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Service Metrics

Now that Prometheus and Grafana are configured and monitoring the operating system, let's configure Linko to expose application-specific metrics. Prometheus provides official Go support via github.com/prometheus/client_golang/prometheus.

Configuring a Go web app to export Prometheus metrics is straightforward. We'll use the github.com/prometheus/client_golang/prometheus/promhttp package, which provides an HTTP handler we can register on an endpoint of our choice. /metrics is the common convention.

mux.Handle("GET /metrics", promhttp.Handler())

That line registers the promhttp.Handler() to respond to GET requests on /metrics.

Assignment

Update Prometheus and Grafana to monitor Linko's application metrics.

Add a GET /metrics endpoint to Linko, using promhttp.Handler().
Start Linko:
```
go run .
```
Configure Prometheus to query Linko by adding a new scrape job to prometheus.yml:
```
- job_name: linko
  static_configs:
    - targets: ["host.docker.internal:8899"]
```
for Windows (WSL2) users

If you're on WSL2 and the linko target stays DOWN, replace host.docker.internal with your WSL IP from hostname -I.
Because Prometheus runs in Docker and Linko runs on your host machine, add extra_hosts to the Prometheus service in docker-compose.yaml so it can reach your host:
```
extra_hosts:
  - "host.docker.internal:host-gateway"
```
Restart the Prometheus container to pick up the new configuration:
```
docker compose up
```
Wait at least 10 seconds, then query Prometheus to see if you can get Go's garbage collection stats from Linko to confirm it's working:
```
go_gc_duration_seconds_sum{job="linko"}
```

Run and submit the CLI tests from the root of the Linko repo.

Service Metrics

Assignment

for Windows (WSL2) users