo "Created new merge request with ID: $MR_ID."
      else
        echo "Active merge request already exists with ID: $MR_ID."
      fi

    # Step 3: Automatically merge if the branch starts with aws-sync-
    - |
      if echo "$CI_COMMIT_REF_NAME" | grep -qE '^aws-sync-'; then
        echo "Branch starts with aws-sync-. Attempting automatic merge for MR $MR_ID..."
        merge_response=$(curl --silent --request PUT --header "PRIVATE-TOKEN: $GITLAB_API_TOKEN" \
          "$CI_API_V4_URL/projects/$CI_PROJECT_ID/merge_requests/$MR_ID/merge")

        if echo "$merge_response" | jq -e '.state == "merged"' > /dev/null; then
          echo "Merge request $MR_ID successfully merged."
        else
          echo "Failed to merge merge request $MR_ID."
          echo "$merge_response"
          exit 1
        fi
      else
        echo "Manual approval required for merge request $MR_ID."
      fi
  rules:
    - if: '$CI_COMMIT_REF_NAME == "main"'
      when: never  # Do not run on the main branch
    - when: always


upload_to_s3:
  stage: deploy
  image: registry.gitlab.com/gitlab-org/cloud-deploy/aws-base:latest
  script:
    - aws s3 sync . s3://ntwklab-cloudformation2 --exclude ".git/*" --delete
  environment: production
  rules:
    # Only run when the pipeline is for the main branch
    - if: $CI_COMMIT_REF_NAME == "main"
      when: always
    # Do not run for branches or unmerged code
    - if: '$CI_COMMIT_REF_NAME != "main"'
      when: never

template-file-path: vpc/deployment.yaml

AWSTemplateFormatVersion: '2010-09-09'
Resources:
  VPCStack:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: https://ntwklab-cloudformation2.s3.us-east-1.amazonaws.com/example/vpc.yaml

  Subnet1Stack:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: https://ntwklab-cloudformation2.s3.us-east-1.amazonaws.com/example/subnet1.yaml
      Parameters:
        VpcId: !GetAtt VPCStack.Outputs.VpcId

  Subnet2Stack:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: https://ntwklab-cloudformation2.s3.us-east-1.amazonaws.com/example/subnet2.yaml
      Parameters:
        VpcId: !GetAtt VPCStack.Outputs.VpcId

awscloudformation_addingnumbers % git status
On branch main
Your branch is up to date with 'origin/main'.
nothing to commit, working tree clean

awscloudformation_addingnumbers % git pull
Already up to date.

awscloudformation_addingnumbers % git checkout -b anewbranch
Switched to a new branch 'anewbranch'

awscloudformation_addingnumbers % git commit -am "a change to vpc-template" 
[anewbranch 251cf61] a change to vpc-template
 1 file changed, 2 deletions(-)

awscloudformation_addingnumbers % git push -u origin anewbranch
Enumerating objects: 7, done.
Counting objects: 100% (7/7), done.
Delta compression using up to 16 threads
Compressing objects: 100% (4/4), done.
Writing objects: 100% (4/4), 344 bytes | 344.00 KiB/s, done.
Total 4 (delta 3), reused 0 (delta 0), pack-reused 0
remote: 
remote: To create a merge request for anewbranch, visit:
remote:   https://gitlab.com/ntwklab1/awscloudformation_addingnumbers/-/merge_requests/new?merge_request%5Bsource_branch%5D=anewbranch
remote: 
To gitlab.com:ntwklab1/awscloudformation_addingnumbers.git
 * [new branch]      anewbranch -> anewbranch
branch 'anewbranch' set up to track 'origin/anewbranch'.