CodeBuild: sam package computes a different MD5 hash for unchanged lambda source code

Description:

Setup i am having:

• a lambda function written in node.js
• sam template for that lambda
• buildspec that is running sam build and sam package
• everything is deployed via CodePipeline and is using CodeBuild
• code is deployed to github
• sam package that is running on the CodeBuild instance is computing a new MD5 hash for the lambda source code in spite of lambda function being changed or not
• i believe it has to do with the fact that CodeBuild environment is ephemeral, and the way we are calculating md5 hash here.

Code snippet:

@contextmanager
def zip_folder(folder_path):
    """
    Zip the entire folder and return a file to the zip. Use this inside
    a "with" statement to cleanup the zipfile after it is used.
    Parameters
    ----------
    folder_path : str
        The path of the folder to zip
    Yields
    ------
    zipfile_name : str
        Name of the zipfile
    md5hash : str
        The md5 hash of the directory
    """
    md5hash = dir_checksum(folder_path, followlinks=True)
    filename = os.path.join(tempfile.gettempdir(), "data-" + md5hash)

    zipfile_name = make_zip(filename, folder_path)
    try:
        yield zipfile_name, md5hash
    finally:
        if os.path.exists(zipfile_name):
            os.remove(zipfile_name)

Steps to reproduce:

• Create a simple lambda with sam
• create a buildspec that will run sam build + sam package
• Create CodePipeline with CodeBuild step
• Go to CodePipeline and run Release Change multiple time (essentially you are building the same revision)

Observed result:

• lambda is being redeployed each time you run release change in code pipeline

Expected result:

• this should not result in lambda being redeployed every time you run release change, since there were no code changes made

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

I will create a sample repo with the code shortly

[vijay2kr]

@mndeveci - The issue can be reproduced as follows in Code Pipeline:

1. Source stage - Github repo

2. Build stage: sam build sam package --output-template-file packaged.yaml --s3-bucket <S3 bucket>

3. Deploy stage: CloudFormationCreateUpdateStackAction

[Karthi96]

@mndeveci How are you deploying the stack in local env or via code pipeline? If you deploy via local then it works well but when you use code pipeline with code build and code deploy then the complete stack is redeploying without any modification. so the problem is md5 varies when deploying stack from the new environment.