Add metrics service backed by Prometheus

- This is the first step towards adding some observability into the backend server
- For now, the Prometheus service just monitors itself, scraping metrics at the default rate of once per minute
- v2.53 is the current LTS build, which will be supported until 2025-07-31
  - https://prometheus.io/docs/introduction/release-cycle/
- Ad-hoc queries can be run against the dev service via the web UI at http://localhost:9090 or against the remote host by creating an ssh tunnel and then hitting the same website
  - `ssh -L 9090:localhost:9090 org -N`
- https://prometheus.io
- https://prometheus.io/docs/prometheus/latest/installation/#using-docker
- https://prometheus.io/docs/prometheus/latest/getting_started/
- https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config

Author: High5Apps

ARCHITECTURE.md

@@ -37,6 +37,10 @@ Certbot sevice for renewing Let's Encrypt TLS certificates.
 
 For load testing the server using the Apache JMeter application and CLI.
 
+### `metrics`
+
+[Prometheus](https://prometheus.io/) service for collecting metrics, running ad-hoc queries, and managing alerts. 
+
 ### `site`
 
 The root of the Ruby on Rails site service. It serves the static website at <https://getorganize.app>. It follows [Rails conventions](https://github.com/jwipeout/rails-directory-structure-guide) for its subdirectory structure.

compose.yaml

@@ -32,6 +32,15 @@ services:
     restart: always
     volumes:
       - db-data:/var/lib/postgresql:rw
+  metrics:
+    build:
+      context: metrics
+    image: localhost:5001/organize-metrics
+    ports:
+      - "127.0.0.1:9090:9090"
+    restart: always
+    volumes:
+      - metrics-data:/prometheus:rw
   site:
     build:
       context: site
@@ -64,4 +73,5 @@ volumes:
   cert-conf:
   cert-www:
   db-data:
+  metrics-data:
   site-storage:

metrics/Dockerfile

@@ -0,0 +1,3 @@
+FROM prom/prometheus:v2.53.2
+
+COPY prometheus.yml /etc/prometheus/prometheus.yml

metrics/prometheus.yml

@@ -0,0 +1,4 @@
+scrape_configs:
+  - job_name: prometheus
+    static_configs:
+      - targets: ['localhost:9090']