The Zot project is an open-source Docker image registry designed to be simple, efficient, and easy to use. As with any critical infrastructure component, monitoring is essential to ensure the registry’s health and performance. Prometheus, a leading open-source monitoring solution, can be integrated with Zot to collect and visualize metrics, providing insights into the registry’s operations.

In this article, we will walk through the steps to enable Prometheus metrics in the Zot project, ensuring you have the necessary observability to maintain a healthy Docker image registry.

Prerequisites

Before we begin, ensure you have the following:

1. A running instance of the Zot Docker image registry.
2. A Prometheus server set up and running.
3. Basic knowledge of Docker and Prometheus.

Step 1: Configure Zot for Prometheus Metrics

Zot provides built-in support for Prometheus metrics. To enable this feature, you need to modify the Zot configuration file. Here’s how you can do it:

1. Locate your Zot configuration file, typically named config.json.

2. Add or modify the metrics section in the configuration file to enable Prometheus metrics. Here is an example configuration:

   {
     "http": {
       "address": "0.0.0.0",
       "port": "5000"
     },
     "storage": {
       "rootDirectory": "/var/lib/zot"
     },
     "metrics": {
       "enable": true,
       "prometheus": {
         "path": "/metrics"
       }
     }
   }
   

   In this configuration, the metrics section is enabled, and Prometheus metrics are exposed at the /metrics endpoint.

3. Save the configuration file and restart the Zot service to apply the changes.

Step 2: Verify Zot Metrics Endpoint

Once Zot is configured to expose Prometheus metrics, verify that the metrics endpoint is accessible:

1. Open a web browser or use a tool like curl to access the metrics endpoint:

   curl http://<zot-server-address>:5000/metrics
   

2. You should see a list of metrics in Prometheus format. If you encounter any issues, double-check the configuration file and ensure Zot has been restarted.

Step 3: Configure Prometheus to Scrape Zot Metrics

Now that Zot is exposing metrics, configure your Prometheus server to scrape these metrics:

1. Open your Prometheus configuration file, typically named prometheus.yml.

2. Add a new job under the scrape_configs section to scrape the Zot metrics:

   scrape_configs:
     - job_name: 'zot'
       static_configs:
         - targets: ['<zot-server-address>:5000']
   

   Replace <zot-server-address> with the actual address of your Zot server.

3. Save the configuration file and restart the Prometheus server to apply the changes.

Step 4: Visualize Zot Metrics

With Prometheus now scraping metrics from Zot, you can visualize these metrics using Prometheus’s built-in graphing capabilities or integrate with Grafana for more advanced dashboards.

1. Access the Prometheus web UI by navigating to http://<prometheus-server-address>:9090.

2. Use the “Graph” tab to query and visualize metrics. For example, you can query zot_http_requests_total to see the total number of HTTP requests handled by Zot.

3. For more advanced visualization, consider setting up Grafana and adding Prometheus as a data source. You can then create custom dashboards to monitor Zot metrics effectively.

Conclusion

By enabling Prometheus metrics in the Zot project, you gain valuable insights into the performance and health of your Docker image registry. This setup allows you to proactively monitor and address potential issues, ensuring a reliable and efficient registry service.

For further reading and resources, consider the following:

• Zot Project GitHub Repository
• Prometheus Documentation
• Grafana Documentation

By leveraging open-source tools like Prometheus and Zot, you can build a robust and observable infrastructure that meets your container registry needs.