Add guide for pprof endpoints

Signed-off-by: Hidde Beydals <hello@hidde.co>

docs/dev-guides/debugging.md

@@ -0,0 +1,35 @@
+# Advanced debugging
+
+This guide covers more advanced debugging topics such as collecting
+runtime profiling data from GitOps Toolkit components.
+
+As a user, this page normally should be a last resort, but you may
+be asked by a maintainer to share a [collected profile](#collecting-a-profile)
+to debug e.g. performance issues.
+
+## Pprof
+
+The [GitOps Toolkit components](../components/index.md) serve [`pprof`](https://golang.org/pkg/net/http/pprof/)
+runtime profiling data on their metrics HTTP server (default `:8080`).
+
+### Endpoints
+
+| | Path |
+|-------------|------------------------|
+| Index | `/debug/pprof/` |
+| CPU profile | `/debug/pprof/profile` |
+| Symbol | `/debug/pprof/symbol` |
+| Trace | `/debug/pprof/trace` |
+
+### Collecting a profile
+
+To collect a profile, port-forward to the component's metrics endpoint and
+collect the data from the [endpoint](#endpoints) of choice:
+
+```console
+$ kubectl port-forward -n <namespace> deploy/<component> 8080
+$ curl -Sk -v http://localhost:8080/debug/pprof/heap > heap.out
+```
+
+The collected profile [can be analyzed using `go`](https://blog.golang.org/pprof),
+or shared with one of the maintainers.