Simple AWS Lambda Function to store a simple feed of text data in Redis

index.js

/*
    This was written to provide a simple serverless backend for a widget which displays live updating comments on a signup page. 
    The frontend can simple call $.post to add a comment, and $.get to retrieve the latest comments.
    You need a Redis instance somewhere, you can get a free 30MB one from Redis Labs.
    You'll also need to configure a AWS API Gateway endpoint which invokes this function for GET and POST requests
*/

'use strict';

const redis = require('redis'); // You'll need to upload Redis in node_modules. Easiest way to do this is do npm install redis --save in a blank directory, zip it and then upload to Lambda

exports.handler = (event, context, callback) => {
    
    var redisClient = redis.createClient(process.env.REDIS_URL)
    const done = (err, res) => callback(null, {
        statusCode: err ? '400' : '200',
        body: err ? err.message : JSON.stringify(res),
        headers: {
            'Content-Type': 'application/json',
            "Access-Control-Allow-Origin" : "*"
        },
    });

    const getComments = () => {
      redisClient.lrange('comments', 0, 9, (err, reply) => {
          done(null, {comments: reply});
          redisClient.quit();
      });
    }

    const postComment = (body) => {
        redisClient.lpush('comments', body.comment, (err, reply) => {
          redisClient.ltrim('comments', 0, 49, (err, reply) => {
              done(null, {})
              redisClient.quit()
          })
        });
    }
    
    switch (event.httpMethod) {
        case 'GET':
            getComments();
            break;
        case 'POST':
            postComment(JSON.parse(event.body));
            break;
        default:
            done(new Error(`Unsupported method "${event.httpMethod}"`));
    }

};