Docker Scaler

Microservice providing a REST API that scales services in Docker Swarm.

Usage

Consider the services defined by the following compose spec:

version: "3.3"

services:
  scaler:
    image: thomasjpfan/docker-scaler:latest
    environment:
      - ALERTMANAGER_ADDRESS=http://alertmanager:9093
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    ports:
      - 8080:8080
    deploy:
      placement:
        constraints: [node.role == manager]
  web:
    image: alpine:3.6
    deploy:
      replicas: 3
      labels:
        com.df.scaleMin: "2"
        com.df.scaleMax: "4"
    command: sleep 10000000
  alertmanager:
    image: prom/alertmanager:v0.8.0
    ports:
      - 9093:9093

The web service represents a long running process that can be scaled. The labels com.df.scaleMin and com.df.scaleMax represents the minimum and maximum number of replicas for the web service.

Example

Deploying script/docker-scaler-readme.yml as a stack:

$ docker stack deploy -c scripts/docker-scaler-readme.yml example

Following the naming convention of docker stack deploy, this will create three services example_scaler, example_web, example_alertmanager. Port 8080 exposes the example_scaler service and port 9093 exposes example_alertmanager to your local machine. To scale example_web up by one replica send the following request:

$ curl -X POST localhost:8080/v1/scale-service?name=example_web&delta=1

This will also send an alert to the alertmanager, you can query the alertmanager by installing amtool and running:

$ amtool --alertmanager.url http://localhost:9093 alert

This will list the alerts received by the alertmanager:

Alertname      Starts At                Summary
scale_service  2017-09-25 16:44:12 UTC  Scaling example_web to 4 replicas

To scale example_web down by one, send the following request:

$ curl -X POST localhost:8080/v1/scale-service?name=example_web&delta=-1

Running the amtool query again will display:

Alertname      Starts At                Summary
scale_service  2017-09-25 16:55:01 UTC  Scaling example_web to 3 replicas

If you wish to display all the information in an alert run:

$ amtool --alertmanager.url http://localhost:9093 -o extended alert

AWS Integration

Create secret for AWS access

echo 'export AWS_ACCESS_KEY_ID=xxxx
export AWS_SECRET_ACCESS_KEY=xxxx
' | docker secret create aws -

In scripts/docker-scaler-aws.yml, overwrite AWS_MANAGER_GROUP_NAME and AWS_WORKER_GROUP_NAME with your autoscaling group names. Then deploy it as a stack:

$ docker stack deploy -c scripts/docker-scaler-aws.yml aws

To send request to scale up worker node:

$ curl -X POST [PUBLIC_DNS]:8080/v1/scale-nodes?backend=aws&delta=1&type=worker

Or scaling up a manager node:

$ curl -X POST [PUBLIC_DNS]:8080/v1/scale-nodes?backend=aws&delta=1&type=manager