Idempotency Keys in Spring Boot: Make POST Safe Against Retries

<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>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><em>Originally published on <a href="https://loopandretry.github.io/posts/what-idempotent-means/?ref=devto" rel="noopener noreferrer">Loop &amp; Retry</a> — field notes on

<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

<h1> Idempotency Keys: The API Pattern That Saves You From Duplicate Payments and Phantom Records </h1> <p>Your user clicks "Pay" and nothing happens. So they click again. Your

<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>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

<p>Duplicate processing is one of those integration problems that looks small in development but becomes painful in production.</p> <p>A client retries an API call because the