October is the deadline, not November
Any capacity change - a bigger plan, a new server, a CDN - needs weeks of real traffic on it before the peak. Migrating during the busiest week of the year turns a good problem into an outage.
Set a hard internal freeze date in mid-November: no theme changes, no plugin updates, no new tracking scripts after it.
The technical checklist
Run through this in order during October.
- Load-test at three times your expected peak concurrency, not average traffic.
- Exclude cart, checkout and account pages from full-page caching, and verify with a real purchase.
- Pre-warm the CDN with your campaign landing pages and product images.
- Check database connection limits - they fail before CPU does on most stores.
- Confirm backups run and, more importantly, restore. Test one.
On the day
Have one person watching error rates and checkout completions rather than page speed. A store that is slow but converting is fine; a fast store with a failing payment step is not.
Keep a written rollback for every change shipped in the previous month, and make sure someone other than the developer can execute it.
Takeaway: Capacity you buy in a panic always costs more than capacity you buy in advance.