Prometheus: Deep Dive

These are the essential building blocks that enable Prometheus to deliver robust monitoring and alerting in cloud-native and traditional environments:

• Prometheus Server: The central component that scrapes and stores time-series data. It handles all the data collection, runs queries via PromQL, and manages built-in alerting.
• Data Exporters: Lightweight agents or programs that expose metrics in a format Prometheus understands. Exporters bridge the gap between systems that do not natively produce Prometheus metrics (for example, node_exporter for system metrics).
• Alertmanager: Handles all alert notifications generated by Prometheus rules. Alertmanager groups, de-duplicates, and routes alerts to email, Slack, or other channels based on user-defined policies.
• Service Discovery: Automated discovery of monitoring targets in dynamic environments. Prometheus can watch platforms such as Kubernetes or Consul to identify endpoints for scraping without manual updates.
• Web UI and Visualization: A built-in, browser-accessible interface for querying and viewing metrics, troubleshooting data, and exploring time-series trends. For advanced dashboards, Prometheus integrates with tools like Grafana.

Before deploying Prometheus, ensure the following prerequisites are met to enable a smooth and efficient installation:

• Supported Operating System: Prometheus can run on most Unix-based systems (Linux is preferred) and also supports Windows and macOS.
• System Requirements: For typical setups and small environments, allocate at least 2 CPU cores, 4 GB of RAM, and 20 GB of free disk space. Larger production deployments may need additional resources.
• Administrator Privileges: Ensure you have admin or root privileges to install software and configure services on the server where Prometheus will be installed.
• Network Access: Allow inbound TCP connections on port 9090, which is used for Prometheus’s web interface and APIs. Also ensure outbound internet access for downloads and updates.
• Create Dedicated User: For enhanced security, create a non-privileged system user and group (commonly named prometheus) to run the Prometheus process.
• Set Up Folders: Prepare directories for configuration files (such as /etc/prometheus) and data storage (such as /var/lib/prometheus).
• Basic Linux Knowledge: Familiarity with the terminal and basic Linux commands will be helpful during installation and configuration.

1. Update System Packages: Ensure your OS package repositories are up to date.
2. Download Prometheus Binaries: Get the latest release from the official Prometheus website or GitHub repository, matching your operating system and processor architecture.
3. Extract and Place Binaries: Unpack the archive and move the prometheus and promtool binaries to a location in your system’s PATH (such as /usr/local/bin).
4. Copy Console Libraries: Move the consoles and console_libraries directories (included in the download) to the configuration directory.
5. Initialize Configuration: Create an initial prometheus.yml file and tailor it to your desired monitoring targets.
6. Open Firewall Port: Adjust firewall rules to permit incoming connections on port 9090.

Once these prerequisites are in place, you are ready to proceed with the Prometheus installation and configuration steps.

After installing Prometheus, the next crucial step is configuring it to begin collecting and storing metrics. Configuration is managed via a YAML file typically named prometheus.yml. Below is a step-by-step guide to help you set up Prometheus for effective monitoring:

1. Locate the Configuration File: The default location for the Prometheus configuration file is /etc/prometheus/prometheus.yml. If you're using a different directory, ensure the path is correctly specified when running the Prometheus binary.
2. Define Global Settings: Start by setting global configuration parameters such as the scraping interval and evaluation interval:

   
   global:
     scrape_interval: 15s
     evaluation_interval: 15s
       

   These intervals determine how often Prometheus collects data and evaluates alerting rules.
3. Configure Scrape Targets: Scrape targets define which endpoints Prometheus should collect metrics from. Here’s an example configuration for a basic node exporter:

   
   scrape_configs:
     - job_name: 'node_exporter'
       static_configs:
         - targets: ['localhost:9100']
       

   This tells Prometheus to scrape metrics from the Node Exporter running on the local machine.
4. Add More Job Definitions: You can add multiple job definitions to scrape different sets of services or exporters. Each job can include static targets or use service discovery:

   
     - job_name: 'app_metrics'
       static_configs:
         - targets: ['app-server-1:8080', 'app-server-2:8080']
       

5. Use Service Discovery (Optional): For dynamic environments like Kubernetes, use service discovery to automatically discover scrape targets:

   
     - job_name: 'kubernetes-pods'
       kubernetes_sd_configs:
         - role: pod
       relabel_configs:
         - source_labels: [__meta_kubernetes_pod_annotation_prometheus_io_scrape]
           action: keep
           regex: true
       

6. Configure Alerting Rules: Prometheus supports custom alerts using the rule_files directive. Add rules to a separate YAML file and reference them:

   
   rule_files:
     - 'alert_rules.yml'
       

   These rules define conditions under which alerts should fire based on metrics measurements.
7. Validate and Restart: Use the promtool check config prometheus.yml command to validate your config file. Then restart the Prometheus service or rerun the binary to apply the new configuration.

