luafanti / elasticache-redis-and-lambda

ElastiCache Redis & TypeScript Lambda - API caching demo

ElastiCache Redis & TypeScript Lambda - API caching demo

This repository contains an example of using in serverless application Redis to cache external API responses.

Code source is a part of my Dev.to article in which you can fine more info about the solution.

Deployment Overview

The infrastructure in demo is provisioned using the CloudFormation template. The stack created with the default parameters will provide the following resources:

• VPC with single public & private subnet, and other base VPC components
• NAT Gateway
• ElastiCache Redis
• TypeScript Lambda & HTTP API Gateway

⚠️ Please note that your stack includes components (NAT & Redis) that will incur hourly costs even if you have AWS Free Tier.

You can also create a stack in MultiAZ mode. Then the stack will create:

• VPC with two public and two private subnets
• 2 NAT Gateway, one per private subnet
• ElastiCache Redis in Multi-AZ mode - one master and one replica instance
• this same TypeScript Lambda

⚠️⚠️⚠️ In Multi-AZ mode costs will be doubled due to two instances of NAT and Redis

Installation

npm install 
sam build
sam deploy 

To remove whole stack

sam delete

Step-by-Step caching flow

Flow is very simply... ProxyLambda first checks if response from External API exists in cache. As a cache key in this simple example, I just use the full request path also with query params. In complex API I can recommend a more advanced strategy for key generation. If response object exists in Redis cache, Lambda returns it directly. Otherwise, Lambda calls External API as before but additionally saves this response to the Redis cache. Thanks to this, a subsequent request to ProxyLambda for this same resource, will be returned from cache instead calling External API.

Basically the two diagrams below should explain it all

There is still the question about invalidating records in cache. Here the strategy must fit requirements. In this demo, objects in the cache are eternal. One of solution would be to hardcode expiration time on save (redis.setEx(cacheKey, 86400, apiResponse). A more elegant way would be to create dedicated invalidation Lambda, which will remove objects from the cache when receiving an event that in External API some resource has been removed or modified.