Prometheus Configuration

Complete guide to Prometheus setup, metric collection, scrape configuration, and recording rules.

Purpose

Configure Prometheus for comprehensive metric collection, alerting, and monitoring of infrastructure and applications.

When to Use

• Set up Prometheus monitoring
• Configure metric scraping
• Create recording rules
• Design alert rules
• Implement service discovery

Prometheus Architecture

┌──────────────┐
│ Applications │ ← Instrumented with client libraries
└──────┬───────┘
       │ /metrics endpoint
       ↓
┌──────────────┐
│  Prometheus  │ ← Scrapes metrics periodically
│    Server    │
└──────┬───────┘
       │
       ├─→ AlertManager (alerts)
       ├─→ Grafana (visualization)
       └─→ Long-term storage (Thanos/Cortex)

Installation

Kubernetes with Helm

helm repo add prometheus-community https://prometheus-community.github.io/helm-charts
helm repo update

helm install prometheus prometheus-community/kube-prometheus-stack \
  --namespace monitoring \
  --create-namespace \
  --set prometheus.prometheusSpec.retention=30d \
  --set prometheus.prometheusSpec.storageVolumeSize=50Gi

Docker Compose

version: "3.8"
services:
  prometheus:
    image: prom/prometheus:latest
    ports:
      - "9090:9090"
    volumes:
      - ./prometheus.yml:/etc/prometheus/prometheus.yml
      - prometheus-data:/prometheus
    command:
      - "--config.file=/etc/prometheus/prometheus.yml"
      - "--storage.tsdb.path=/prometheus"
      - "--storage.tsdb.retention.time=30d"

volumes:
  prometheus-data:

Configuration File

prometheus.yml:

global:
  scrape_interval: 15s
  evaluation_interval: 15s
  external_labels:
    cluster: "production"
    region: "us-west-2"

# Alertmanager configuration
alerting:
  alertmanagers:
    - static_configs:
        - targets:
            - alertmanager:9093

# Load rules files
rule_files:
  - /etc/prometheus/rules/*.yml

# Scrape configurations
scrape_configs:
  # Prometheus itself
  - job_name: "prometheus"
    static_configs:
      - targets: ["localhost:9090"]

  # Node exporters
  - job_name: "node-exporter"
    static_configs:
      - targets:
          - "node1:9100"
          - "node2:9100"
          - "node3:9100"
    relabel_configs:
      - source_labels: [__address__]
        target_label: instance
        regex: "([^:]+)(:[0-9]+)?"
        replacement: "${1}"

  # Kubernetes pods with annotations
  - job_name: "kubernetes-pods"
    kubernetes_sd_configs:
      - role: pod
    relabel_configs:
      - source_labels: [__meta_kubernetes_pod_annotation_prometheus_io_scrape]
        action: keep
        regex: true
      - source_labels: [__meta_kubernetes_pod_annotation_prometheus_io_path]
        action: replace
        target_label: __metrics_path__
        regex: (.+)
      - source_labels:
          [__address__, __meta_kubernetes_pod_annotation_prometheus_io_port]
        action: replace
        regex: ([^:]+)(?::\d+)?;(\d+)
        replacement: $1:$2
        target_label: __address__
      - source_labels: [__meta_kubernetes_namespace]
        action: replace
        target_label: namespace
      - source_labels: [__meta_kubernetes_pod_name]
        action: replace
        target_label: pod

  # Application metrics
  - job_name: "my-app"
    static_configs:
      - targets:
          - "app1.example.com:9090"
          - "app2.example.com:9090"
    metrics_path: "/metrics"
    scheme: "https"
    tls_config:
      ca_file: /etc/prometheus/ca.crt
      cert_file: /etc/prometheus/client.crt
      key_file: /etc/prometheus/client.key

Reference: See assets/prometheus.yml.template

Scrape Configurations

Static Targets

scrape_configs:
  - job_name: "static-targets"
    static_configs:
      - targets: ["host1:9100", "host2:9100"]
        labels:
          env: "production"
          region: "us-west-2"

File-based Service Discovery

scrape_configs:
  - job_name: "file-sd"
    file_sd_configs:
      - files:
          - /etc/prometheus/targets/*.json
          - /etc/prometheus/targets/*.yml
        refresh_interval: 5m

targets/production.json:

[
  {
    "targets": ["app1:9090", "app2:9090"],
    "labels": {
      "env": "production",
      "service": "api"
    }
  }
]

Kubernetes Service Discovery

scrape_configs:
  - job_name: "kubernetes-services"
    kubernetes_sd_configs:
      - role: service
    relabel_configs:
      - source_labels:
          [__meta_kubernetes_service_annotation_prometheus_io_scrape]
        action: keep
        regex: true
      - source_labels:
          [__meta_kubernetes_service_annotation_prometheus_io_scheme]
        action: replace
        target_label: __scheme__
        regex: (https?)
      - source_labels: [__meta_kubernetes_service_annotation_prometheus_io_path]
        action: replace
        target_label: __metrics_path__
        regex: (.+)

Reference: See references/scrape-configs.md

Recording Rules

Create pre-computed metrics for frequently queried expressions:

# /etc/prometheus/rules/recording_rules.yml
groups:
  - name: api_metrics