Improve docs on passing args to node process

[pellebjerkestrand]

func start with -- "--prof" seems to do nothing. I, at least, can't find the resulting *.log file anywhere on my system.

Adding --prof to NODE_OPTIONS in local.settings.json results in an error message.

Relevant output snippet:

Azure Functions Core Tools
Core Tools Version:       4.0.4865 Commit hash: N/A  (64-bit)
Function Runtime Version: 4.12.2.19454

[2022-12-01T13:39:27.380Z] Language Worker Process exited. Pid=14562.
[2022-12-01T13:39:27.380Z] node exited with code 9 (0x9). .
[2022-12-01T13:39:27.390Z] node: --prof is not allowed in NODE_OPTIONS

Easy profiling of Node.js apps (https://nodejs.org/en/docs/guides/simple-profiling/) seems impossible, unless I'm missing something.

Please allow us to profile Node.js apps run with func start.

[pellebjerkestrand]

Same behavior with the most recent version I can get from npm.

Azure Functions Core Tools
Core Tools Version:       4.0.4895 Commit hash: N/A  (64-bit)
Function Runtime Version: 4.13.0.19486

[ejizba]

Hi @pellebjerkestrand the recommended way to modify the arguments to the node process is to use the languageWorkers__node__arguments setting. Here's at least one example in the docs: https://learn.microsoft.com/en-us/azure/azure-functions/functions-reference-node?tabs=v2-v3-v4-export%2Cv2-v3-v4-done%2Cv2%2Cv2-log-custom-telemetry%2Cv2-accessing-request-and-response%2Cwindows-setting-the-node-version#in-local-development-environment

[pellebjerkestrand]

Hi @pellebjerkestrand the recommended way to modify the arguments to the node process is to use the languageWorkers__node__arguments setting. Here's at least one example in the docs: https://learn.microsoft.com/en-us/azure/azure-functions/functions-reference-node?tabs=v2-v3-v4-export%2Cv2-v3-v4-done%2Cv2%2Cv2-log-custom-telemetry%2Cv2-accessing-request-and-response%2Cwindows-setting-the-node-version#in-local-development-environment

Thanks a lot! That was not easy to find.

[ejizba]

Yeah I agree it's a bit of a needle in a haystack and we've heard this feedback before. Moving the issue to the Node.js repo for follow up.

Do you have any suggestions of where you may have looked to find this information?

[pellebjerkestrand]

It felt natural to me that passing arguments to the node process could be done on the command line, so I was looking in func start's documentation. I found nothing, so I searched for lots of different versions of "azure-functions-core-tools" + "pass argument to node" + "func start" and so on. I found plenty of blog posts and answers on Stack Overflow mentioning both -- "--prof" and using NODE_OPTIONS in local.settings.json with people writing that at least one of those worked for them.

If using --prof in NODE_OPTIONS gave a hint at what can be done instead (use languageWorkers__node__arguments), that would be great.

I still think it's more ergonomic to be able to pass these arguments on the command line when using func start since I rarely want profiling to stick around for long (and I guarantee I will forget that it's on and keep it longer than needed).

[gunzip]

@ejizba According to the documentation, using languageWorkers__node__arguments can negatively impact cold start times because it forces the runtime to start a new worker from scratch instead of using pre-warmed ones.

Does setting arguments via NODE_OPTIONS have the same drawback?

I'm asking because using OTEL with ESM requires passing specific arguments to Node.js, as mentioned here: https://github.com/open-telemetry/opentelemetry-js/blob/main/doc/esm-support.md#additional-notes-on-experimental-loaders.

Thank you in advance!