Idempotency Keys: The API Pattern That Saves You From Duplicate Payments and Pha

<p>You hit "Submit Order" and nothing happens. The spinner just spins. Is it processing? Did the request get lost? You click again.</p> <p>If the API on the other end does not

<p>A scheduled post fires. The request to publish it goes out. The network hangs. After 30 seconds, our client times out. We retry. The tweet publishes. Then the original request

<p>In distributed systems, failure is not an exception—it’s the default.</p> <p>Network calls fail. Services timeout. APIs return 500s. The real question isn’t <em>“Will things

<p>Two things quietly decide whether a small application survives being used: whether its reads<br /> are indexed, and whether its writes can be repeated safely. They are usually

<p>Every payments API has an <code>Idempotency-Key</code> header. Far fewer have written down what it means, and the ones that haven't are usually running a <code>SELECT … WHERE

<h1> API layer pattern (HTTP) </h1> <h2> 1) Contract </h2> <ul> <li>Require <code>Idempotency-Key</code> on <strong>POST</strong> that creates resources (optional on GET, safe

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<p>In this guide, we explore system. Your transaction is pending. A timeout occurs. Now you're staring at a screen wondering if you just paid $1,000 twice or if your money