I mean, who doesn't have code that they want to share between lambda functions?
And who doesn't want to debug those functions or business logic inside of those functions quickly--that doesn't require firing up the whole lambda into the AWS environment?
We wanted to have a utility package that wraps all of the details when accessing our architecture. We wanted the lambda functions to be as readable and minimal as possible.
I kid you not--it took three of us three to four days to figure out a reasonable solution!
Here were our requirements:
- Be able to debug locally
- Be able to run unit tests on business logic (without having to be ran in an AWS sandbox)
- Be able to run tests in sam local start-api
- Be able to debug the code in the container via sam local invoke
- sam build works
- sam deploy works
- Runs in AWS Lambda in the cloud
The first idea I had was to add a file reference to the package.json file inside the lambda folders and let npm pull those dependencies in. It worked perfectly--the first time. The second time I did a sam build, it DELETED all of the shared code! WHY? Apparently, when an .aws-sam folder exists, it performs an npm cleanup of some sort and that appears to delete the shared code. That was sad because that was a super clean implementation and I was reluctant to walk away from it.
Anyway, one of my coworkers went down another path and required dependencies using a ternary operator. If we're running in AWS, then require the full path where the layer is installed. Otherwise, require the relative path to the shared code.
We created a github repo to help others get an easy start, here: https://github.com/blmille1/aws-sam-layers-template.
I also created a stack overflow question and subsequently answered it here: https://stackoverflow.com/questions/60572458/how-do-i-use-shared-code-in-lambdas-in-an-aws-sam-template-using-layers-in-node/60572459#60572459
Please refer to them for a more in-depth explanation.
Be blessed!
