A time series database, for storing and serving metrics.

Basics

  • Prometheus runs on port 9090 by default.

Getting started

Deploying on OpenShift 3.x

Deploying a wee Prometheus on OpenShift 3.11:

oc process -f https://raw.githubusercontent.com/openshift/origin/release-3.11/examples/prometheus/prometheus-standalone.yaml

oc create -f - <<HELLO
apiVersion: v1
kind: Secret
metadata:
  name: prom
stringData:
  prometheus.yml: |
    global:
      scrape_interval:     15s # Set the scrape interval to every 15 seconds. Default is every 1 minute.
      evaluation_interval: 15s # Evaluate rules every 15 seconds. The default is every 1 minute.
      # scrape_timeout is set to the global default (10s).

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

    # A scrape configuration containing exactly one endpoint to scrape:
    # Here it's Prometheus itself.
    scrape_configs:
      # The job name is added as a label `job=` to any timeseries scraped from this config.
      - job_name: 'prometheus'

        # metrics_path defaults to '/metrics'
        # scheme defaults to 'http'.

        static_configs:
        - targets: ['localhost:9090']

      # Scrape configuration for our hello world app
      - job_name: 'myapp'
        static_configs:
        - targets: ['myapp:8080']
HELLO

oc create -f - <<HELLO
apiVersion: v1
kind: Secret
metadata:
  name: prom-alerts
stringData:
  alertmanager.yml: |
    global:
    # The root route on which each incoming alert enters.
    route:
      # default route if none match
      receiver: alert-buffer-wh
    receivers:
    - name: alert-buffer-wh
      webhook_configs:
      - url: http://localhost:9099/topics/alerts
HELLO

Scraping metrics

Listing metrics from an existing app

If you’re running an application which already exposes metrics for Prometheus, and you want to see which metrics are exposed.

For example, for Loki which runs on port 3100:

# 
kubectl port-forward loki-pod-name 3101:3100

# Then fetch the metrics endpoint - usually at /metrics
curl localhost:3101/metrics

Cookbook

Rates

  • Use irate for volatile, fast-moving counters
  • Use rate for alerts and slow-moving counters

From a counter of HTTP requests, get the per-second rate of HTTP requests, measured over the last 5 minutes:

rate(http_requests_total{job="api-server"}[5m])

Alert queries

Predict a node’s free disk space in X hours

predict_linear(node_filesystem_avail_bytes{job="node"}[1h], 8 * 3600) < 0
  • Get 1 hour’s worth of node_filesystem_avail_bytes history
  • Use predict_linear to predict 8 hours ahead (8 x 3600)
  • Test whether the value will be less than 0 - i.e. no free disk space

Source

Targets

Kubernetes

Prometheus uses Kubernetes Service Discovery (SD) to be able to scrape targets using the Kubernetes REST API.

  1. Set up a job in Prometheus which uses Kubernetes Service Discovery. e.g. this configuration fragment from a sample prometheus.yml:
  - job_name: 'kubernetes-service-endpoints'

  kubernetes_sd_configs:
  - role: endpoints
  1. Add the following annotations (not Labels!) to the Service in Kubernetes that you want to be scraped:
prometheus.io/scrape: "true"
prometheus.io/path: "/metrics"
prometheus.io/port: "8672"