Towards a Python version of my Javascript AWS CDK guide

After successfully using a Typescript CDK project to deploy a python lambda on Thursday, I decided to spend some time this evening creating a Python CDK guide. It's very limited at the moment (just a simple function and a basic lambda layer), but it's a start!

Enabling Programmable Bank Cards To Do All The Things

A little while back, Offerzen and Investec opened up their Programmable Bank Card Beta for South Africans, taking over from Root, and I was excited to be able to sign up!

My long-term goal with programmable banking is to integrate crypto transactions directly with my regular banking - which might be possible quite soon as Investec is starting to roll out its open API offering in addition to the card programme - and as far as I can tell that could be a real game-changer in terms of making crypto trading practical for non-investment purposes.

When I joined, though, what I found was a disparate group of really interesting projects and only a two-second time window to influence whether your card transaction will be approved or not.

I decided to bide my time by building a bridge for everyone else's solutions, one which would provide a central location to determine transaction approval and enable card holders (including myself, of course) to forward their transactions securely to as many services as they like without costing them running time on their card logic.

It was obvious to me that this needed to be a cloud solution, and as someone with zero serverless experience¹ I spent some time evaluating AWS, Google and Microsoft's offerings. My priorities were simple:

• right tool for the job
• low cost
• high performance
• good user experience

In the end AWS was the clear winner with the first two priorities, so much so that I didn't even bother worrying about any potential performance tradeoffs (there probably aren't any) and I was prepared to put up with their generally mixed bag of user experience. I also had the added incentive that my current employer uses AWS in their stack so I would be benefiting my employer at the same time.

Overall, I'm very glad that I chose AWS in spite of the trials and tribulations, which you can follow in my earlier post about building a template for CDK for beginners (like myself). In addition to learning how to use CDK, this project has given me solid experience in adapting to cloud architecture and patterns that are substantially different from anything I've worked with before, and I've already been able to effectively apply my learnings to my contract work.

One of the obligations of the Programmable Bank Card beta programme is sharing your work and presenting it; I was happy to do so, but for months I've been locked down and working in the same space as my wife and four year-old (we don't have room for an office or much privacy in our apartment); with all the distractions of home schooling and having to work while my wife and kid play my favourite video games I've barely been able to keep up my hours with my paid gig, so making time for extra stuff? That hasn't been so easy.

A couple of weeks ago my presentation was due, and I spent a lot of the preceding two weekends in a mad scramble to get my project as production-ready as I could - secure, reliable, usable. Half an hour before "go time" I finally deployed my offering, and I was a little bit nervous doing a live demo... I mean, sure, I'd tested all the end points after each deployment - but as we all know: Things Happen. Usually During Live Demos.

Fortunately, the presentation went very well! I spent the following weekend adding any missing "critical" functionality (such as scheduling lambda warmups and implementing external card usage updates), and I'm hoping that some of my fellow community members get some good use out of it (whether on their own stacks or mine).

The code can be found here on GitLab, and a few days ago OfferZen published the recording of my presentation on their blog along with its transcript² and my slide deck.

Thank you for joining me on my journey!

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¹ Although I was employed by one of the major cloud providers for a while, I've only worked "on" their cloud rather than "in", and while I do have extensive experience with Azure none of it included serverless functions.

² The transcript has a few minor transcription errors, but they're more amusing than confusing.

Resolving private PyPI configuration issues

The Story

I've spent the last few days wrestling with the serverless framework, growing fonder and fonder of AWS' CDK at every turn. I appreciate that serverless has been, until recently, very necessary and very useful, but I feel confident in suggesting that when deployment mechanisms become more complex than the code they're deploying things aren't moving in the right direction.

That said, this post is about overcoming what for us was the final hurdle: getting Docker able to connect to a private PyPI repository for our Python lambdas and lambda layers.

Python is great, kind of, but is marred by two rather severe complications: the split between python and python3, and pip… so it's a great language, with an awful tooling experience. Anyway, our Docker container couldn't communicate with our PyPI repo, it took way too long to figure out why, here's what we learned:

The Solution

If you want to use a private PyPI repository without typing in your credentials at every turn, there are two options:

1.

~/.pip/pip.conf:

2.

~/.pip/pip.conf:



~/.netrc:



It is important that ~/.netrc has the same owner:group as pip.conf, and that its permissions are 0600 (chmod 0600 ~/.netrc).

What's not obvious - or even discussed anywhere - is that special characters are problematic and are handled differently by the two mechanisms.

