Monitoring Nginx

To monitor the Nginx server using Prometheus, there are two components:

1. Enable stub_status in the Nginx container.

2. Run nginx-prometheus-exporter in a separate container to gather Nginx data and expose these metrics in a format usable by Prometheus.

Enable stub_status in Nginx

In the nginx.conf file, add a location (the path is arbitrary, typically /stub_status, /nginx_status, or /status):

http {
    server {
        listen 80;
        ...

        # This location is scraped by Prometheus
        location /nginx_status {
            stub_status;
            allow 127.0.0.1;
            allow ::1;             # IPv6 localhost
            allow nginx-exporter;  # metrics scraper and adapter
            deny all;
        }

In allow I originally used a subnet mask of the Docker internal network (172.19.0.0/16) but that is installation-dependent. Instead I use the container name (nginx-exporter) which Docker's DNS resolves to the IP address on the bridge network.

Another solution is to use a "network alias" or "host alias" in the network definition (docker-compose).

Using a network alias of "nginx-metrics":

• In docker-compose.yml

  networks:
    app-net:
      aliases:
        - nginx-metrics

• In nginx.conf

  location /nginx_status {
      stub_status;
      allow metrics-collector;
      deny all;
  }

Create Container for nginx-prometheus-exporter

In docker-compose.yml

  nginx-exporter:
    # Export server metrics for monitoring via Prometheus.
    image: nginx/nginx-prometheus-exporter
    container_name: nginx_exporter
    ports:
       # no need to expose a port
       # - "9113:9113"
    command:
       - '-nginx.scrape-uri=http://nginx:80/nginx_status'
    depends_on:
      - nginx
    networks:
      - app-net

Note: to save time at start-up I run docker pull nginx/nginx-prometheus-exporter in advance.

Verification

Test that the name "nginx-exporter" is resolvable in the nginx container. On the host where you are running Docker:

# Exec into nginx container and test DNS resolution
docker exec -it nginx nslookup nginx-exporter

To verify that metrics scraping is working, temporarily expose port 9113 and browse to http://localhost:9113/metrics. Use curl or a web browser.