Connecting a Lambda Function to AWS API Gateway

This is two part post. Please see part one.

• Part 1 Lambda Functions and DynamoDB

• Part 2 AWS API Gateway (This post.)

Setup the Lambda Function

In the last AWS post, we created a Lambda Function that could add an entry to a DynamoDB table.

This time we will connect that Lambda Function with API Gateway. For details on how to create a function, please see the previous post.

First, I’ll change the Lambda Function to accept incoming parameters in the event and use uniqid to create a new id for each new animal. This is what the Lambda Function we use will look like. (./animal.js will be the same as in my previous blog post.)

// index.js
const AnimalModel = require("./animal.js");
const uniqid = require("uniqid");

const handler = async (event) => {
  const animal = new AnimalModel({
    id: uniqid(),
    name: event.name,
    species: event.species
  })

  const resp = await animal.save();
  console.log(resp)
  const response = {
    statusCode: 200,
    body: JSON.stringify("Hello from " + resp.name + " the " + resp.species),
  };
  return response;
};

module.exports = { handler };

After making the changes, we will need to update our node_modules and upload a new zip file of our project to the cloud.

$ npm i uniqid

$ rm lambda.zip
$ zip -r lambda.zip . -x lamnda.zip
$ aws lambda update-function-code --function-name addToCityZoo --zip-file fileb://lambda.zip

Note that the Lambda Function takes a payload. Now we can test the function with a payload.

$ aws lambda invoke \
    --function-name addToCityZoo \
    --payload '{"name": "Gary", "species": "crocodile"}' \
    --invocation-type RequestResponse \
    --cli-binary-format raw-in-base64-out \
    /dev/stdout

The return value should look like this, and there should be a new entry in your DynamoDB table.

{"statusCode":200,"body":"\"Hello from Billy the crocodile\""}

Once this works, we can set up the API Gateway for our Lambda Function.

Setting up the API Gateway

We will go to the AWS Console to set up the API Gateway. I’ll show screenshots of how to do this.

Build a REST API

First, navigate to API Gateway and scroll down to find “Build REST API”

Build Rest API

Create API

Finish creating the REST API and name it.

Create API

Create a Resource

Create a resource. We will call it animals to hold animals for our zoo.

Use the Actions Menu Button to Create Resource.

Action Menu

Then finish creating the resource.

Create Resource

Method

To create a METHOD for the resource, click on the animals resource, then click on Actions again and select Create Method.

Create Method

Then select POST and click the checkmark so we can make a POST resource.

Create Method

Integrate the Lambda Function with the REST API.

We can select the action to be taken when the POST method is called in our REST function. Choose Lambda Function and type the name of our Lambda Function (which is addToCityZoo).

Integrate Lambda Function

Test the Lambda Function

Now we can test it from the console. Click on Test. Then…

Test integrated Lambda Function

Scroll down and add your POST data. We will use:

{"name": "Sam", "species": "bear"}

POST data for integrated Lambda Function

It should give you a result like:

{"statusCode":200,"body":"\"Hello from  Sam the bear\""}

Deploy the URI

Now go back the the Action menu button and click on Deploy. We can create a deploy called testing.

Deploy API

It will give you a deploy URI.

Deploy URI

Now you can access the lambda function from the Internet. We could use the URI from the above screen and curl to access the Lambda Function. Be sure to add our resource’s name animals to the URI. For example:

curl -X POST https://xxxxxxxxxx.execute-api.us-west-2.amazonaws.com/testing/animals -d '{"name": "Danny", "species": "bear"}'

And we will get this in response:

{"statusCode":200,"body":"\"Hello from Danny the bear\""}

So now we have a the Create/POST method of a REST API for animals

There is a GitHub repo to accompany this post here. For this post, take a look at the branch api-gateway.