In pip.conf, the password MUST be URL encoded.
In .netrc, the password MUST NOT be URL encoded.

The Docker Exception

For whatever reason, solution 2 (the combination of pip.conf and .netrc) does NOT work with Docker.

Conclusion

Amazon's CDK is excellent, and unless you have a very specific use-case that it doesn't support it really is worth trying out!

Oh! And that Python is Very Nice, but simply isn't nice enough to justify the cost of its tooling.

A templated guide to AWS serverless development with CDK

If all you're looking for is a no-frills, quick, step-by-step guide, just scroll on down to The Guide!

The Story

Or, how I learned to let go of my laptop and embrace The Cloud...

Motivation

A while ago I outlined a project that I intend to build, one that I'm rather enthusiastic about, and after spending a few hours evaluating my options I decided that an AWS solution was the right way to go: their options are configurable and solid, their pricing is very reasonable and, as an added bonus, I get to familiarize myself with tech I'll be using for my current contract!

All good.

Once I'd made the decision to use AWS, becoming generally familiar with the products on offer was easy enough and it took me very little time to flesh out a design. I was ready to get coding!

Or so I thought...

Hurdle 1

Serverless. And possibly other frameworks, I'm pretty sure I looked at a few but it seems like forever ago. Serverless shows lots of promise, and I know people who swear by it, but it's only free up to a point and I immediately ran into strange issues with my first deployment. I found the interface surprisingly unhelpful, and it looks like once you're using it you're somewhat locked in.

Pass.

Hurdle 2

Cognito. Security first. Cognito sounds like a great solution, but once I'd gotten a handle on how it works I was severely disappointed by how limiting it is, and getting everything set up takes real developer and user effort (and I suffer enough from poor interface fatigue). After playing around with user pools and looking at various code samples, I realized that I'd rather allow users to register using their email addresses / phone numbers as 2nd-factor authentication (mailgun and twilio are both straightforward options), or use oauth providers like Facebook, Google and GitHub, and I certainly want to encourage my users to use strong, memorable passwords (easily enforced with zxcvbn, and why is this still a thing?!) which Cognito doesn't allow for.

You'll need to configure Lambda authorizers either way, so I really don't think Cognito adds much value.

Hurdle 3

Lambda / DynamoDB. Okay, so writing a lambda function is really easy, and guides and examples for code that reads to and writes from DynamoDB abound. Great! Except for the part where you need to test your functions before deploying them.

My first big mistake - and so far it's proved to be the most expensive one - was not understanding at this point that "testing locally" is simply not a feasible strategy for a cloud solution.

Hurdle 4

The first code I wrote for my project was effectively a lambda environment emulator to test my lambda functions. It was far from perfect, and it did take me a couple of hours to cobble together, but it did the job and I used it to successfully test lambda functions against DynamoDB running in Docker.

Hurdle 5

Lambda Layers. Why do most guides not touch on these? Why are there so few layers guides written for Javascript? It took me a little while to get a handle on layers and build a simple script to create them from package.json files, but as far as hurdles go this was a relatively short one.

Hurdle 6

Deployment. It's nice to have code running locally, but uploading it to the cloud? Configuring API Gateway was a mixed bag of Good Interface / Bad Interface, same with the Lambda functions, and what eventually stumped me was setting up IAM to make everything play nicely together. What's the opposite of intuitive? Not counter-intuitive, in this case, as I don't feel that that word evokes nearly enough frustration.

Anyway, it became abundantly clear at that point that manual deployment of AWS configurations and components is not a viable strategy.

Hurdle 7

A coworker introduced me to two tools that could supposedly Solve All My Problems: CDK and SAM. This seemed like a worthy rabbit-hole to crawl into, but I couldn't find any examples of the two working together!

I began to build my own little framework, one that would allow me to configure my stack using CDK, synthesize the CloudFormation templates, and test locally using SAM. Piece by piece I put together this wonderful little tool, hour by hour, first handling DynamoDB, then Lambda functions, then Lambda Layers...

It was at that point that realization dawned: not only are SAM and CDK not interoperable by design, but SAM does not, in fact, provide meaningful "local" testing. Sure, you can invoke your lambda functions on your local machine, but the intention is to invoke them against your deployed cloud infrastructure. Once I got that through my head, it was revelation time: testing in the cloud is cheaper and better than testing locally.

The Guide

If you're like me, and you intend your first foray into cloud computing to be simple, yet reasonably production-ready, CDK is the easiest way forward and it's completely free (assuming you don't factor in your time figuring it out as valuable, but that's what I'm here for!).

