Dynamically scale docker swarm services using the number of unacknowledged messages from an AMQP queue like RabbitMQ. This is useful if you use AMQP as a job queue and the number of messages indicates the load on your system.

go get github.com/sprungknoedl/kogia

kogia is configured using a YAML configuration file. Below is an example configuration for the docker swarm service helloworld:

connection:
  amqp: amqp://localhost:5672/
  docker: unix:///run/docker.sock
defaults:
  sample_rate: 2s
  scale_rate: 30s
  upscale_delay: 3m
  downscale_delay: 5m
  coverage: .75
services:
  - service: helloworld
    metrics: 
    - queue.helloworld
    threshold: 10
    min_replicas: 1
    max_replicas: 10

kogia can scale multiple docker swarm services at once, all with different scale intervals and delays.

Each service has the following configuration parameters. If the parameter is not provided for a service, the default value specified in the configuration will be used. kogia doesn't provide any internal defaults!

• service: name of the docker swarm service to scale.
• metrics: list of names of the AMQP queues used as load indicator.
• coverage: percentage of metrics required to calculate average queue length (recommended: 0.75).
• threshold: number of messages on a queue representing maximum load of one service replica.
• min_replicas: minimum number of replicas for this service. kogia will never scale the service below this number. It is safe to specify 0; as soon as some message are queued, kogia will scale the replicas to 1.
• max_replicas: maximum number of replicas for this service. kogia will never scale the service above this number.
• sample_rate: time interval between measurements of the metric (recommended: 2s).
• scale_rate: time interval between autoscaling calculations. Must be a multiple of sample_rate (recommended: 30s).
• upscale_delay: minimum time between the last rescaling and the next upscaling (recommended: 3m).
• downscale_delay: minimum time between the last rescaling and the next downscaling. The downscale_delay should be higher than the upscale_delay to prevent flapping (recommended: 5m).