Costco's website experiences downtime for a few common reasons. The most frequent cause is traffic overload during major sales events like Black Friday, Boxing Day, or flash sales on high-demand items. When millions of users hit the site simultaneously, even enterprise-level infrastructure can struggle. Costco also schedules periodic maintenance windows, typically during off-peak hours, to update systems or apply security patches. Technical issues like CDN failures, DNS propagation problems, or database errors can also take the site offline temporarily. These usually resolve within 30 minutes to a few hours. If the outage affects only certain regions, it's often a CDN edge server issue rather than a core infrastructure problem. Before assuming Costco's site is actually down, rule out local issues. Check your internet connection, try a different browser, clear your cache and cookies, or test from your phone on cellular data. Sites like downdetector.com or isitdownrightnow.com can confirm whether others are experiencing the same problem. For e-commerce sites handling Costco's transaction volume, we see similar patterns with our portfolio clients during seasonal peaks. The difference is scale. A site doing $200 million annually might see 50,000 concurrent users during a sale. Costco processes billions and can see 10x that traffic. If you're running your own e-commerce operation, the lesson is clear: load test before major promotions, use a robust CDN with multiple edge locations, and have fallback systems ready. At Ottawa SEO, we configure caching layers and CDN rules specifically to handle traffic spikes without taking sites offline. A properly configured WordPress or Shopify site on solid infrastructure should handle 10-20x normal traffic without breaking, but that requires planning, not just hoping your host can take it.