Observers

Observer configuration controls retry behavior, timeouts, watchdog monitoring, and how events fan out to scaled-out client instances.

Example configuration

{
  "observers": {
    "subscriberTimeout": 5,
    "maxRetryAttempts": 10,
    "backoffDelay": 1,
    "exponentialBackoffDelayFactor": 2,
    "maximumBackoffDelay": 600,
    "watchdogInterval": 60,
    "fanOutStrategy": "round-robin"
  }
}

Property	Type	Default	Description
subscriberTimeout	number	5	Timeout in seconds for observer subscriber calls
maxRetryAttempts	number	10	Maximum retry attempts for failed partitions (0 = infinite)
backoffDelay	number	1	Initial backoff delay in seconds
exponentialBackoffDelayFactor	number	2	Exponential backoff multiplier
maximumBackoffDelay	number	600	Maximum backoff delay in seconds
watchdogInterval	number	60	Interval in seconds between watchdog checks; the watchdog verifies connected clients are still active, running jobs (replay and catch-up) are still progressing, and NextEventSequenceNumber is up-to-date
fanOutStrategy	string	round-robin	Strategy for distributing events across multiple connected instances of the same client. round-robin distributes deterministically by partition key, keeping every partition sticky to one instance and preserving per-partition ordering. random picks a random instance per delivery

Scaled-out clients

When multiple instances of the same client application connect, its reactors and reducers all subscribe to the same observer. Chronicle fans event delivery out across the instances using the configured fanOutStrategy. If an instance disconnects, it is removed immediately and its partitions are redistributed to the remaining instances - the observer only unsubscribes when the last instance is gone.