Source: wshobson/agents Original Plugin: observability-monitoring

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

BASH

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

YAML

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:

YAML

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

YAML

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

File-based Service Discovery

YAML

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

targets/production.json:

JSON

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

Kubernetes Service Discovery

YAML

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:

YAML

# /etc/prometheus/rules/recording_rules.yml
groups:
  - name: api_metrics
    interval: 15s
    rules:
      # HTTP request rate per service
      - record: job:http_requests:rate5m
        expr: sum by (job) (rate(http_requests_total[5m]))

      # Error rate percentage
      - record: job:http_requests_errors:rate5m
        expr: sum by (job) (rate(http_requests_total{status=~"5.."}[5m]))

      - record: job:http_requests_error_rate:percentage
        expr: |
          (job:http_requests_errors:rate5m / job:http_requests:rate5m) * 100

      # P95 latency
      - record: job:http_request_duration:p95
        expr: |
          histogram_quantile(0.95,
            sum by (job, le) (rate(http_request_duration_seconds_bucket[5m]))
          )

  - name: resource_metrics
    interval: 30s
    rules:
      # CPU utilization percentage
      - record: instance:node_cpu:utilization
        expr: |
          100 - (avg by (instance) (rate(node_cpu_seconds_total{mode="idle"}[5m])) * 100)

      # Memory utilization percentage
      - record: instance:node_memory:utilization
        expr: |
          100 - ((node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes) * 100)

      # Disk usage percentage
      - record: instance:node_disk:utilization
        expr: |
          100 - ((node_filesystem_avail_bytes / node_filesystem_size_bytes) * 100)

Reference: See references/recording-rules.md

Alert Rules

YAML

# /etc/prometheus/rules/alert_rules.yml
groups:
  - name: availability
    interval: 30s
    rules:
      - alert: ServiceDown
        expr: up{job="my-app"} == 0
        for: 1m
        labels:
          severity: critical
        annotations:
          summary: "Service {{ $labels.instance }} is down"
          description: "{{ $labels.job }} has been down for more than 1 minute"

      - alert: HighErrorRate
        expr: job:http_requests_error_rate:percentage > 5
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "High error rate for {{ $labels.job }}"
          description: "Error rate is {{ $value }}% (threshold: 5%)"

      - alert: HighLatency
        expr: job:http_request_duration:p95 > 1
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "High latency for {{ $labels.job }}"
          description: "P95 latency is {{ $value }}s (threshold: 1s)"

  - name: resources
    interval: 1m
    rules:
      - alert: HighCPUUsage
        expr: instance:node_cpu:utilization > 80
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "High CPU usage on {{ $labels.instance }}"
          description: "CPU usage is {{ $value }}%"

      - alert: HighMemoryUsage
        expr: instance:node_memory:utilization > 85
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "High memory usage on {{ $labels.instance }}"
          description: "Memory usage is {{ $value }}%"

      - alert: DiskSpaceLow
        expr: instance:node_disk:utilization > 90
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: "Low disk space on {{ $labels.instance }}"
          description: "Disk usage is {{ $value }}%"

Validation

BASH

# Validate configuration
promtool check config prometheus.yml

# Validate rules
promtool check rules /etc/prometheus/rules/*.yml

# Test query
promtool query instant http://localhost:9090 'up'

Reference: See scripts/validate-prometheus.sh

Best Practices

Use consistent naming for metrics (prefix_name_unit)
Set appropriate scrape intervals (15-60s typical)
Use recording rules for expensive queries
Implement high availability (multiple Prometheus instances)
Configure retention based on storage capacity
Use relabeling for metric cleanup
Monitor Prometheus itself
Implement federation for large deployments
Use Thanos/Cortex for long-term storage
Document custom metrics

Troubleshooting

Check scrape targets:

BASH

curl http://localhost:9090/api/v1/targets

Check configuration:

BASH

curl http://localhost:9090/api/v1/status/config

Test query:

BASH

curl 'http://localhost:9090/api/v1/query?query=up'

Reference Files

assets/prometheus.yml.template - Complete configuration template
references/scrape-configs.md - Scrape configuration patterns
references/recording-rules.md - Recording rule examples
scripts/validate-prometheus.sh - Validation script

grafana-dashboards - For visualization
slo-implementation - For SLO monitoring
distributed-tracing - For request tracing