Get GitHub git branch for AWS CodeBuild

Question

I'm setup AWS CodeBuild to build automatically from GitHub. Other CI services provide an environment variable for the branch, but I can't find one for AWS CodeBuild. There is a CODEBUILD_SOURCE_VERSION that is set to either pr/7 where 7 is the pull request number or the git commit sha.

Given the commit sha, I've been trying to get the branch name, but no luck so far.

git branch --contains <commitsha> doesn't work because it is a detached head. How do I get the git branch for the commit from CodeBuild?

Answer 1

You can get inspired by https://github.com/thii/aws-codebuild-extras

⚠️I don't recommend to run the curl command for security sake! If some vilain stole access to the thii/aws-codebuild-extras repo, you are screwed!

Just copy paste the script (understand it!) and add it to your docker image and then call it from your file system.

#!/bin/bash

export CI=true
export CODEBUILD=true

export CODEBUILD_GIT_BRANCH=`git symbolic-ref HEAD --short 2>/dev/null`
if [ "$CODEBUILD_GIT_BRANCH" == "" ] ; then
  CODEBUILD_GIT_BRANCH=`git branch -a --contains HEAD | sed -n 2p | awk '{ printf $1 }'`
  export CODEBUILD_GIT_BRANCH=${CODEBUILD_GIT_BRANCH#remotes/origin/}
fi

export CODEBUILD_GIT_MESSAGE=`git log -1 --pretty=%B`
export CODEBUILD_GIT_AUTHOR=`git log -1 --pretty=%an`
export CODEBUILD_GIT_AUTHOR_EMAIL=`git log -1 --pretty=%ae`
export CODEBUILD_GIT_COMMIT=`git log -1 --pretty=%H`
export CODEBUILD_GIT_TAG=`git describe --tags --abbrev=0`

export CODEBUILD_PULL_REQUEST=false
if [[ $CODEBUILD_GIT_BRANCH == pr-* ]] ; then
  export CODEBUILD_PULL_REQUEST=${CODEBUILD_GIT_BRANCH#pr-}
fi

export CODEBUILD_PROJECT=${CODEBUILD_BUILD_ID%:$CODEBUILD_LOG_PATH}
export CODEBUILD_BUILD_URL=https://$AWS_DEFAULT_REGION.console.aws.amazon.com/codebuild/home?region=$AWS_DEFAULT_REGION#/builds/$CODEBUILD_BUILD_ID/view/new

echo "==> AWS CodeBuild Extra Environment Variables:"
echo "==> CI = $CI"
echo "==> CODEBUILD = $CODEBUILD"
echo "==> CODEBUILD_GIT_AUTHOR = $CODEBUILD_GIT_AUTHOR"
echo "==> CODEBUILD_GIT_AUTHOR_EMAIL = $CODEBUILD_GIT_AUTHOR_EMAIL"
echo "==> CODEBUILD_GIT_BRANCH = $CODEBUILD_GIT_BRANCH "
echo "==> CODEBUILD_GIT_COMMIT = $CODEBUILD_GIT_COMMIT"
echo "==> CODEBUILD_GIT_MESSAGE = $CODEBUILD_GIT_MESSAGE"
echo "==> CODEBUILD_GIT_TAG = $CODEBUILD_GIT_TAG"
echo "==> CODEBUILD_PROJECT = $CODEBUILD_PROJECT"
echo "==> CODEBUILD_PULL_REQUEST = $CODEBUILD_PULL_REQUEST"

Answer 2

It's now possible to obtain this information directly from CodeBuild environmental variables:

• CODEBUILD_WEBHOOK_BASE_REF: The base reference name of the webhook event that triggers the current build. For a pull request, this is the branch reference.
• CODEBUILD_WEBHOOK_HEAD_REF: The head reference name of the webhook event that triggers the current build. It can be a branch reference or a tag reference.
• CODEBUILD_WEBHOOK_TRIGGER: Shows the webhook event that triggered the build. This variable is available only for builds triggered by a webhook. The value is parsed from the payload sent to CodeBuild by Github, Github Enterprise, or Bitbucket. The value's format depends on what type of event triggered the build.
  • For builds triggered by a pull request, it is pr/pull-request-number.
  • For builds triggered by creating a new branch or pushing a commit to a branch, it is branch/branch-name.
  • For builds triggered by a pushing a tag to a repository, it is tag/tag-name.

Answer 3

Add the following command to the install or pre_build phase of your buildspec.yml:

bash -c "$(curl -fsSL https://raw.githubusercontent.com/thii/aws-codebuild-extras/master/install)"

You can get more information about the build via the following environment variables: CI, CODEBUILD, CODEBUILD_GIT_AUTHOR, CODEBUILD_GIT_AUTHOR_EMAIL, CODEBUILD_GIT_BRANCH, CODEBUILD_GIT_COMMIT, CODEBUILD_GIT_MESSAGE, CODEBUILD_GIT_TAG, CODEBUILD_PROJECT, CODEBUILD_PULL_REQUEST.

Answer 4

You can run:

git branch -a --contains <sha>

-a means all branches. If your sha is in no branch, which could happen in some cases, you won't see anything.

Answer 5

CodeBuild strips git information from the filesystem. There is no .git folder, so running a git command will be fruitless.

I have added a parameter to my CI/CD CloudFormation template:

  GitBranch:
    Description: Github branch to be deployed
    Type: String
    Default: master

And I have a Bash script that creates / updates the CI/CD stack:

readonly git_branch=$(git branch 2>/dev/null | grep "^*" | colrm 1 2)

aws cloudformation create-stack \
  --stack-name ${cicd_stack_name} \
  --parameters ParameterKey=GitBranch,ParameterValue=${git_branch}

I then export the value as an environment variable to CodeBuild machine:

CodeBuildProject:
Type: AWS::CodeBuild::Project
Properties:
  Environment:
    Type: LINUX_CONTAINER
    Image: aws/codebuild/java:openjdk-8
    EnvironmentVariables:
      - Name: GIT_BRANCH
        Value: !Ref GitBranch

Now I have access to it in my buildspec.yml:

post_build:
  commands:
    - echo [PHASE] Entered the post_build phase...
    - echo "[DEBUG] Git branch ${GIT_BRANCH}"