Every payment API has it, and almost no internal service does. Idempotency keys are the cheapest way to make a queue safe. The shape I use in Go: The subtle parts: store the response, not just the status; set the…
Imagine you are ordering food online. You tap “Place Order.” The app starts processing your order, but the internet connection suddenly drops. You don't know whether the order was placed successfully. So, you tap the button again. A few seconds…
Engineers file idempotency under plumbing: a key, a dedupe check, a thing the framework mostly handles. Merchants experience it as something else entirely — the difference between a recovery tool and a liability. Retry a card twice by accident and you…
You send a request that triggers an e-mail, a push notification, an SMS or a payment. The connection drops. You do not know whether the server received it. Do you send it again? If you retry, you may send the…
TL;DR: Put a four-state incident ledger between the poller and the webhook sender: healthy, firing, cooldown, and recovering. Key it by the pricing rule and normalized failure condition, reserve a notification before sending, and require consecutive healthy polls before…
Idempotency. Eight letters, five syllables, and a word I pretended to understand in meetings for an embarrassingly long time. So today we are going to build the bug that makes idempotency matter, charge a fake customer twice, and then fix…
Every payment integration eventually ships the same bug. A client sends POST /charge, the request succeeds, the response times out in transit, the client retries, and the customer is billed twice. Nobody wrote incorrect logic. The bug lives in the…
You click Pay. The server charges your card, but the response is lost on the way back (network drop, timeout, tab freeze). The UI thinks it failed, so you click Pay again and get charged twice. A timeout means "I…
Imagine you are designing a system like Amazon, Instagram, or Uber. At first, this sounds simple. But what happens when your application runs across 100 servers in multiple regions, processes millions of requests per second, and must continue working even when…
Circuit breakers, retries/backoff, bulkheads, and caching strategies.
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