AWS Lambda functions that you can set to be triggered by Codecommit push triggers and it will trigger builds on any CodeBuild Project that has this repository as source.

lambda-codecommit-trigger-codebuild.py

import boto3

codecommit = boto3.client('codecommit')
codebuild  = boto3.client('codebuild')

def trigger_build(project, commit, branch):
    codebuild.start_build(projectName=project, sourceVersion=commit,
        environmentVariablesOverride=[
            { 'name': 'ENVIRONMENT', 'value': branch, 'type': 'PLAINTEXT' }
        ])

def handler(event, context):
    record = event['Records'][0]
    repo_name = record['eventSourceARN'].split(':')[5]
    repo = codecommit.get_repository(repositoryName=repo_name)
    repo_url = repo['repositoryMetadata']['cloneUrlHttp']

    paginator = codebuild.get_paginator('list_projects')
    page_iterator  = paginator.paginate()

    for page in page_iterator:

        projects = codebuild.batch_get_projects(names=page['projects'])
        for project in projects['projects']:

            src = project['source']
            if (src['type'] == 'CODECOMMIT' and src['location'] == repo_url):

                for ref in record['codecommit']['references']:

                    _, ref_type, ref_name = ref['ref'].split('/', 2)
                    if (ref_type == 'heads'):
                        branch = codecommit.get_branch(
                            repositoryName=project['name'], branchName=ref_name)
                        commit = branch['branch']['commitId']
                        trigger_build(project['name'], commit, ref_name)