Add labels on a per-log basis to Stackdriver upload via Log4net

[williecohen-google]

Is your feature request related to a problem? Please describe.
I am using Log4net with the GoogleStackdriverAppender in a .NET framework project. I want to be able to add labels to our log entries for Cloud Monitoring. I want to be able to group logs easily using these labels (which is what their purpose seems to be). However, the GoogleStackdriverAppender only allows static custom labels to be added that apply to all logs flowing through the Appender.

Describe the solution you'd like
Ideally there would be a way to attach labels to certain logs, and not just statically for all logs generated. I'm assuming this decision was made to try and "fit" Log4net nicely into the Stackdriver data model, but I would think there would be a way to accommodate per log labels.

Describe alternatives you've considered

• Creating multiple appenders. (Seems like a terrible idea?)
• Creating structured logs to create our own labels at the proto payload level. (Seems like a band aid fix)

[amanda-tarafa]

I'll take a look at whether we can do this and how, but just to set expectations, I won't get to it for at least a couple of weeks.

[williecohen-google]

Any updates? We are running into log query latency issues and using log labels would speed things up dramatically (because they are indexed).

[jskeet]

@williecohen-google: Sorry, not yet - we'll try to have a look next week.

[amanda-tarafa]

I'm working on this, will have an update early next week.

[amanda-tarafa]

I believe you can already achieve this using properties, custom labels and patterns for custom labels.

• Configure the GoogleStackdriverAppender to use patterns for custom labels by setting the UsePatternWithinCustomLabels property to true.
• Add costume labels that use patterns to reference properties, like such:
  { "userName", "%property{userName}" }
• Use any of the log4net GlobaContext, ThreadContext and LogicalThreadContext to set properties.

The only caveat is that if a property is not set, the pattern will return "(null)", so the label will always be set but with a "(null)" value in some instances. Either you filter out the ones with "(null)" values, or we could consider adding a StripNullValuedLabels property to the appender so that we can remove such labels if they existed.

Let me know if this sounds reasonable to you.

[williecohen-google]

Ok, I think this sounds reasonable. We have a default label, which we could set at GlobalContext to prevent null values, but it would probably be nice for other use cases to strip nulls out. I'll try this out and see if I run into any issues. Thanks!

[williecohen-google]

Ok I was able to successfully add log labels with this! I do think for a follow up:

1. This should be documented somewhere (which maybe I missed).
2. Adding a StripNullValuedLabels property would be useful for adding labels to select logs.

Thanks for looking into this!

[amanda-tarafa]

Thanks for confirming that this solves your issue.

1. I'll make sure to add some docs/samples around this.
2. We'll look int it.

I'll keep open until I've added the docs at least.

[amanda-tarafa]

I've added documentation on how to translate Log4Net properties into labels. You can find it here.

As for the StripNullValuedLabels property, I've moved this issue to our backlog in #5628 to wait for more user demand.

I'll be closing this issue now since we've done as much as we are planning to do for now, but do please add another comment if you think there's something else we can do.