Google Cloud Function with minimum instances: cold start after every deployment?

Question

To minimize cold starts, I've set a minimum instance for my Google Cloud Function. I actually do it with the firebase admin SDK like this:

functions.runWith({ minInstances: 1 })

...but I can see it confirmed in Google Cloud Console:

I'm noticing that after every deployment, I still encounter one cold start. I would have assumed that one instance would be primed and ready for the first request, but that doesn't seem to be the case. For example, here are the logs:

You can see that ~16 hours after deployment, the first request comes in. It's a cold start that takes 8139ms. The next request comes in about another hour later, but there's no cold start and the request takes 556ms, significantly faster than the first request.

So is this the expected behaviour? Do we still encounter one cold start even if minimum instances is set? Should I then be priming the cloud function after every deployment with a dummy request to prevent my users from encountering this first cold start?

Answer 1

Tl;dr: The first execution of a function that has minimum instances set is not technically a cold start, but probably will be slower than later executions of that instance.

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Minimum instances of a function will immediately be "warmed up" on deploy and in a warm but idle state, ready to respond to a request. However, the functions we write often need to do extra setup work when they're actually triggered for the first time.

For example, we may use dynamic imports to pull in a library or need to set up a connection to a remote DB. Even though the function instance is warm, the extra work that has to be done on the first execution means that it will probably be slower than later executions.

The benefit of the minimum instances setting is that later executions benefit from all the setup work done by the first execution, and can be much faster than if they were scaled back to zero and had to set themselves up all over again on the next request.

Update: Occasionally, an idle instance may be killed by the Cloud Functions backend. If this happens, another instance will be spun up immediately to meet the required minimum instances setting, but that new instance will need to go through its extra setup work again the first time it is triggered. However, this really shouldn't happen often.