Is AWS Lambda good for real-time API Rest?

Question

I'm learning about AWS Lambda and I'm worried about synchronized real-time requests. The fact the lambda has a "cold start" it doesn't sounds good for handling GET petitions.

Imagine a user is using the application and do a GET HTTP Request to get a Product or a list of Products, if the lambda is sleeping, then it will take 10 seconds to respond, I don't see this as an acceptable response time. Is it good or bad practice to use AWS Lambda for classic (sync responses) API Rest?

Answer 1

Like most things, I think you should measure before deciding. A lot of AWS customers use Lambda as the back-end for their webapps quite successfully.

There's a lot of discussion out there on Lambda latency, for example:

• 2017-04 comparing Lambda performance using Node.js, Java, C# or Python
• 2018-03 Lambda call latency
• 2019-09 improved VPC networking for AWS Lambda
• 2019-10 you're thinking about cold starts all wrong

In December 2019, AWS Lambda introduced Provisioned Concurrency, which improves things. See:

• 2019-12 AWS Lambda announces Provisioned Concurrency
• 2020-09 AWS Lambda Cold Starts: Solving the Problem

You should measure latency for an environment that's representative of your app and its use.

A few things that are important factors related to request latency:

• cold starts => higher latency
• request patterns are important factors in cold starts
• if you need to deploy in VPC (attachment of ENI => higher cold start latency)
• using CloudFront --> API Gateway --> Lambda (more layers => higher latency)
• choice of programming language (Java likely highest cold-start latency, Go lowest)
• size of Lambda environment (more RAM => more CPU => faster)
• Lambda account and concurrency limits
• pre-warming strategy

Update 2019-12: see Predictable start-up times with Provisioned Concurrency.

Update 2021-08: see Increasing performance of Java AWS Lambda functions using tiered compilation.