--- title: Day 18/30 — Make It Idempotent | daily.dev description: Systems that handle retries, webhooks, and queue redelivery must treat duplicate operations as normal rather than exceptional. Key protections discussed... canonical: https://daily.dev/posts/day-18-30-make-it-idempotent-ifvtwniu1 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Day 18/30 — Make It Idempotent | daily.dev og:description: Systems that handle retries, webhooks, and queue redelivery must treat duplicate operations as normal rather than exceptional. Key protections discussed... og:url: https://daily.dev/posts/day-18-30-make-it-idempotent-ifvtwniu1 og:image: https://api.daily.dev/og/posts/ifvtwniu1.png og:image:alt: Day 18/30 — Make It Idempotent og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Day 18/30 — Make It Idempotent **[Nestjs Developers](https://daily.dev/sources/nestjsdevs)** · [@ezilemdodana](https://daily.dev/ezilemdodana) · 1 min read · 7 upvotes · 1 comments ## Summary Systems that handle retries, webhooks, and queue redelivery must treat duplicate operations as normal rather than exceptional. Key protections discussed include idempotency keys, unique database constraints, atomic state transitions, stored provider references, and idempotent job processors. A simple check-then-insert pattern is insufficient under race conditions, since 'exactly once' delivery is a promise, while true idempotent processing is what engineers must actually build. ## Content Clients retry. Payment gateways resend webhooks. Queues redeliver jobs. Your system must assume that the same operation can arrive more than once. Useful protections include: - Idempotency keys - Unique database constraints - Atomic state transitions - Stored provider references - Idempotent job processors Checking whether a record exists and then inserting it is not enough when two requests race. “Exactly once” is usually a promise. Idempotent processing is the engineering. Which endpoint in your application most needs an idempotency key? #NestJS #DistributedSystems #Payments ## Community discussion Top comments from developers on daily.dev. **@navyaak** · 1 upvotes > Payment-related endpoints most need idempotency keys.Duplicate requests should be prevented from causing multiple charges or transactions. But system should capable of identifying duplicate or requests with same details. So cannot use the request details alone to detect duplicates. ## Similar posts on daily.dev - [How to Stop Charging Customers Twice: A Practical Idempotency Guide](https://daily.dev/posts/how-to-stop-charging-customers-twice-a-practical-idempotency-guide-m6qetcboi) · The T-Shaped Dev · 0 upvotes · 1 comments - [Idempotency Is Easy Until the Second Request Is Different](https://daily.dev/posts/idempotency-is-easy-until-the-second-request-is-different-skbwedvu3) · Hacker News · 0 upvotes · 0 comments - [From HTTP Retries to Kafka Redelivery: Building End-to-End Idempotency with FastAPI](https://daily.dev/posts/from-http-retries-to-kafka-redelivery-building-end-to-end-idempotency-with-fastapi-m2qkobimp) · Medium · 0 upvotes · 0 comments - [How to Check Idempotency and Duplicates of Requests in Web Applications](https://daily.dev/posts/how-to-check-idempotency-and-duplicates-of-requests-in-web-applications-ozp46xvld) · Software Testing Magazine · 0 upvotes · 1 comments - [The Idempotent Consumer Pattern in .NET \(And Why You Need It\)](https://daily.dev/posts/the-idempotent-consumer-pattern-in-net-and-why-you-need-it--7cs6q6lwd) · Milan Jovanović · 6 upvotes · 1 comments --- Tags: [#distributed-systems](https://daily.dev/tags/distributed-systems), [#nestjs](https://daily.dev/tags/nestjs) [View this post on daily.dev](https://daily.dev/posts/day-18-30-make-it-idempotent-ifvtwniu1) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"DiscussionForumPosting","mainEntityOfPage":"https://daily.dev/posts/day-18-30-make-it-idempotent-ifvtwniu1","headline":"Day 18/30 — Make It Idempotent","text":"Systems that handle retries, webhooks, and queue redelivery must treat duplicate operations as normal rather than exceptional. Key protections discussed include idempotency keys, unique database constraints, atomic state transitions, stored provider references, and idempotent job processors. 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