The Heroku Reactions are designed to allow users to automatically perform common tasks for Heroku applications. Common tasks include scaling, restarting dynos and rolling back application versions.
Scale Out Dynos
The Scale Out Dynos Reaction will increase the defined dynos by 1 every time it is triggered. If this Reaction is attached to a Monitor that runs at a 30 second interval, the Reaction will increase the number of dynos by one until the Monitor changes state to one that does not match the Call On field.
This Reaction will not scale beyond the Maximum Dyno Quantity. Once this value is reached the Reaction will stop executing.
Scale In Dynos
The Scale In Dynos Reaction will decrease the defined dynos by 1 every time it is triggered. If this Reaction is attached to a Monitor that runs at a 30 second interval, the Reaction will decrease the number of dynos by one until the Monitor changes state to one that does not match the Call On field.
This Reaction will not scale below the Minimum Dyno Quantity. Once this value is reached the Reaction will stop executing.
Scale Up Dynos
The Scale Up Dynos Reaction will increase the size of the defined dyno/s every time it is triggered. If a dyno is currently 1X size, it will be scaled to 2X on the next invocation of this Reaction and to PX on the third.
This Reaction will not scale beyond the Maximum Dyno Size defined for the Reaction.
Scale Down Dynos
The Scale Down Dynos Reaction will decrease the size of the defined dyno/s every time it is triggered. If a dyno is currently PX size, it will be scaled to 2X on the next invocation of this Reaction and to 1X on the third.
This Reaction will not scale below the Minimum Dyno Size defined for the Reaction.
Restart Single Dyno
When triggered, the Restart Single Dyno Reaction will make a call to the Heroku Platform API to restart the specific dyno. This Reaction is a simple restart of one specific dyno.
Restart All Dynos
When triggered, the Restart All Dynos Reaction will make a call to the Heroku Platform API to restart all dynos associated with the specified application.
Rollback Release
When triggered, the Rollback Release Reaction will make a call to the Heroku Platform API to rollback the applications release by 1 version. This Reaction will continue rolling back the application version until the triggering Monitor is returned to it's desired state or the current version matches the Minimum Release Version defined in the Reaction.
Create One-Off Dyno
One-off dynos in Heroku are generally used to kick off maintenance scripts or other back-end jobs. These dynos typically run a process until it stops and then they are complete. The Create One-Off Dyno Reaction allows users to spawn a one off dyno and specify any command they want to run.
A real world example of this Reaction would be detecting a database error using the HTTP GET: Keyword and launching a Create One-Off Dyno Reaction to run a clean up script.