Proper configuration ensures Prometheus scrapes the right targets, stores accurate metric data, and triggers alerts on performance or availability issues as needed.

Once Prometheus is installed and configured, it's important to validate that everything is working correctly. This step ensures your configuration file is error-free, Prometheus is running, and metrics are being scraped as expected. Follow the steps below to complete validation:

1. Step 1: Check Prometheus Status
   Run the following command to ensure Prometheus is running:

   systemctl status prometheus

   If you installed Prometheus as a systemd service, this command will confirm that it started successfully. You should see 'active (running)' in the output.
2. Step 2: Validate Configuration File
   Use the built-in Prometheus tool promtool to validate your configuration file:

   promtool check config /etc/prometheus/prometheus.yml

   This will check for proper YAML syntax and Prometheus-specific rules. If there are no errors, the output will confirm the file is valid.
3. Step 3: Open the Web UI
   Navigate to the Prometheus web interface by visiting:

   http://localhost:9090

   From here, you can access the built-in expression browser, list of targets, and alerting rules.
4. Step 4: Check Scrape Targets
   In the web UI, click on Status > Targets to view all configured scrape targets. Each target should display a green "up" status if successful. If any targets are marked as "down," revisit the configuration file to debug.
5. Step 5: Run a PromQL Query
   In the Prometheus web UI, try running a basic query in the "Expression" bar to confirm metrics are being collected:

   up

   This simple query checks the availability of each target and should return results with labels and status values.
6. Step 6: Monitor Logs for Errors
   If something seems off, review the Prometheus logs with the following command:

   journalctl -u prometheus -f

   Logs can help pinpoint configuration errors, failed scrapes, or permission issues.

Completing these validation steps ensures your Prometheus instance is operational and ready to collect meaningful metrics from your systems and applications.

Troubleshooting Prometheus involves systematically identifying and resolving issues to ensure continuous and reliable monitoring. Follow these step-by-step procedures if you encounter errors or system instability:

1. Check Prometheus Service Status
   Confirm whether Prometheus is running as expected:

   systemctl status prometheus

   If it shows as “failed” or “inactive,” continue to the next steps.
2. Review Logs for Error Details
   Examine real-time logs to find specific error messages or warnings:

   journalctl -u prometheus -f

   Look for issues like file permission errors, missing directories, or configuration problems.
3. Validate Configuration Files
   Configuration errors are a common cause of failure. Check your YAML files for mistakes:

   promtool check config /etc/prometheus/prometheus.yml

   Correct any highlighted syntax problems and restart the service if required.
4. Check File and Directory Permissions
   Prometheus needs proper access to its config files and data directories:

   ls -l /etc/prometheus/prometheus.yml
   ls -l /var/lib/prometheus/

   If needed, set the correct ownership:

   sudo chown -R prometheus:prometheus /etc/prometheus
   sudo chown -R prometheus:prometheus /var/lib/prometheus

5. Verify Storage and Disk Space
   Prometheus depends on adequate disk space for data retention. Running out of space can halt ingestion:

   df -h /var/lib/prometheus

   Free up space or expand storage if necessary.
6. Investigate High Resource Usage
   High memory or CPU usage can signal excessive data or inefficient queries.
   • Reduce scrape intervals or the number of metrics collected.
   • Review PromQL queries and avoid unfiltered metric selectors that can aggregate unnecessary data.
7. Address High Cardinality Issues
   Too many unique label combinations (cardinality) can overload Prometheus. Identify problematic metrics and remove or relabel high-cardinality labels where possible.

   topk(10, count by(__name__)({__name__=~".+"}))

8. Resolve Service Start Failures
   If Prometheus fails to start after repeated attempts, reset the service state:

   sudo systemctl reset-failed prometheus
   sudo systemctl start prometheus

9. Fix Alerting and Scraping Issues
   If alerts don’t fire or expected data is missing:
   • Check the Status > Targets section in the web UI to verify scrape targets are up.
   • Review alert rules for missing for durations, which can prevent transient issues from creating alert fatigue.
10. Handle Data Corruption
    If storage corruption is detected, you might need to remove or repair corrupted data blocks:

    promtool tsdb list

    Delete only the problematic blocks after backup to restore functionality.
11. Monitor and Maintain Regular Backups
    Frequent backups of your data directory are essential for recovery in case of major failures.

Follow this methodical troubleshooting process to swiftly resolve most Prometheus issues and keep your monitoring system healthy and dependable.