And that's why attempting to keep lambdas warm is a waste of effort and money.
If your service gets steady traffic and your code is optimized for restarts, cold starts should be a non issue.
You could have the warm up handler sleep for a few seconds so Lambda is more likely to spin up some new capacity. This is no different than keeping some idle capacity on hand to absorb spikes.
Not every service gets steady traffic, even ones where latency is important.
Also, it's not always a matter of optimal start up time because even applications with instant start time have to be deployed by the Lambda service before they can respond. That can take up to a full minute, if I recall the documentation correctly.
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