feature: add before/after InvocationRequest hooks

[markwolff]

Adds two InvocationRequest hooks to WorkerChannel to enable context correlation and node.js worker APM instrumentation. Sample use case for Azure Monitor node.js SDK.

• invocationRequestBefore: (context, userFunction) => contextWrappedUserFunction
• invocationRequestAfter: () => void

note: workerChannel would need to be passed to app insights in some way, i.e. in nodejsWorker.ts:

if (shouldSetupAppInsightsFunctionsIntegration) {
  require("/path/to/applicationinsights/agent/functions")
    .setupFunctionsInvocationHooks(workerChannel);
}

In App Insights SDK, setupFunctionsInvocationHooks would be defined:

workerChannel.invocationRequestBefore = (context, userFunction) => {
    // Map Functions context to AppInsights context
    const correlationContext = appInsights.startOperation(context, "Functions.JavaScript.Trigger");

    // Wrap the Function runtime with correlationContext
    return appInsights.wrapWithCorrelationContext(userFunction, correlationContext);
}

workerChannel.invocationRequestAfter = () => {
    // Do any extra cleanup or flushing here
    appInsights.defaultClient.flush(); // can be async or sync
}

[lzchen]

Curious as to why context isn't exposed in After as well.

[markwolff]

Agree. It seems like it would be required to correlate internal logging with the trace context

[lzchen]

Are we able to call this.invocationRequestAfter(); at the end of this whole function? Instead of putting multiple separate calls for possible outcomes of the result (regular, catching errors, catch outstanding errors).

[markwolff]

These are all happening in separate async paths which never converge on completion. I could see adding some this.finish() to each path to converge them. And within that we could call invocationRequestAfter(), but this would look pretty similar to what is already there. wdyt?

[lzchen]

this.finish() would be more elegant but not really a blocking issue :)

[lzchen]

note: workerChannel would need to be passed to app insights in some way, i.e. in nodejsWorker.ts:

Instead of needing to pass in the workerChannel, why not expose some api to add a callback which would BE the actual before/after functions?