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Using Prometheus Recording Rules

Prometheus is a great way to collect a variety of metrics for your servers and applications. However, sometimes you need to perform calculations on the raw data Prometheus collects in order to gain actionable information. While queries can help you do this, recording rules provide an additional layer of optimization by allowing you to periodically pre-calculate query results and save them. In this lab, you will have the opportunity to implement some basic recording rules. This will provide you with some hands-on familiarity with the process of creating and managing recording rules.

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Lab platform
Lab Info
Level
Intermediate
Last updated
Jun 09, 2025
Duration
45m

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Table of Contents
  1. Challenge

    Implement a Recording Rule to Pre-Calculate CPU Usage
    1. Log in to the Prometheus server.

    2. Create a directory to store rules files:

      sudo mkdir -p /etc/prometheus/rules
      
    3. Edit the Prometheus config and add a rules location:

      sudo vi /etc/prometheus/prometheus.yml
      
      ...
      
      rule_files:
        - "/etc/prometheus/rules/*.yml"
      
      ...
      
    4. Create a rules file for limedrop-gateway server metrics:

      sudo vi /etc/prometheus/rules/limedrop-gateway.yml
      
    5. Implement a recording rule to pre-calculate CPU usage for the server:

      groups:
      - name: limedrop_gateway
        rules:
        - record: limedrop_gateway:cpu_usage
          expr: sum(rate(node_cpu_seconds_total{instance='limedrop-gateway:9100',mode!='idle'}[5m])) * 100 / 2
      
    6. Restart Prometheus to load the new configuration:

      sudo systemctl restart prometheus
      
    7. Access the expression browser (http://<PROMETHEUS_SERVER_PUBLIC_IP>:9090/graph) and run a query to verify you can see the pre-calculated data:

      limedrop_gateway:cpu_usage[5m]
      
  2. Challenge

    Add a Recording Rule to Pre-Calculate Memory Usage
    1. Edit the rules file:

      sudo vi /etc/prometheus/rules/limedrop-gateway.yml
      
    2. Add a recording rule to pre-calculate memory usage for the server:

      groups:
      - name: limedrop_gateway
        rules:
        - record: limedrop_gateway:cpu_usage
          expr: sum(rate(node_cpu_seconds_total{instance='limedrop-gateway:9100',mode!='idle'}[5m])) * 100 / 2
        - record: limedrop_gateway:memory_usage
          expr: 100 - (node_memory_MemAvailable_bytes{instance='limedrop-gateway:9100'} / node_memory_MemTotal_bytes{instance='limedrop-gateway:9100'}) * 100
      
    3. Restart Prometheus to load the new configuration:

      sudo systemctl restart prometheus
      
    4. Access the expression browser (http://<PROMETHEUS_SERVER_PUBLIC_IP>:9090/graph) and run a query to verify you can see the pre-calculated data:

      limedrop_gateway:memory_usage[5m]
      
    5. You can also check out the rules interface (http://<PROMETHEUS_SERVER_PUBLIC_IP>:9090/rules) to see the status of your rules.

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