Determining if a function invocation is a "cold start" can be quite helpful in troubleshooting a metric like latency.

Requirements

You must use the following versions of IOpipe client for cold start reporting to work properly:

What are cold starts?

Cold starts are essentially an invocation that takes longer to start up due to initialization of a container.

Even though it's called "serverless", there are of course servers under the hood.  In AWS Lambda, containers are used under the hood to run your functions.  Spinning up a new container is fast, but not as fast as an already warmed up container, nor as efficient to do for every single invocation.  

So in order to provide low latency, AWS Lambda re-uses containers for your active Lambda functions so that they doesn't have to "warm up" by loading dependencies or other resources each time they are invoked. 

When do cold starts happen?

  • Each time a new function or version is deployed it will incur a cold start.
  • If a function has been inactive for a period of time, the "warm" container may be shut down.  We are currently investigating this, but it is around 5 minutes of inactivity.
  • When you have a sudden spike of invocations to a function, AWS Lambda will spin up additional containers to scale automatically.  Each new container spun up will incur a cold start.
  • We've identified that cold starts happen every 2-4 hours regardless of activity.  AWS Lambda does some re-shuffling of resources to keep things running efficiently.  

What are the effects of a cold start?

Cold starts will incur a higher latency to any request, as it takes time to initialize the container and pull in any dependencies before running your function.  The amount of added latency can vary greatly depending on many factors.  The largest factor tends to be pulling in external resources, and  large dependencies loading.

How can I find cold starts with IOpipe?

You can see which invocations are a cold start by going to the function page in the IOpipe Dashboard, and looking at the invocation list.   You can also filter by cold starts.

You can also see if an specific invocation is a cold start in the invocation page

If you’d like to try this new feature out, we have a 2-week free trial, and this feature extends to all of our plans, including forever free.

If you have any questions, or find any out of date information please drop us a line at support@iopipe.com or Slack.

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