--- title: "Prevent HTTP DDoS With Cloudflare - Black Friday DDoS Defense Notes" description: "A real-world account of an e-commerce site responding to DDoS attacks during Black Friday, showing how to configure allowlists, blocklists, country challenges, and rate limiting in Cloudflare WAF for successful defense." canonical_url: "https://blog.markkulab.net/en/post/prevent-ddos-part2" author: "Mark Ku" author_url: "https://blog.markkulab.net/en/author/mark-ku" site: "Mark Ku's Tech Notes" date_published: "2022-11-28 01:01:01 +0800" category: "Security" tags: ["ddos", "cloudflare", "waf", "security", "black friday", "ecommerce", "firewall"] 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" --- # Prevent HTTP DDoS With Cloudflare - Black Friday DDoS Defense Notes ## Background I currently work at an e-commerce company whose products mainly serve the US, Germany, and Canada. A few days before Black Friday, we noticed that the site was constantly being hit by DDoS attacks. One day the site went down completely, which is when we started a deeper investigation. [I previously wrote an article](https://blog.markkulab.net/2022/01/16/prevent-ddos/) on DDoS defense concepts. This post applies those defense rules in Cloudflare WAF. ### Reviewing Cloudflare's security report, on the 12th we received roughly 20 million malicious requests targeting our site. ![Cloudflare Firewall Events dashboard showing country totals and event timeline](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/nANZAqj.png) ![Cloudflare WAF security report showing blocked, challenged, and allowed requests](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/pmtPE3Z.png) ### Thinking about it from a sysadmin's perspective, many questions came to mind. Why would a single IP make such a huge volume of requests? ![Top IP addresses by event volume with bar graphs](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/ZZcMKIn.png) ### And why are there so many countries we don't even operate in sending heavy traffic to our site? ![Table of top threat countries by request volume](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/fd3Hjn1.png) ### Although we use the Enterprise tier of Cloudflare, the default settings - while blocking most DDoS - still let some attacks slip through given the sheer volume. I spent a lot of time learning Cloudflare, reviewed every setting, discussed with my boss, and then put together a DDoS prevention plan using Web Application Firewall rules to protect our business during Black Friday, with our US boss's approval. ![Cloudflare DDoS prevention rules table with festival and last resort actions](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/Gd5SfbS.png) ### To avoid false positives that hurt the business, we only blocked single IPs making excessive requests. Below is the block screen. ![Cloudflare access denied error 1020 block screen on mobile](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/DhNvfeN.png) ### To avoid false positives, before adding an IP to the blocklist we look it up and report it on [abuseipdb](https://www.abuseipdb.com/check/34.121.210.98). ![AbuseIPDB report for IP 34.121.21](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/m3kgWmU.png) ### For other rules, to avoid false positives that affect orders, we only enable human verification. Users must pass it before entering the site. ![Mobile screen showing Cloudflare hCaptcha security check for ibuypower.com](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/icKvFKYl.png) ![Human verification CAPTCHA on mobile, select hot air balloons](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/ZrxS5ZUl.png) ## Now let's start creating WAF rules - Create Firewall rules ### Go to Cloudflare admin > Security > WAF > Create firewall rule ![Cloudflare WAF rules page, Create firewall rule button highlighted](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/W9JrIh1.png) #### Rule 1. Allowlist - White List ![Cloudflare WAF edit firewall rule screen for whitelisting known bots](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/jCN1Q5Q.png) #### Rule 2. Blocklist - IP Block (attacker) ![Cloudflare WAF rule blocking listed attacker IP addresses](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/CggFyEH.png) #### Rule 3. Country challenge ![Cloudflare WAF rule challenging traffic from Brazil, China, India, Indonesia, Ru](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/CnZ7q6V.png) #### Rule 4. IP Challenge (suspicious) ![Cloudflare WAF editing a suspicious IP challenge firewall rule](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/4dMWWvS.png) #### Rule 99. Bot challenge - Automated (last resort) ![Cloudflare WAF editing an automated bot challenge firewall rule](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/b8SdAzv.png) #### Rule 99. Likely automated challenge (last resort) ![Cloudflare WAF editing a bot challenge firewall