--- title: "Redis on Black Friday" description: "An incident analysis of a Redis master-replica sync failure that froze the shopping cart during Black Friday traffic spikes, along with short-, medium-, and long-term remediation plans including resource tuning, Nginx migration, and Redis Cluster planning." canonical_url: "https://blog.markkulab.net/en/post/redis-black-friday" author: "Mark Ku" author_url: "https://blog.markkulab.net/en/author/mark-ku" site: "Mark Ku's Tech Notes" date_published: "2023-11-27 01:01:35 +0800" category: "Infra" tags: ["redis", "black friday", "ecommerce", "performance", "docker", "monitoring"] language: "en" license: "CC BY 4.0" license_url: "https://creativecommons.org/licenses/by/4.0/" attribution: "when reusing or quoting, credit the author and link back to the original" --- # Redis on Black Friday ## Incident On Black Friday (US time) 2023, I got a call early in the morning. The site was running discounts of $400–650 USD, and a massive wave of traffic hit all at once — orders were coming in every second, many times the normal volume. The site loaded pages fine, but failed to retrieve real-time inventory from Redis correctly. This left users stuck on a loading spinner while the cart waited for inventory data from Redis, preventing them from adding items to their cart. ![image](https://blog.markkulab.net/content/markku/posts/redis-black-friday/images/2.png) ### Root Cause Analysis Investigation revealed that three Redis instances were experiencing sync failures. After analyzing hardware performance, we found that these three Redis slave containers were all running inside a nested Hyper-V host. They shared a single NIC, and the Windows host had only 16 GB of RAM allocated — with Docker Desktop capped at 8 GB. Utilization was near 100% across the board. The conclusion was that insufficient memory was the primary cause of the sync anomaly. As an immediate fix, we shut down one Redis container on that host to free up resources so the remaining containers could operate normally. ![image](https://blog.markkulab.net/content/markku/posts/redis-black-friday/images/3.png) ## Remediation Plan ### Short-Term - Shut down one instance to allow the host to function properly. - Increase available memory. ### Medium-Term - Replace the resource-heavy nested Hyper-V setup with Nginx. - Tune Redis cache eviction settings to release memory from unused keys. ### Long-Term - Consider adopting Redis Cluster with sharding. - Replace Windows Server containers with Linux containers. - Introduce Kubernetes for automated deployment, scaling, and container management. ## References * [Redis的主从复制是如何做的？复制过程中也会产生各种问题？](https://juejin.cn/post/7151593533130948621) * [Redis 的缓存淘汰机制（Eviction）](https://www.cnblogs.com/buttercup/p/13888110.html) --- ## About this article and its author Originally published on [Mark Ku's Tech Notes](https://blog.markkulab.net/en/post/redis-black-friday) License: [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/) — when reusing or quoting, credit the author and link back to the original ### About the author **[Mark Ku](https://blog.markkulab.net/en/author/mark-ku)** — Software Solution Provider - 10+ years senior software engineer, now an AI Builder - Focused on large-platform architecture — North-American e-commerce, AI SaaS subscription billing - Combining AI Agents and automation to build evolvable product foundations ### Free tools built by the author All of these are free to use: - [Free PDF Sign Tool](https://blog.markkulab.net/en/tools/pdf-sign): Online PDF sign tool — draw, type, or upload a signature, then drag, resize, and download. 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