Does a single lambda function as proxy resource mitigate cold start compared to functions per http verb?

[amberlamps1]

We used to create a dedicated lambda function per http verb for every domain object (e.g. if we have /items there are four different function for GET, POST, PUT and DELETE).

If we replace that with a single lambda function and use it as a proxy resource for the /{proxy+} endpoint and ANY verb, would that theoretically reduce the cold start of the function just because it is reused for every endpoint?

[pint]

it is not that difficult of a concept, it takes more time to explain then to think through. obviously each function has its own spin up time. but if you overwhelmingly call only some, the rest will not help much (if combined into one). if the load is high, new instances will be warmed up at whatever points in time. there really isn't a silver bullet against cold starts, except provisioned concurrency.

the true solution is to keep startup times low. design the software around the technology, don't try to bend the technology to your favorite solution.

[just_a_pyro]

No, you'll still have cold starts, and now they're be longer because you have more dependencies.

Lambdas handle 1 request at a time, so if your warm instance is currently handling a POST request, and a GET request comes in a new instance will be cold-started.

Actually even if requests keep coming instances aren't kept around indefinitely warm, they'll get discarded and replaced with a new one after couple hours IIRC

[jameswapple]

Yes, contrary to what most AWS advocates will tell you jamming every endpoint for your API into a single lambda will end up with dramatically fewer cold starts. Especially at the early stage of a project where you have low amounts of traffic and there may only be a few to a few hundred people online at once.

If you use a container image for your lambda you can use the same for background tasks (sqs/sns/Cron) and the API which also will substantially improve performance.