rule](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/1PDyWAK.png) #### Rule 99. Request rate limit (last resort) ![Cloudflare WAF editing a request rate limiting rule with managed challenge](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/7yXmDJ1.png) #### Rule 100. Only allow operating countries - Non-operating country ![Cloudflare WAF firewall rule blocking non-operating countries](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/ktMCQCe.png) #### You can also tune DDoS sensitivity (Security > Settings > DDoS > Configure > Security Level > Medium) ![Cloudflare dashboard displaying DDoS L7 ruleset sensitivity configuration](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/20.png) #### If nothing else holds, you can turn on "I'm Under Attack" mode. All users wait five seconds before entering the site. Remember to switch it back when done. Security > Settings > DDoS > Configure > Security Level > Enable I'm Under Attack mode ![Cloudflare security settings with I'm Under Attack mode enabled](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/21.png) ## Effectiveness Across Thanksgiving and Black Friday (three days), we faced 7 DDoS attacks totaling more than 13 million malicious requests, with the highest single burst hitting 3 million requests at once. After the fifth attack the site stalled for about 30 seconds. The reports showed the attack pattern shift from concentrated IPs and countries to small, dispersed traffic. We finally decided to leverage Cloudflare's machine-learning-based rules. Without hurting the business, only single IPs sending massive request volumes were outright blocked, while everything else was sent to human verification. We made it through this year's Black Friday smoothly. It was a pretty intense Black Friday - many external services also experienced anomalies. ### A total of 13.63 million requests received ![Cloudflare Firewall Events dashboard showing Black Friday DDoS defense statistic](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/RZijw3y.png) ### WAF helped block over 5 million requests ![Cloudflare WAF rules table showing activity and challenge metrics](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/yLnNpgS.png) ### Bot analytics report ![Cloudflare Bot Analytics bar chart of requests by bot score on Black Friday](https://blog.markkulab.net/content/markku/posts/prevent-ddos-part2/images/q9OEuh6.png) --- ## About this article and its author Originally published on [Mark Ku's Tech Notes](https://blog.markkulab.net/en/post/prevent-ddos-part2) 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. Everything runs in your browser; nothing is uploaded. - [VS Code Refactory](https://blog.markkulab.net/en/tools/refactory): Refactory is a VS Code refactoring extension: 34 actions plus a 37-rule code-smell inspection layer with a Code Health dashboard, across 18 languages, backed by 534 tests. It learns your repo's conventions: where interfaces live, where DI is registered, whether 'use client' belongs. It ranks files by git churn × complexity so you know what to fix first, and hands any smell to the Claude Code already on your machine. Free to use, and your source never leaves your computer. - [DB-Kit Database Manager](https://blog.markkulab.net/en/tools/db-kit): DB-Kit is a lightweight, cross-platform database manager built with Tauri + Rust + React. Manage MySQL, MariaDB, PostgreSQL, SQL Server, Oracle, SQLite, MongoDB, Redis, Kafka, Elasticsearch and RabbitMQ from one consistent interface: passwords encrypted in the OS keychain, SSH tunnels, full CRUD, a visual query builder, stacked multi-statement result sets, cross-connection data transfer and compare/sync, Excel / CSV import & export, visualized execution plans, ER diagrams, scheduled backups, SQL stress testing with p50–p99 latency percentiles, a 15-rule SQL review engine, Kafka message browsing with monitoring & alerts, a bilingual UI (Traditional Chinese / English), a built-in AI assistant (natural-language SQL, AI review and tuning advice) and the dbk CLI. 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No sign-up, nothing uploaded to a server, and mermaid.live share links work as-is. - [React Intl Phone Number](https://blog.markkulab.net/en/tools/react-intl-phone-number): react-intl-phone-number is an open-source React component: framework-agnostic and antd-free, with E.164 in/out, a searchable flag / country-code dropdown, configurable validation levels (strict / mobile-strict / loose), themeable CSS, and i18n — phone logic powered by google-libphonenumber. Lightweight and fully typed. Free and open source (MIT). - [Uptime Kuma Cluster](https://blog.markkulab.net/en/tools/uptime-kuma-cluster): Turn single-node Uptime Kuma into a highly available cluster: OpenResty + Lua smart load balancing, shared MariaDB state, health checks and automatic failover, plus cluster-management REST APIs. One Docker Compose command to start. 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