Lambda Warmer: Optimize AWS Lambda Function Cold Starts

At a recent AWS Startup Day event in Boston, MA, Chris Munns, the Senior Developer Advocate for Serverless at AWS, discussed Lambda cold starts and how to mitigate them. According to Chris (although he acknowledge that it is a “hack”) using the CloudWatch Events “ping” method is really the only way to do it right now. He gave a number of really good tips to pre-warm your functions “correctly”:

  • Don’t ping more often than every 5 minutes
  • Invoke the function directly (i.e. don’t use API Gateway to invoke it)
  • Pass in a test payload that can be identified as such
  • Create handler logic that replies accordingly without running the whole function

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Solving the Cold Start Problem

Dear AWS Lambda Team,

I have a serious problem: I love AWS Lambda! In fact, I love it so much that I’ve pretty much gone all in on this whole #serverless thing. I use Lambda for almost everything now. I use it to build backend data processing pipelines, distribute long running tasks, and respond to API requests. Heck, I even built an Alexa app just for fun. I found myself building so many RESTful APIs using Lambda and API Gateway that I went ahead and created the open source Lambda API web framework to allow users to more efficiently route and respond to API Gateway requests.

Serverless technologies, like Lambda, have revolutionized how developers think about building applications. Abstracting away the underlying compute layer and replacing it with on-demand, near-infinitely scalable function containers is brilliant. As we would say out here in Boston, “you guys are wicked smaht.” But I think you missed something very important. In your efforts to conform to the “pay only for the compute time you consume” promise of serverless, you inadvertently handicapped the service. My biggest complaint, and the number one objection that I hear from most of the “serverless-is-not-ready-for-primetime” naysayers, are Cold Starts.

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