A Ruby gem to monitor docker swarm mode services and auto-scale them based on user configuration. It can be used to monitor web services and worker services. The web services type has metrics like response time using New Relic. The worker services type metrics are basically the queue size for each. This gem is inspired by HireFire and was indeed motivated by the migration from Heroku to Docker Swarm mode.

Add this line to your application's Gemfile:

gem 'scaltainer'

And then execute:

$ bundle

Or install it yourself as:

$ gem install scaltainer

scaltainer

This will do a one-time check on the running service replicas and sends scaling out/in commands to the swarm cluster as appropriate. Configuration is read from scaltainer.yml by default. If you want to read from another file add -f yourconfig.yml:

scaltainer -f yourconfig.yml

Note that after each run a new file is created (yourconfig.yml.state) which stores the state of the previous run. This is because there are some configuration parameters (like sensitivity) need to remember previous runs. If you want to specify a different location for the state file, add the --state-file parameter. Example:

scaltainer -f /path/to/configuration/file.yml --state-file /path/to/different/state/file.yml

Typically, the above command should be put inside a cronjob that is triggered every minute or so.

• DOCKER_URL: Should point to the docker engine URL. If not set, it defaults to local unix socket.

• HIREFIRE_TOKEN: If your application is configured the hirefire way, you need to set HIREFIRE_TOKEN environment variable before invoking scaltainer. This is used when probing your application endpoint (see below) to get the number of jobs per queue for each worker.

• NEW_RELIC_API_KEY: New Relic API key. Currently New Relic is used to retrieve average response time metric for web services. More monitoring services can be added in the future.

• RESPONSE_TIME_WINDOW: Time window in minutes to measure average response time till the moment. For example 3 means measure average response time in the past 3 minutes. Default value is 5.

• LOG_LEVEL: Accepted values here are: DEBUG, INFO (default), WARN, ERROR, FATAL. Log output goes to stdout.

• DOCKER_SECRETS_PATH_GLOB: Path glob containing environment files to load. This is useful if running from a docker swarm mode environment where one or more of the above environment variables are set using docker config or docker secret. These files should be in the form VARIABLE=value. A typical value of this variable would be: {/run/secrets/*,/config1,/config2}

The configuration file (determined by -f FILE command line parameter) should be in the following form:

# to get worker metrics
endpoint: https://your-app.com/hirefire/$HIREFIRE_TOKEN/info
# optional docker swarm stack name
stack_name: mystack
# list of web services to monitor
web_services:
  # each service name should match docker service name
  web:
    # New Relic application id (required)
    newrelic_app_id: <app_id>
    # minimum replicas to maintain (default: 0)
    min: 1
    # maximum replicas to maintain (default: unlimited)
    max: 5
    # maximum response time above which to scale up (required)
    max_response_time: 300
    # minimum response time below which to scale down (required)
    min_response_time: 100
    # replica quantitiy to scale up at a time (default: 1)
    upscale_quantity: 2
    # replica quantitiy to scale down at a time (default: 1)
    downscale_quantity: 1
    # number of breaches to wait for before scaling up (default: 1)
    upscale_sensitivity: 1
    # number of breaches to wait for before scaling down (default: 1)
    downscale_sensitivity: 1
  webapi:
    ...
worker_services:
  worker1:
    min: 1
    max: 10
    # number of jobs each worker replica should process (required)
    # the bigger the ratio, the less number of workers scaled out
    ratio: 3
    upscale_sensitivity: 1
    downscale_sensitivity: 1
  worker2:
    ...

More details about configuration parameters can be found in HireFire docs.

After checking out the repo, run bin/setup to install dependencies. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/hammady/scaltainer.

• Rspec

The gem is available as open source under the terms of the MIT License.