Transducers: Supercharge your functional JavaScript

This is the first in a series of posts on functional programming in JavaScript. My goal is to make these ideas more accessible to all levels of programmers. Feedback about style, content, etc., would all be greatly appreciated.

One thing that perplexed me early on in my functional programming days was the concept of transducers. I spent a lot of time Googling and found some great articles that went deep into the theory and the underlying mechanics. However, the practical use of them still seemed a bit out of reach. In this post I’ll attempt to explain transducers in a more understandable way and hopefully give you the confidence to use them in your functional JavaScript. While this article attempts to make transducers more accessible, you will need to have some basic knowledge of functional programming in JavaScript. Specifically, you should know about function composition and iterator functions like .map(), .filter(), and most importantly, .reduce(). If you are unfamiliar with these concepts, go get a grasp on them first.

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How To: Stub “.promise()” in AWS-SDK Node.js

Since AWS released support for Node v8.10 in Lambda, I was able to refactor Lambda API to use async/await instead of Bluebird promises. The code is not only much cleaner now, but I was able to remove a lot of unnecessary overhead as well. As part of the refactoring, I decided to use AWS-SDK’s native promise implementation by appending .promise() to the end of an S3 getObject call. This works perfectly in production and the code is super compact and simple:

The issue came with stubbing the call using Sinon.js. With the old promise method, I was using promisifyAll() to wrap new AWS.S3() and then stubbing the getObjectAsync method. If you’re not familiar with stubbing AWS services, read my post: How To: Stub AWS Services in Lambda Functions using Serverless, Sinon.JS and Promises.

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How To: Manage RDS Connections from AWS Lambda Serverless Functions

Someone asked a great question on my How To: Reuse Database Connections in AWS Lambda post about how to end the unused connections left over by expired Lambda functions:

I’m playing around with AWS lambda and connections to an RDS database and am finding that for the containers that are not reused the connection remains. I found before that sometimes the connections would just die eventually. I was wondering, is there some way to manage and/or end the connections without needing to wait for them to end on their own? The main issue I’m worried about is that these unused connections would remain for an excessive amount of time and prevent new connections that will actually be used from being made due to the limit on the number of connections.

🧟‍♂️ Zombie RDS connections leftover on container expiration can become a problem when you start to reach a high number of concurrent Lambda executions. My guess is that this is why AWS is launching Aurora Serverless, to deal with relational databases at scale. At the time of this writing it is still in preview mode.

Update September 2, 2018: I wrote an NPM module that manages MySQL connections for you in serverless environments. Check it out here.

Update August 9, 2018: Aurora Serverless is now Generally Available!

Overall, I’ve found that Lambda is pretty good about closing database connections when the container expires, but even if it does it reliably, it still doesn’t solve the MAX CONNECTIONS problem. Here are several strategies that I’ve used to deal with this issue.

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How To: Normalize URLs Stored in MySQL

I came across an interesting problem the other day. As part of our URL normalization strategy at AlertMe, we have been adding a trailing slash to URLs without file extensions. We did a lot of research when deciding on this tactic and the general consensus around the web was to use trailing slashes for directories and (obviously) no slashes on filenames. See this article from the official Google Webmasters blog: https://webmasters.googleblog.com/2010/04/to-slash-or-not-to-slash.html (I know it’s old, but the concept is still relevant).

We even tested a number of publisher URLs to see what their redirection strategies were. Every one we tested responded correctly to both the slash and no-slash versions of the URL. Some redirected to a trailing slash, some redirected to no trailing slash, but they all returned (or redirected to) the intended page.

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Is Code Really Self-Documenting?

In my 20+ years of programming, I’ve encountered a near endless amount of opinions on everything from coding styles to programming paradigms to the great whitespace debate. Obviously, I have strong opinions on a number of these. But for me, the one that bothers me the most is this notion that “code is self-documenting.” 😾

I know what you’re probably thinking: “of course not all code is self-documenting, only well-written code is.” I don’t entirely disagree. I can generally look at someone else’s code and understand exactly WHAT it is doing. However, often it’s not obvious WHY they did it that way, or even why they did it in the first place. In my opinion, the programmer’s intent (the WHY) is just as important as the HOW when it comes to properly documenting software.

