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Since we’ve decided to go with Option 2 and Option 4, and to implement a circuit breaker pattern, the main focus of the technical delivery will be on how to integrate this into the mod_scheduler service and what approaches we should use. For the future, we have also decided to create a dashboard that can display timers along with their statuses. To achieve this, we will introduce timer statuses in the first iteration of implementation, which the UI will then use to display them on the dashboard.

Own imllementation

Firstly, I think we don't need to introduce a new framework to handle the circuit breaker pattern; we should try to implement it using the existing Quartz framework. Since Quartz is already established for the service and supports distributed job handling, the idea is to pause the timer job each time it fails and create a circuit breaker job, which will be scheduled to execute based on the number of timer failures. We will store the number of failures for the timer job in the timer descriptor, along with the timer statuses.

Hystrix

The most popular circuit breaker pattern library, built by Netflix, is Hystrix. The implementation will be straightforward: we'll wrap our call to the timer endpoint with a HystrixCommand, running asynchronously and managing all statuses if the call fails. Each HystrixCommand should have a unique key, which should match the timer job key.

pros

popular and easy implementation

cons

"multi instances" implementation - each node has completely separate circuit breakers and there's no shared data between nodes

resilience4j

Another popular library that implements the circuit breaker pattern provides a circuit breaker registry, allowing us to register our circuit breakers. It can be customized to use not only in-memory storage but also shared services like an in-memory database or a traditional database.

Pros:

• Easy to implement

• The registry can be shared across instances

cons

Extend Time Descriptor to add two new properties: failed status and failure count

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "title": "TimerDescriptor",
  "description": "Timer",
  "type": "object",
  "properties": {
    "id": {
      "description": "Timer identifier",
      "type": "string",
      "format": "uuid"
    },
    "modified": {
      "description": "Whether modified",
      "type": "boolean"
    },
    "routingEntry": {
      "$ref": "routingEntry.json",
      "description": "Proxy routing entry"
    },
    "enabled": {
      "description": "Whether enabled",
      "type": "boolean"
    },
    "moduleName": {
      "description": "Module name timer belongs to",
      "type": "string"
    },
    "failedlastFailedDate": {
      "description": "DidThe date of the last execution failfailure.",
      "type": "boolean"
    },
    "failureCount": {
      "description": "Failure count",
      "type": "integer"
    }
  },
  "required": [ "routingEntry", "enabled" ]
}

Each time the timer fails, we will increment the failure count by 1, and if it runs successfully, we will reset the count to 0. This value will determine when to schedule the circuit breaker job to resume the timer. To schedule the circuit breaker job, we will use a SimpleTrigger that fires at a specific time without repeating.

For each circer bbrecer job we add We add a job data item which include for each circuit breaker job that includes the timer job key to be able to resume itallow it to be resumed. No additional interaction with databse not the database is required. Once the circle job expected circuit breaker job has been triggered at least once, it should be deleted.

An additional REST endpoint needs to be added to the scheduler module to allow manual resumption of timers. This will enable the operations team to monitor timers via the dashboard, identify and resolve issues that caused failures, and resume the timers immediately, without waiting for the circuit breaker job to resume them in the next cycle.

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