The fourth quarter accounts for 40-60% of annual revenue for most e-commerce stores. Black Friday, Cyber Monday and Christmas shopping create traffic that far exceeds the average. Stores that didn’t prepare technically don’t lose orders to competitors – they simply can’t handle the load. Below is the checklist I go through with clients before every season.
Server performance and cache
First thing to verify: is full-page cache (Varnish or Magento FPC) working correctly? Without cache, every request hits PHP and the database – at 10x normal traffic that’s the shortest route to downtime.
- Check cache hit rate – should be above 90% for product and category pages
- Identify URLs that bypass cache (UTM parameters in cookies, session in URL)
- Verify that category pages with price filters cache correctly
- Prepare a cache warm-up scenario for after clearing it
Load testing
Before the season, not during it. Load tests should simulate not just browsing but also add-to-cart and checkout – because checkout is what typically fails first.
- k6 or Locust – simulate 5x, 10x, 20x normal traffic
- Test checkout throughput separately (orders/minute)
- Monitor database response time under high load – missing indexes often surface here
- Check behaviour on payment timeout – does the order remain in a consistent state
External integrations
ERP, payment gateways, couriers, marketing platforms – each integration is a potential point of failure. At 10x traffic, timeouts and rate limits that were never an issue suddenly become critical.
- Contact payment processors and inform them of the expected volume increase
- Check API limits of every integration
- Implement a circuit breaker for non-critical integrations (recommendation engines, for example)
- Test what happens when ERP is unavailable – do orders queue or fail
Monitoring and alerts
Without monitoring Q4 is guesswork. You need to know something is breaking before a customer does.
- Alerts on response time above 2s for key pages
- Alert on 5xx error rate above 0.1%
- Monitor the order queue in ERP – is it growing out of control
- Alerts on out-of-stock products (if you have limited inventory)
- Technical on-call during Black Friday – someone reachable by phone all day
Content and promotions
- Pricing rules: test all coupons and promotions before launch
- Check pricing rule priorities – Magento applies them in order, wrong priority = wrong discount
- Prepare promotional content in advance, not on launch day
- Take a backup before rolling out large configuration changes
Backup and contingency plan
An untested backup is not a backup – it’s hope. Test a restore on staging before the season. Also prepare a customer communication plan for the event of downtime: what you put on the site, who notifies customers who placed orders during the outage.
If you’d like to go through this checklist for your specific store, an initial technical audit is free. Write to biuro@tews.pl or visit tews.pl.
