Are Cold Starts Really a Problem?īack to my original question on Twitter. If the clients were defined inside the main handler, you’d take the performance hit every time the function was executed, regardless of whether of not the function was warm. The thought process behind declaring things globally is that the initialization code only needs to be executed once for the entire lifecycle of a function container. This is one of the accepted trade-offs with serverless and there’s not much you can do about optimizing it. On the flip side, it adds to your cold start time because they are being setup during the function container initialization phase. This allows a function to reuse any connections it has established in subsequent runs. It is considered a best practice to define SDK clients and cacheable variables globally in a Lambda function. If you find yourself importing more and more resources in a single function, it might be time to reassess and evaluate using Step Functions instead to coordinate your workflow. So be careful when importing entire packages instead of the specific components you need from it. When you add more imports to a function, the runtime must resolve the dependencies, which adds to the cold start time. They found that as function package size increases, cold start duration increases, even if additional dependencies aren’t being consumed!Ĭold start comparison of package sizes. ![]() ![]() Package SizeĪ great case study was performed by Lumigo around performance impact of cold starts as it relates to package size and importing of dependencies. Once function containers have warmed up, performance converges to roughly the same duration between compiled and interpreted languages. NET have slower cold starts compared to interpreted languages like Python, Go, and Node. According to research from Thundra, Java has the slowest cold start duration by 7x compared to the second slowest. It is the slowest runtime for cold starts. If Java is your runtime of choice, I have bad news. Startup Logic - The connections and initializations defined outside of the main handler in your function.Package Size - The amount of data that needs to be loaded to run your code.Runtime - The programming language you are using.There are a few things that directly impact the duration of a cold start: Applications with a sustained amount of usage throughout the day will see fewer cold starts once Lambda has scaled up to the appropriate amount of concurrent execution environments. With this in mind, some applications are more prone to cold starts than others. This results in cold starts as Lambda begins to scale to match the increased demand. Traffic bursts refer to points throughout the day with minimal usage followed by a big spike in traffic. ![]() This means it can happen when users start logging into your application for the day or when a burst of traffic comes through. Lambda must initialize a new container to execute your code and that initialization takes time - hence cold starts. What Are Cold Starts?Ĭold starts occur on the first request to invoke your function or when the Lambda runtime environment is busy processing your business logic. Let’s dive in and see if we can put this argument to bed once and for all. There are exceptions of course, but most of the exceptions have valid workarounds. I received a variety of answers, but the most common response I saw was “ it’s not a real problem in production”. So I asked a probing question on Twitter.Ĭan someone give me an example where #lambda function cold starts gave you legitimate issues in production?- Allen Helton August 26, 2022 They heard about them a few years ago and have latched onto the idea that as long as they exist, serverless is a non-starter for them. She latched onto an idea, generalized it, and now was too worked up to try anything related.Įvery presentation I’ve given on serverless someone has brought up cold starts. If it wasn’t a solid, it was sauce and she would reject it. Ever since then anything that looked like sauce was a no go for her. See, a few months ago we had a meal with a glaze on it that she…. Naturally, I ask her why to which she responds “it has sauce on it.” My four year old looked at her plate and said to me “I don’t want this chicken.” ![]() I was eating dinner the other day with my family.
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