docs: prometheus howto

docs/prometheus.md

@@ -0,0 +1,41 @@
+# Prometheus howto
+
+Create a `prometheus.yml` file:
+
+```
+scrape_configs:
+- job_name: myapp
+  scrape_interval: 10s
+  static_configs:
+  - targets:
+    - 172.18.0.2:8888
+    - 172.18.0.3:8888
+    - 172.18.0.4:8888
+    - 172.18.0.6:8888
+```
+
+Replace the IP addrs under `targets` to the actual IP addrs of the worker nodes
+in the cluster.
+
+
+Run the prometheus container:
+
+
+```bash
+docker run --network host -p 9090:9090 -v $PWD/prometheus.yml:/etc/prometheus/prometheus.yml prom/prometheus &
+```
+
+
+Point browser to the IP addr of the node where prometheus is running:
+
+```
+http://<prometheus node IP addr>:9090
+```
+
+
+Another simple test to see if prometheus is working:
+
+
+```bash
+$ curl http://<worker node IP addr>:8888/metrics
+```