Trigger Failure Strategy

This repo has a simple example of a way to handle triggers that get in a loop constantly retrying a failed command.

When the trigger reaches its maximum amount of failures, a TriggerFailureNotification contract is created that includes the failure messages that accumulated during the triggers last run. The party running the trigger then has the opportunity to exercise the StartTrigger choice which will reset the amount of failures and let the trigger restart.

To test this out, build both the trigger dar and model dar (make build will place them in target) and upload them to Daml Hub (or the example can be run locally).

Start a trigger as Alice, and then create an AssetOrArchive contract with fail set to true. When the trigger fails 10 times, it will pause and create the notification contract, on which the StartTrigger choice can be exercised and the trigger will start again.

To use this code in your own project:

1. Include TriggerFailureNotification and FailedTriggerStartRequest from daml/Main.daml in your model
2. Include FailureState, updateStateFailures and withFailures from triggers/daml/Trigger.daml in your trigger's Daml code
3. Use updateStateFailure as the updateState function in your Trigger settings function. If you have a custom updateState function, you will need to call updateStateFailures in it.
4. In your initialize function, use initFailureState with the number of possible retries
5. Use FailureState as the trigger's state (e.g. T.Trigger FailureState)
6. Wrap all code in your trigger rule in withFailures as seen below.

Example:

trigger : T.Trigger FailureState
trigger = T.Trigger
  { initialize = pure $ initFailureState 10
  , updateState = updateStateFailures
  , rule = triggerRule
  , registeredTemplates = T.AllInDar
  , heartbeat = None
  }

triggerRule : Party -> T.TriggerA FailureState ()
triggerRule party = withFailures party $ do
      -- trigger code here as normal
      return ()

If you are already using a custom state in your trigger, you will have to include FailureState in it and modify updateStateFailures, initTriggerState and withFailures accordingly.

Sample code

This repo contains sample code to help you get started with DAml. Please bear in mind that it is provided for illustrative purposes only, and as such may not be production quality and/or may not fit your use-cases. You may use the contents of this repo in parts or in whole according to the BSD0 license:

Copyright © 2022 Digital Asset (Switzerland) GmbH and/or its affiliates

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.