So whether you agree with me or not, let’s explore how to better document our software by writing cleaner code, following some general commenting etiquette, and commenting more effectively to make you and your team more productive. 👍

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Securing Serverless: A Newbie’s Guide

So you’ve decided to build a serverless application. That’s awesome! May I be the first to welcome you to the future. 🤖 I bet you’ve done a lot of research. You’ve probably even deployed a few test functions to AWS Lambda or Google Cloud Functions and you’re ready to actually build something useful. You probably still have a bunch of unanswered questions, and that’s cool. We can still build some really great applications even if we only know the basics. However, when we start working with new things we typically make a bunch of dumb mistakes. While some are relatively innocuous, security mistakes can cause some serious damage.

I’ve been working with serverless applications since AWS launched Lambda in early 2015. Over the last few years I’ve developed many serverless applications covering a wide range of use cases. The most important thing I’ve learned: SECURE YOUR FUNCTIONS! I can tell you from personal experience, getting burned by an attack is no bueno. I’d hate to see it happen to you. 😢

To make sure it doesn’t happen to you, I’ve put together a list of 🔒Serverless Security Best Practices. This is not a comprehensive list, but it covers the things you ABSOLUTELY must do. I also give you some more things to think about as you continue on your serverless journey. 🚀

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How To: Build a Serverless API with Serverless, AWS Lambda and Lambda API

AWS Lambda and AWS API Gateway have made creating serverless APIs extremely easy. Developers can simply create Lambda functions, configure an API Gateway, and start responding to RESTful endpoint calls. While this all seems pretty straightforward on the surface, there are plenty of pitfalls that can make working with these services frustrating.

There are, for example, lots of confusing and conflicting configurations in API Gateway.  Managing deployments and resources can be tricky, especially when publishing to multiple stages (e.g. dev, staging, prod, etc.). Even structuring your application code and dependencies can be difficult to wrap your head around when working with multiple functions.

In this post I’m going to show you how to setup and deploy a serverless API using the Serverless framework and Lambda API, a lightweight web framework for your serverless applications using AWS Lambda and API Gateway. We’ll create some sample routes, handle CORS, and discuss managing authentication. Let’s get started.

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How To: Stub AWS Services in Lambda Functions using Serverless, Sinon.JS and Promises

I know the title is a quite a mouthful, but if you are trying to run tests on your Lambda functions that interact with AWS Services using the aws-sdk node module, then you’ve probably run into an issue stubbing or mocking the requests. In this post we’ll learn how to stub different AWS Services with Sinon.JS so that you can properly test your scripts.

UPDATE: AWS Lambda now supports Node v8.10, so we can use async/await instead of promises. The examples below still work with either v6.10 or v8.10, however, I recommend switching to async/await as they are more compact than promises. Read my post How To: Stub “.promise()” in AWS-SDK Node.js to learn how to deal with the .promise() method on aws-sdk services.

Let’s say you have a Lambda function that interacts with AWS’s SQS (Simple Queue Service). v6.10 of Node doesn’t support async/await, so you will most likely use promises if you don’t want to transpile your code or deal with callback hell. This means you need to Promisify an instance of the AWS SQS service. This is easy enough with:

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How To: Access Your AWS VPC-based Elasticsearch Cluster Locally

AWS recently announced that their Elasticsearch Service now supports VPC, which is awesome, for a number of reasons:

1. No more signing every request

Remember this?

Every request had to be signed with AWS’s SigV4 so that the Elasticsearch endpoint could be properly authorized. That meant additional code to sign all your requests, and additional time for the endpoint to decode it. It might only be a few milliseconds of extra processing time, but those can add up. Now we can call our VPC Elasticsearch endpoint with a simple HTTP request.

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Solve Your Own Problem…And You Have At Least One Customer

Last week I was deploying an app to AWS Lambda using Serverless and I accidentally misspelled a stage name. This resulted in deploying an entire CloudFormation stack with the wrong name, which wasted time and resources. I immediately realized that I spelled it wrong, so I was able to undeploy the stack quickly. I fully admit that misspelling the name was my fault, but since Serverless can deploy complex CloudFormation stacks that provision users, databases, SNS topics, etc., it seemed like there should be a better way to avoid this simple mistake.

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