Do you know your Fan-Out/Fan-In from Map-Reduce?

Many students and clients have asked me how to implement Map-Reduce workloads serverlessly. In most cases, they are actually asking about Fan-Out/Fan-In!

At a glance, the two patterns look very similar and they are often used interchangeably in conversations. So in this post, let’s compare them and see how they differ.

CDK: how to customize 3rd-party L3 constructs

If you’re using CDK, you should use L3 constructs to encapsulate common patterns and best practices in your architecture.

However, sometimes you’d find a 3rd-party L3 construct that does most of what you want, but you need to customize how it configures some of its resources. That can be tricky because you don’t own the source code, and the construct author might not be willing to make the changes you want.

In this article, let me show you an easy and effective way to do this without having to clone and maintain a copy of the construct yourself.

How to handle execution timeouts in AWS Step Functions

Step Functions lets you set a timeout on both Task states and the whole execution. By default, an execution can run for a year if TimeoutSeconds is not configured. To a user, the execution would appear as “stuck”. Which is why AWS best practices recommend using timeouts to avoid such scenarios. But once you have configured a timeout for the execution, it’s then important to consider what happens when you experience a timeout.

In this post, let’s explore 3 ways you can handle an execution timeout and use a Lambda function to perform automated remediation (e.g. applying rollbacks).

How to apply the TDD mindset to serverless

Testing is an integral part of software development, and serverless is no different.

Test Driven Development, or TDD, is long regarded as a leading practice in software development. And yet, one of the most misunderstood parts of Test-Driven Development (TDD) is the “Driven” part of the name. It’s not just about “writing tests before you write the code”. If your tests do not inform and drive your API design, then you’re not really doing TDD.

In this post, let’s look at how we can apply the TDD mindset to serverless and use our tests to drive the design of our serverless application.

DynamoDB now supports cross-account access. But is that a good idea?

DynamoDB now supports resource-based policies, which simplified cross-account access to tables.

But just because you can, doesn’t mean you should!

Cross-account access to DynamoDB tables is almost always a smell. But as with everything, there are exceptions and edge cases. You should think carefully before you use resource-based policies to enable cross-account access to your DynamoDB tables.

In this post, let’s explore some legitimate use cases for cross-account access to DynamoDB tables.

When to use Step Functions vs. doing it all in a Lambda function

I’m a big fan of Step Functions, but it’s yet another AWS service you must learn and pay for.

It also introduces additional complexities. My application is harder to test; my business logic is split between configuration (ASL) and code; and I have new decision points, such as whether to use Express Workflows or Standard Workflows.

So it’s fair to ask, “Why should we even bother with Step Functions?”. Why not just do everything in code, inside a Lambda function?

Let’s break down the pros and cons and look at the trade-offs of each.

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