Delivery policy

Each URL destination has a delivery policy: how long to wait for an answer, which answers are worth retrying, how long to wait between tries, and how fast to send. Defaults are sensible; change them when your service has its own limits.

What counts as a failure

Ensue retries answers that might succeed later, and fails fast on ones that never will.

Response	Result
2xx	Delivered.
408, 409, 425, 429, 5xx, timeout, network error	Retried.
Other 4xx (for example 400, 401, 404, 422)	Failed at once. Your service rejected the request; trying again would not help.
3xx	Failed. Redirects are never followed.
Retry-After: -1 or x-ensue-retry: never	Failed at once, on any non-2xx answer. Your service can say “never retry this”.

Change which answers retry with retry.retry_on, an array drawn from 5xx, 429, 408, 409, 425, timeout and network, or a specific status code.

Retries and backoff

By default a failed delivery is retried up to 7 times, after 5 seconds, 30 seconds, 2 minutes, 10 minutes, 1 hour, 2 hours and 4 hours. That is eight attempts across about seven hours. Each wait is spread randomly by up to half in either direction so retries from many events don’t land together.

{
  "max_attempts": 12,
  "retry": { "schedule": "exponential", "interval_seconds": 30, "max_window_hours": 24 }
}

Setting	Meaning
max_attempts	Total attempts before the event becomes a dead letter.
retry.schedule	default (the schedule above), linear (the same wait every time) or exponential (doubling from interval_seconds, capped at one day).
retry.interval_seconds	The base wait for linear and exponential.
retry.max_window_hours	A cut-off after which an event stops retrying, whatever attempts remain.
retry.retry_on	Which responses retry.

Retry-After

If your service answers 429 or 503 with a Retry-After header, in seconds or as an HTTP date, Ensue honours it, up to four hours. The header can only push a retry later, never earlier.

Timeouts

timeout_ms is how long Ensue waits for an answer: 1,000 to 30,000 milliseconds, default 15,000. If your handler needs longer, accept the event quickly and process it in the background, or use a deferred acknowledgement.

Rate and concurrency

Setting	Meaning
max_in_flight	The most deliveries running at once.
rate_per_second with rate_period	The most deliveries started in each second, minute or hour.

Events queue in Ensue and drain at the rate you set instead of failing and retrying against a downstream limit. For per-tenant fairness, use delivery groups.

Pausing a destination

Pausing holds every event for that destination until you resume. Nothing is lost, and nothing is retried while paused.

Manual retries

Any event can be retried by hand, even after it has given up. A manual retry sends one attempt immediately and is not counted against the schedule. See Replay and dead letters.