September 18th, 2019
Tooling for Serverless
By Dustin Belliston

You have heard of serverless, no doubt. Many companies are starting to build serverless applications and explore the different use cases for them. The serverless future is exciting to say the least, and with more people joining the community we can see the reason for the buzz; it is fitting nicely into the world of cloud computing where we don’t want to fuss with managing infrastructure and want to focus on source code that differentiates our business.

This blog will walk you through some tooling setup for developing a serverless API. Once you have decided you want to start building a serverless API, this blog post will be handy. This is not an exhaustive tutorial but should get you moving in the right direction and help you navigate a few setup issues I had when starting.


In an ideal world you are given some requirements for your application. Let’s start there. Your design team has handed you some specs for a new web application they want for their machine learning team. One of the tasks they have assigned to you is to build an API that will allow a user to tag an image with classifications.


We are going to move past a few things that will need to be in place before you start with this. We are assuming you have an AWS environment and access to it, both through the web browser console and programmatic access set up with CLI.

Developer Tool 1: Build locally

A natural place to start building an API is with the AWS Lambda web console. When you navigate to the console, there is a simple wizard you can use to create a function. This is great and works for simple functions, but you will find that it will soon be less than adequate for working through building your API. You should choose a framework that will give you the ability to run and test Lambdas locally and then will aid you in packaging those and getting them to the Cloud. Google ‘Serverless Frameworks’ and you will see that there are many options. One provided by AWS is called AWS SAM. Let’s use that for this tutorial.

Install AWS SAM through the online docs.

Once installed, you can get a running serverless app with the ‘init’ command. This command will start you out with the following files:

sam init --runtime python3.7 
├── event.json 
├── hello_world 
│   ├── 
│   ├── 
│   └── requirements.txt 
├── template.yaml 
└── tests 
    └── unit 

This app is ready out of the box. You can start this locally with the command:

sam local start-api 

You can then invoke this function as it’s running through your browser at http://localhost:3000/hello.

Awesome! Lambdas running locally, starting out right. This will make it way easier to iterate over our code and get things in shape before deploying.

Developer Tool 2: Debug locally

I remember in my early days of web development console.log() was my best friend but, then I was taught how to use the Chrome debugger tool! Certainly, logging has a place, but a step through debugger is crucial to those super tricky situations where you wish you could pause time. Luckily, we can achieve that same developer experience with our serverless apps.

AWS SAM and VS Code play nice together. Let’s walk through setting up a debugging environment.

The AWS SAM docs are almost awesome. They got me pretty far, but a couple things were missing so they alone did not work for me. Start with the docs, which will help you set up ptvsd.

To set up ptvsd you will be walked through the pip install and then add a snippet of python code to the function that looks like this:

import ptvsd 
# Enable ptvsd on address and on port 5890 that we'll connect later with our IDE 
ptvsd.enable_attach(address=('', 5890), redirect_output=True) 
print('Hello, Im going to wait for vs code to attach to me before I continue...') 

With that in place, your code is ready, but VS Code now needs to be told how to work with the application. In the VS Code console, you should see the debug icon on the far-left pane, same location as where your file directory, search, extensions and git icon live. If you don’t see it, right click that pane and toggle the debug icon on. Click the debug and open the debug pane.

You will need to add a launch configuration to VS Code. This is a json definition that will tell VS Code where to find the running application and then where the source code will be. With the debug pane open, click on settings on the top left and add for python environment. There will be a few different configurations already in place. Just add the configuration below and make sure to add the correct localRoot. When you run the sam build command it generates the .aws-sam folder. The folder contains the bundles application and is the path you need to tell VS Code about. You will need to also tell it the function name inside the build folder.

  "name": "SAM CLI For Python Sample API", 
  "type": "python", 
  "request": "attach", 
  "port": 5890, 
  "host": "localhost", 
  "pathMappings": [ 
      "localRoot": "${workspaceFolder}/serverless-app-name/.aws-sam/build/NameOfFunction", 
      "remoteRoot": "/var/task" 

After that configuration is finished you can now run sam build to get any of the latest code changes. sam build takes your function source, gets all the dependencies then packages it inside the .aws-sam directory.

Run sam build.

Now your code is in the .aws-sam folder, review it to see how it is built, double check the launch configuration you have above has a valid localRoot path mapping

Run sam local start-api -d 5890.

This will start the API, listening on the default port 3000 with a debug port open at 5890. I wasn’t sure what this was doing at first, but basically that application is now available for the VS Code to latch onto at port 5890, which is the same port we defined in the debug launch configuration.

Go to browser and invoke the function http://localhost:3000/hello.

You can see in your terminal that the function stops. It is waiting at the point where our ptvsd code is waiting for attachment.

Now you can resume the debug with the debug feature in VS Code. Go to the top of the debug pane and select your launch configuration from the step above. This is where everything ties together. VS Code attaches to the debug port and takes you into the source code defined in the launch configuration.

Use the debug controls to navigate through the code.

Developer Tool 3: Package and deploy locally

The app is running locally. Super! AWS SAM makes the next step of deploying very easy. You will need to create an S3 bucket for the zipped artifact first.

aws s3 mb s3://mybucket-for-serverless

The following commands will package the Lambda function for us along with all its dependencies. AWS SAM is just CloudFormation with some syntactic sugar.

  • Build the app locally
    sam build
  • Package the template, code is placed in S3 and CloudFormation
    sam package \ 
      --output-template-file packaged.yaml \ 
      --s3-bucket BUCKET_NAME 
  • Deploy the app through CloudFormation stack
    sam deploy \ 
      --template-file packaged.yaml \ 
      --stack-name STACK_NAME \ 
      --capabilities CAPABILITY_IAM \ 
      --region us-east-1 

  • When you get more sophisticated there will be more that goes into building and deploying, but this is working great for us. SAM is going to package the Lambda for us, create an artifact, and setup that Lambda behind an API Gateway. Where did the API Gateway come in? Check out the template.yaml in the project folder and you can see that there are events tied to your function creation. The event type API is creating the API Gateway.

    Go to the console and check out what is created for Lambda, CloudFormation, and API Gateway. Make sure you are in the region set in your AWS CLI profile.

    In the output section of the CloudFormation stack you will see a URL for the API you have deployed.

    The URL will look something like

    Keep Going

    Hopefully this will give you some momentum with using AWS SAM for serverless development. I think it’s worthwhile to spend some time getting up to speed on serverless technologies and the tools available to help the developer experience be more enjoyable.

    If you have questions about AWS serverless technologies or any other AWS service, let us know! Schedule a consultation with our AWS Experts, or reach out to us at