Over the course of the past couple of weeks, I've put together the aws-cdk-js-dev-guide. It's a work in progress (next stop, lambda authenticators!), but at the time of writing this guide it's functional enough to put together a simple stack that includes Lambda Layers, DynamoDB, functions using both of those, API Gateway routes to those functions and the IAM permissions that bind them.

And that's just the tip of the CDK iceberg.

Step 1 - Tooling

It is both valuable and necessary to go through the following steps prior to creating your first CDK project:

• Create a programmatic user in IAM with admin permissions
• If you're using Visual Studio Code (recommended), configure the aws toolkit
• Set up credentials with the profile ID "default"
• Get your 12 digit account ID from My Account in the AWS console
• Follow the CDK hello world tutorial

Step 2 - Creating a new CDK project

The first step to creating a CDK project is initializing it with cdk init, and a CDK project cannot be initialized if the project directory isn't empty. If you would like to use an existing project (like aws-cdk-js-dev-guide) as a template, bear in mind that you will have to rename the stack in multiple locations and it would probably be safer and easier to create a new project from scratch and copy and paste in whatever bits you need.

Step 3 - Stack Definition

There are many viable approaches to setting up stages, mine is to replicate my entire stack for development, testing and production. If my stack wasn't entirely serverless - if it included EC2 or Fargate instances, for example - then this approach might not be feasible from a cost point of view.

Stack definitions are located in the /lib folder, and this is where the stacks and all their component relationships are configured. Here you define your stacks programmatically, creating components and connecting them.



I find that the /lib folder is a good place to put your region configurations.



Once you have completed this, the code to synthesize the stack(s) is located in the /bin folder. If you intend, like I do, to deploy multiple replications of your stack, this is the place to configure that.



See the AWS CDK API documentation for reference.

Step 4 - Lambda Layers

I've got much more to learn about layers at the time of writing, but my present needs are simple: the ability to make npm packages available to my lambda functions. CDK's Code.fromAsset method requires the original folder (as opposed to an archive file, which is apparently an option), and that folder needs to have the following internal structure:

.
.nodejs
.nodejs/package.json
.nodejs/node_modules/*

You can manually create this folder anywhere in your project, maintain the package.json file and remember to run npm install and npm prune every time you update it... or you can just copy in the build-layers script, maintain a package.json file in the layers/src/my-layer-name directory and run the script as part of your build process.

Step 5 - Lambda Functions

There are a number of ways to construct lambda functions, I prefer to write mine as promises. There are two important things to note when putting together your lambda functions:

1. Error handling: if you don't handle your errors, lambda will handle them for you... and not gracefully. If you do want to implement your lambda functions as promises, as I have, try to use "resolve" to return your errors.

2. Response format: your response object MUST be in the following structure:

This example lambda demonstrates using a promise to return both success and failure responses:

Step 6 - Deployment

There are three steps to deploying and redeploying your stacks:

1. Build your project
   If you're using Typescript, run
   > tsc
   If you're using layers, run the build-layers script (or perform the manual steps)
   
2. Synthesize your project
   > cdk synth
   
3. Deploy your stacks
   > cdk deploy stack-name
   Note: you can deploy multiple stacks simultaneously using wildcards

At the end of deployment, you will be presented with your endpoints. Unless your lambda has its own routing configured - see the sample dynamodb API examples that follow - simply make your HTTP requests to those URLs as is.

Sample dynamodb API call examples:
• List objects
  GET https://xxxxxxxxxx.execute-api.us-east-1.amazonaws.com/prod/objects
• Get specific object
  GET https://xxxxxxxxxx.execute-api.us-east-1.amazonaws.com/prod/objects/b4e01973-053c-459d-9bc1-48eeaa37486e
• Create a new object
  POST https://xxxxxxxxxx.execute-api.us-east-1.amazonaws.com/prod/objects
• Update an existing object
  POST https://xxxxxxxxxx.execute-api.us-east-1.amazonaws.com/prod/objects/b4e01973-053c-459d-9bc1-48eeaa37486e

Step 7 - Debugging

Error reports from the API Gateway tend to hide useful details. If a function is not behaving correctly or is failing, go to your CloudWatch dashboard and find the log group for the function.

Step 8 - Profit!!!

I hope you've gotten good use of this guide! If you have any comments, questions or criticism, please leave them in the comments section or create issues at https://github.com/therightstuff/aws-cdk-js-dev-guide.