add support for reporting to rollbar

[sumeet]

TODO:

• add rollbar access token from https://rollbar.com/Remind/empire/

[ejholmes]

https://github.com/remind101/stacks/pull/683#discussion_r114231716.

[sumeet]

ah shit, fixed!

[ejholmes]

Awesome. Looks good! Can you also add a line to CHANGELOG.md?

We're running this internally in our staging environment, I think we should give this a couple days and assuming no issues, we can merge.

[sumeet]

@ejholmes sweet, sounds good. all set!

[ejholmes]

Just adding some comments on my findings here:

It seems like a lot of errors end up getting grouped incorrectly in Rollbar. Originally thought that this may have been a bug in remind101/pkg/reporter/rollbar, and tried to test with 293bd7a, however, errors still got clumped together.

Digging a little deeper, I noticed that all of the errors that got clumped together shared the same stack. In stvp/rollbar the fingerprint that gets generated for the error only takes the stack into account:

func (s Stack) Fingerprint() string {
	hash := crc32.NewIEEE()
	for _, frame := range s {
		fmt.Fprintf(hash, "%s%s%d", frame.Filename, frame.Method, frame.Line)
	}
	return fmt.Sprintf("%x", hash.Sum32())
}

I think this is ok, but ideally the fingerprint would be a combination of stack and error class, but it looks like there's no way to easily inject a custom fingerprint into stvp/rollbar.