Sanket Patel

Posted on May 21, 2019 • Updated on May 31, 2019

How To Create Serverless API Functions With AWS Lambda

#serverless #aws #node #javascript

In this tutorial, we will learn how to create the serverless API functions. We will be using the serverless framework and host the functions to AWS Lambda.

Wondering why serverless?

Please check AWS Lambda or Cloudflare's why use serverless.

Get started

Install the serverless globally

npm install -g serverless

Check if it is installed by running serverless -v command on terminal

serverless -v
1.42.3

Get the boilerplate

We will use the aws-nodejs template to create our service, let say with the name testing-one.

sls create --template aws-nodejs --path testing-one

Where sls is a shortcut of serverless.

The default template will have handler.js. It contains a dummy function called hello. The business logic should go inside it. In the next step, we will deploy the same function to AWS Lambda.

Let's simplify the hello function and return the message as below:

module.exports.hello = async event => {
  return {
    statusCode: 200,
    body: JSON.stringify(
      {
        message: `Hi, there!`
      },
      null,
      2
    )
  };
};

Deploy to AWS Lambda

For deploying the functions to AWS, we need to set up credentials in our machine.

If it is already set up in your machine, the below command should display the access key id and secret access key

cat < ~/.aws/credentials

[default]
aws_access_key_id = your-access-key-id
aws_secret_access_key = your-secret-access-key

Else, please follow this video, to set up the AWS credentials.

To deploy the function, run the deploy command

sls deploy

If you navigate to the AWS Lambda console (https://console.aws.amazon.com > Services > Lambda > Function), you will find the hello function deployed there. (Make sure you have selected the correct region at top-right of the screen)

The function name testing-one-dev-hello displayed is in the following format.

< service name > - < stage > - < function name >

Invoke deployed function

sls invoke -f hello

{
 "statusCode": 200,
 "body": "{\n  \"message\": \"Hi, there!\"\n}"
}

where -f is shorthand of -function.

So the function hello is deployed and running. Let's make it a REST API function.

Use the function as REST API

Events are the things that trigger your functions to run. One of such kind of event is HTTP event. The HTTP event can be generated by one of the HTTP endpoints.

Creating GET endpoint

Let say we want to trigger the hello function when a GET HTTP request made to the path /hello.

That is, GET : https://someurl.com/hello

The file serverless.yml is exactly for such kind of configuration in the serverless project.

YAML (.yml) is a data-serialization language and used for configuration files. It's just like JSON but more human readable friendly.

In serverless.yml, change the functions sections as shown below.

Please ensure you have proper indentation as per YAML standards. You can also learn by playing at http://nodeca.github.io/js-yaml/

functions:
  hello:
    handler: handler.hello
    events:
      - http:
          path: hello
          method: get

Deploy the changes

sls deploy

The deploy command output should return you the URL endpoints that we should use to trigger the function.

You can browse the endpoint in the browser. It will hit the lambda function and will return the below result.

{
  "message": "Hi, there!"
}

Accept Query String parameters

You can also pass the query string parameters and process it in your business logic.

Let's update the hello function to process the name parameter passed in as query string

module.exports.hello = async event => {
  if (event.queryStringParameters && event.queryStringParameters.name) {
    return {
      statusCode: 200,
      body: JSON.stringify(
        {
          message: `Hi, ${event.queryStringParameters.name}!`
        },
        null,
        2
      )
    };
  }
  return {
    statusCode: 200,
    body: JSON.stringify(
      {
        message: `Hi, there!`
      },
      null,
      2
    )
  };
};

Now if you will hit the below URL, you should receive output as below

https://some-random-text.execute-api.us-east-1.amazonaws.com/dev/hello?name=Sanket

{
  "message": "Hi, Sanket!"
}

Creating POST endpoint

You can configure the function(let say submitForm) as POST in serverless.yml as below

functions:
  hello:
    handler: handler.hello
    events:
      - http:
          path: hello
          method: get
  # POST endpoint
  submitForm:
    handler: handler.submitForm
    events:
      - http:
          path: submitForm
          method: post

The submitForm function will be

module.exports.submitForm = async event => {
  if (event.body) {
    return {
      statusCode: 200,
      body: JSON.stringify(
        {
          data: JSON.parse(event.body)
        },
        null,
        2
      )
    };
  }

  return {
    statusCode: 200,
    body: JSON.stringify(
      {
        message: "Received nothing"
      },
      null,
      2
    )
  };
};