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Over the last few weeks I have been working with a very ambitious client – Solve, who is building a new murder mystery game. They are doing some really cool things technically, and are building an entirely serverless stack.
While working with Solve I have spent a lot of time with AWS SAM. That experience also helped inform my opinion about SAM, as I explained in this article. Where compared with the Serverless framework it’s lacking the customizability that the serverless framework offers through its plugin system.
With the Serverless framework, I can write plugins to tailor the framework’s built-in behaviours. This gets me out of jail whenever I disagree with the framework’s choices. However, I don’t have such a luxury with SAM.
Just today, I ran into a problem with SAM’s support for AWS_IAM authorizer in API Gateway. The built-in behaviour is such that, anytime I choose to use AWS_IAM as the authorizer it’ll default the
CALLER_CREDENTIALS. Even if I explicitly set
This means the caller’s IAM role would be used to invoke the Lambda function. So, to call my IAM-protected endpoint, I need to sign the request with an IAM profile with the permissions to:
- execute-api:Invoke against the API Gateway resource
- and lambda:InvokeFunction against the Lambda function sitting behind API Gateway
That completely breaks the abstraction layer! As a caller, I not only need to know the endpoint I wish to talk to, but also how it’s implemented under the hood. If the API maintainer renames the functions behind the endpoint, my code would suddenly break.
If this issue also impacts you, then keep an eye on this Github issue.
Since SAM doesn’t have a plugin system, I would have to wait for the SAM team to fix the problem.
Or, do I?
Since SAM is ultimately just CloudFormation with a magical macro called
AWS::Serverless-2016–10–31. I can modify the CloudFormation template it transformed with my own macros.
In this case, we were able to get ourselves out of jail by writing a CloudFormation macro to:
- look for
- iteratively remove any
With this macro, we were able to unblock ourselves.
Admittedly, using CloudFormation macros is a rather heavy-handed approach to customize SAM’s behaviour! However, in the absence of a built-in mechanism for customizing SAM, it was the best bad idea we were able to come up with. Please let us know in the comments if you know of a simpler, more elegant solution!
p.s. Solve is looking for a backend engineer to join their team in Shoreditch, London. If you’re looking for an opportunity to work with serverless technologies and build games for millions of users, then you should consider applying!
I specialise in rapidly transitioning teams to serverless and building production-ready services on AWS.
Are you struggling with serverless or need guidance on best practices? Do you want someone to review your architecture and help you avoid costly mistakes down the line? Whatever the case, I’m here to help.
Check out my new podcast Real-World Serverless where I talk with engineers who are building amazing things with serverless technologies and discuss the real-world use cases and challenges they face. If you’re interested in what people are actually doing with serverless and what it’s really like to be working with serverless day-to-day, then this is the podcast for you.
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Here is a complete list of all my posts on serverless and AWS Lambda. In the meantime, here are a few of my most popular blog posts.
- Lambda optimization tip – enable HTTP keep-alive
- You are wrong about serverless and vendor lock-in
- You are thinking about serverless costs all wrong
- Just how expensive is the full AWS SDK?
- Many faced threats to Serverless security
- We can do better than percentile latencies
- Yubl’s road to Serverless
- AWS Lambda – should you have few monolithic functions or many single-purposed functions?
- AWS Lambda – compare coldstart time with different languages, memory and code sizes
- Guys, we’re doing pagination wrong
- Top 10 Serverless framework best practices