make runtime configurable

[JamesKyburz]

Make runtime configurable.

• use runtime from provider as default (is present)
• allow specific runtime in custom configuration
• support for custom runtimes

I have deployed a test lambda with the updated code, and warmup worked using a custom runtime.

[juanjoDiaz]

Hi @JamesKyburz ,

Thanks for your contribution. A couple of questions:

What's the use case for using a custom runtime or the runtime of the provider?
The warmup lambda is created for a specific node.js runtime. Of course, using a higher node.js runtime should work, but using an older node version or using python, java, or something else would not. And there are many users using such runtimes.
So I can see a lots of room for things not working and people raising tickets and very little benefits, unless I'm missing some obvious benefit...

I can also see that you have sneaked in support for layers. Layers support was discussed on #142 and it was decided that there is no reason to support them since, as mentioned, the warmup lambda is a custom self-contained lambda that shouldn't be tampered with.

[JamesKyburz]

Thanks for the feedback. You are right that I was not thinking about older versions of node :)

The use case I personally have is the ability to configure the warmup functions to use the same custom javascript runtime as all my other javascript functions.

So this pull request makes it possible to use node12 or a custom runtime (that's why I added layers too)

If the code is designed to run on node10 I could maybe remove reading the runtime from the provider block in serverless.yml?

[juanjoDiaz]

I guess that the question is whether there is any benefit on having the warmup lambda using the same runtime as your other lambdas or even a custom runtime. And AFAIK the answer is no. Or is there any?

I'd only see any value on this if, for example, we would allow external warmup function as was requested in #93. At the same time, if you do that you might as well just create the function using normal serverless and skip this plugin completely.

[JamesKyburz]

Having the ability to use a custom runtime has two advantages imho cost and monitoring.

Switching to a custom runtime can be cheaper than waiting for Amazon to release their official runtime (node 12 lts is soon and we will have to wait a while for Amazon's version)

If a company uses custom runtimes for example nsolid from nodesource then all lambdas including warmup ones can be monitored the same way.

[JamesKyburz]

Rebased with the latest, Added a few style changes since npm run lint failed with the latest changes in master.

[JamesKyburz]

I removed the style changes! I was running a different version of eslint locally after the rebase :)

[juanjoDiaz]

Closing since this seems unnecessary and no one else is requesting to configure the runtime.
We can bring this back if it ever becomes necessary.