What is a serverless cold start, really?
A cold start is the extra time a serverless platform spends creating an execution environment before your code can handle a request: finding compute, starting an isolated sandbox, booting the language runtime, loading your code and running its top-level initialisation. A warm request reuses an environment that already exists, which is why the first request after idle can take 2–3 seconds and the…
Serverless functions experience a delay when they first receive a request, known as a cold start. This occurs because the platform must allocate resources, create an isolated execution environment, initiate the language runtime, load the deployment artifact, and run module-level initialisation before executing the handler. In contrast, a warm invocation reuses an existing environment, resulting in faster processing times.
The cold start process is influenced by the size of the code bundle, with larger bundles taking longer to load. Developers can reduce cold starts by minimizing code, lazy initialisation, using lighter runtimes, and keeping instances warm with provisioned concurrency or minimum instances. Although cold starts are not bugs, they are the cost of creating compute resources on demand, and developers can choose to optimize them based on their specific use cases.
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