--- title: Best System Design Codex posts — October 2025 | daily.dev description: The most upvoted System Design Codex posts from October 2025, curated by the daily.dev community. canonical: https://daily.dev/sources/systemdesigncodex/best-of/2025/10 twitter:card: summary_large_image twitter:site: @dailydotdev og:url: https://daily.dev/sources/systemdesigncodex/best-of/2025/10 og:type: website og:site_name: daily.dev og:title: Best System Design Codex posts — October 2025 | daily.dev og:description: The most upvoted System Design Codex posts from October 2025, curated by the daily.dev community. og:image: https://media.daily.dev/image/upload/s--VAY5ToZt--/f_auto/v1724209435/public/daily.dev%20-%20open%20graph --- # Best of System Design Codex — October 2025 1. 1 [](https://daily.dev/posts/authorizing-10-million-api-calls-per-second-u9c5eng3l "Authorizing 10 Million API Calls Per Second") Article System Design Codex · 46w Authorizing 10 Million API Calls Per Second LinkedIn handles authorization for tens of millions of API calls per second using Access Control Lists (ACLs) with an in-memory authorization client on each service. ACL data is stored in Espresso database with Couchbase caching, synchronized via Brooklin change data capture. Authorization checks are logged asynchronously through Kafka for monitoring and auditing. The system balances fast authorization checks, timely ACL updates, efficient data management, and comprehensive monitoring at massive scale. 116 1 [See all System Design Codex archives](/sources/systemdesigncodex/best-of) ```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","@graph":[{"@type":"CollectionPage","@id":"https://daily.dev/sources/systemdesigncodex/best-of/2025/10#page","url":"https://daily.dev/sources/systemdesigncodex/best-of/2025/10","name":"Best System Design Codex Posts — October 2025","description":"The most upvoted System Design Codex posts from October 2025, curated by the daily.dev community.","isPartOf":{"@type":"WebSite","url":"https://daily.dev"}},{"@type":"ItemList","@id":"https://daily.dev/sources/systemdesigncodex/best-of/2025/10#items","numberOfItems":1,"itemListElement":[{"@type":"ListItem","position":1,"url":"https://daily.dev/posts/authorizing-10-million-api-calls-per-second-u9c5eng3l","name":"Authorizing 10 Million API Calls Per Second"}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Sources","item":"https://daily.dev/sources"},{"@type":"ListItem","position":3,"name":"System Design Codex","item":"https://daily.dev/sources/systemdesigncodex"},{"@type":"ListItem","position":4,"name":"Best of","item":"https://daily.dev/sources/systemdesigncodex/best-of"},{"@type":"ListItem","position":5,"name":"October 2025"}]}]} ```