If you've been following this series, you know what AWS Lambda Managed Instances (LMI) are and what they cost. In Part 1 we covered the overview and in Part 2 we dug into the cost model. Now it's time to answer the question that actually matters for day-to-day development: will my existing Lambda code work on LMI, and what will I need to change?

The short answer is: maybe - and possibly quite a bit.

The execution model is fundamentally different from on-demand Lambda. Don't assume your code will behave the same way - some of these differences will silently corrupt your data, and others will just make your life harder. Read through all of them before migrating anything to production.

You've likely seen the AWS launch post and are intrigued by what AWS Lambda Managed Instances (AWS LMI) can offer. You may have even read my overview of AWS LMI in an earlier blog post.

In this post, we'll look at AWS Lambda On-Demand costs, how costs change with AWS LMI, when it makes sense to use AWS LMI and when it makes sense to stick with On-Demand AWS Lambda.

You've optimized your Lambda functions six ways from Sunday, but costs are still eating your budget. AWS LMI might help.

You've bought in to using containers to package AWS Lambda functions but now you're curious...

If you had to, could you migrate that same function to AWS Fargate?

You're a Docker pro - or maybe you just work somewhere with strong opinions about how containers should be built. Either way, let's talk about bringing your own container images to AWS Lambda.

You're a Go (or Rust) developer and you're really looking forward to deploying your awesome Lambda application in a OS-only container. Let's look at how to do it.

Your Lambda function just hit the 250MB unzipped size limit.

Again.

You're wrestling with Layers and code dependencies, wondering if there's a better way.

There is — and it might surprise you how simple container packaging makes this problem disappear.

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