api_setup.md

Setting up an API

Prerequisites

• AWS-Account
• Basic knowledge of either JS, Java or Python

How to

We are going to create a program which takes a min and max value and generates a random value in the range resulting from these two parameters

1. Creating the Lambda function

   1. Click the Create lambda function in your console
   2. Select the hello-world blueprint in the language of your choice (I'm gona be creating mine in nodejs6.10)
   3. We are not goingt to define the triggers just now
   4. Configure function
      • Name = "random number generator"
      • Runtime = Node . js 6.10
      • Code (Written in JS)

        'use strict';
        
        console.log('Loading function');
        
        exports.handler = (event, context, callback) => {
            // Minimum value of the random number
            let min = event.min;
            // Maximum value of the random number
            let max = event.max;
            // Calculating the number
            let generatedNumber = Math.floor((Math.random() * max) + min);
        
            callback(/*error message*/null, generatedNumber);
        };
        

      • Role = Create new role from template(s)
      • Role name = "basic-lambda-execute-role"
      • Policy templates: Simple Microservice permissions

2. Creating the API Gateway

   1. Click Create API in your API Gateway Console
   2. API name = "random-generator"
   3. In the Actions dropdown click Create Resource
      • Resource Name = "number"
   4. On the newly created number Resource, click the Actions dropdown again and select "Create Method"
   5. Set a GET method
      • Integration type = Lambda Function
      • Lambda Region = value of parameter "region" in link (.../home?region=us-east-1)
      • Lambda function = "random-number-generator"
   6. In the actions dropdown select Deploy API
      • Deployment stage = [New Stage]
      • Stage name = prod

3. Body Mapping

   1. Select the created "GET" Method under "Ressources" on your new API
   2. Click on "Integration Request"
   3. Expand "Body Mapping Template"
   4. "Add Mapping Template"
      • Content Type = "application/json"
   5. Write your template
      • Example

      {
      "_comment": "Takes a link in this form: '...?min=1&max=10'",
      "min" : "$input.params('min')",
      "max" : "$input.params('max')"
      }
      

   6. Deploy that shit