Dark Knight

The Dark Knight automatically restarts your Heroku dynos if they start swapping to disk R14 - Memory Quota Exceeded in Ruby (MRI).

Once a Heroku dyno starts swapping to disk, it becomes comparatively slow and unresponsive, so taking it out of the formation is the best course of action.

He's a silent guardian, a watchful protector. A dark knight.

~ Jonathan Nolan, The Dark Knight

Setup

Deploying the Dark Knight

To deploy the service:

$ git clone https://github.com/karlentwistle/dark_knight.git
$ heroku create <your_dark_knight_app_name>
$ heroku buildpacks:add heroku/ruby
$ heroku config:set APP_ID_OR_NAME=<ID_OR_NAME_OF_HEROKU_APP_BEING_MONITORED>
$ heroku config:set DRAIN_PASSWORD=<YOUR_DRAIN_PASSWORD>
$ heroku config:set AUTH_TOKEN=<HEROKU_API_AUTHENTICATION_TOKEN>
$ heroku config:set DYNO_TYPES=web,worker
$ heroku config:set RACK_ENV=production
$ git push heroku main

Instrumenting an App

To instrument an app:

$ heroku labs:enable log-runtime-metrics --app <ID_OR_NAME_OF_HEROKU_APP_BEING_MONITORED>
$ heroku drains:add https://user:<YOUR_DRAIN_PASSWORD>@<YOUR_DARK_KNIGHT_APP>.herokuapp.com/logs --app <ID_OR_NAME_OF_HEROKU_APP_BEING_MONITORED>

Configuration

The following is the full list of ENV configuration options:

ENV name	Description	Example	Default	Required
DRAIN_PASSWORD	HTTPS drain password	DRAIN_PASSWORD=password	N/A	✅
APP_ID_OR_NAME	ID or name of Heroku app being monitored	APP_ID_OR_NAME=whatismyip	N/A	✅
AUTH_TOKEN	Heroku API authentication token	AUTH_TOKEN=cf0e05d9-4eca-4948-a012-b91fe9704bab	N/A	✅
DYNO_TYPES	Dynos to restart when swapping (R14) or over specified threshold	DYNO_TYPES=web,worker	web	❌
{DYNO_TYPE}_RESTART_THRESHOLD	Threshold in megabytes for specific dyno type to restart if breached	WEB_RESTART_THRESHOLD=1024	Dyno memory quota	❌
{DYNO_TYPE}_RESTART_WINDOW	Restart rate limit in seconds for specific dyno type	WEB_RESTART_WINDOW=300	10 minutes (600)	❌
SLACK_WEBHOOK_URL	Slack messages webhook URL	SLACK_WEBHOOK_URL=https://hooks.slack.com/services/top/secret/password	N/A	❌