Swarm Service Autoscaler

Links

• Docker hub

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Description

The project is an application that implements the ability to dynamically change the number of service instances under high load. The application receives all services that have the swarm.autoscale label enabled, calculates the average value of the CPU utilization and, based on this, either increases the number of instances or decreases it.

Currently, only the CPU is used for autoscaling in the project. By default, if the CPU load reaches 85%, the service will scale, if it reaches 25%, it will be scaled down. But the minimum and maximum values ​​of CPU utilization can be changed through environment variables.

Also, for each service, you can set the maximum and minimum number of replicas to prevent a situation with an uncontrolled increase in the number of replicas (or too much decrease)

Usage

1. Deploy Swarm Autoscaler using swarm-deploy.yml from this repository
2. Add label swarm.autoscale=true for services you want to autoscale.

deploy:
  labels:
    - "swarm.autoscale=true"

For better resource management, it is recommended to add resource constraints to your service. Then it will definitely not eat more resources than necessary, and auto-scaling will work much better and will save resources in idle time.

deploy:
  resources:
    limits:
      cpus: '0.50'

Configuration

Swarm Autoscaler configuration

The application is configured through environment variables

Setting	Default Value	Description
AUTOSCALER_MIN_PERCENTAGE	25	minimum service cpu utilization value in percent (0-100) for decrease replicas
AUTOSCALER_MAX_PERCENTAGE	85	maximum service cpu utilization value in percent (0-100) for increase replicas
AUTOSCALER_DNSNAME	tasks.autoscaler	swarm service name for in stack communication
AUTOSCALER_INTERVAL	300	interval between checks in seconds
AUTOSCALER_DRYRUN	false	noop mode for check service functional without enable inc or dec service replicas count

Services configuration

Services in docker swarm are configured via labels

Setting	Value	Default	Description
swarm.autoscale	Boolean	false	Required. This enables autoscaling for a service. Anything other than true will not enable it
swarm.autoscale.min	Integer	2	Optional. This is the minimum number of replicas wanted for a service. The autoscaler will not downscale below this number
swarm.autoscale.max	Integer	15	Optional. This is the maximum number of replicas wanted for a service. The autoscaler will not scale up past this number
swarm.autoscale.disable-manual-replicas	Boolean	false	Optional. Disable manual control of replicas. It will no longer be possible to manually set the number of replicas more or less than the limit. Anything other than true will not enable
swarm.autoscale.percentage-max	Integer	AUTOSCALER_MAX_PERCENTAGE	Optional. Custom maximum service cpu utilization for increase replicas
swarm.autoscale.percentage-min	Integer	AUTOSCALER_MIN_PERCENTAGE	Optional. Custom minimum service cpu utilization for decrease replicas
swarm.autoscale.decrease-mode	String	MEDIAN	Optional. Service utilization calculation mode to decrease replicas. Modes: MEDIAN, MAX