joeelliott/kubernetes-prometheus-scaler repository overview

⁠kubernetes-prometheus-autoscaler

Scale deployments based on prometheus queries

⁠How to use

Run this as a pod in your cluster. The container image⁠ is available on DockerHub.

Add this label to deployments you want considered for scaling:

  labels:
    scale: prometheus

There are three different scaling strategies currently available. See below for the annotations necessary to control scaling.

⁠Step Scaling

With step scaling you provide a query and two conditions. The two conditions scale-up-when and scale-down-when are evaluated to determine whether or not the deployment should be scaled up or down by 1 replica.

    prometheusScaler/prometheus-query: "time() % 60"
    prometheusScaler/min-scale: "2"
    prometheusScaler/max-scale: "5"
    prometheusScaler/scale-up-when: "result > 50"
    prometheusScaler/scale-down-when: "result < 10"

⁠Direct Scaling

With direct scaling you provide a query and one condition. The replica count is set to the value retrieved from evaluating the scale-to expression directly.

    prometheusScaler/prometheus-query: "time() % 60"
    prometheusScaler/min-scale: "2"
    prometheusScaler/max-scale: "5"
    prometheusScaler/scale-to: "result"

⁠Relative Scaling

With relative scaling you provide a query and one condition. The replica count is set to the value retrieved from evaluating the scale-relative expression and adding it to the current number of replicas.

    prometheusScaler/prometheus-query: "time() % 3 - 1"
    prometheusScaler/min-scale: "2"
    prometheusScaler/max-scale: "5"
    prometheusScaler/scale-relative: "result"

Scale up, scale down, scale relative and scale to conditions use this clever repo https://github.com/Knetic/govaluate⁠. The value retrieved from the query is exposed to the expression as a parameter named result.

⁠Command Line Usage

  -assessment-interval duration
        Time to sleep between checking deployments. (default 1m0s)
  -prometheus-url string
        URL to query. (default "http://prometheus:9090")

⁠Prometheus Metrics

Publishes prometheusscaler_error_total on port 8080 at /metrics. You can use this to alert on exceptions thrown while executing queries or attempting to scale.

⁠Improvements

This repo is still under active development and needs a long list of improvements. Some obvious ones:

• Better logging
• Obvious Performance Improvements (Don't run scale up query if at max)
• Comments/documentation
• Publish to docker hub once it sucks less
• Refactor to use go funcs and channels?
• Add more scaling strategies?
• Add more testing