Moving one WordPress site is easy. Moving twenty in a weekend is a pipeline, and the failures that cost you are the quiet ones: writes landing on the old server, cron firing on two boxes, certificates blocked by ACME rate limits. Here is the fleet migration process I use, from manifest to per-site rollback.
Migrations rarely fail loudly. The site stays up while mail, cron, certificate renewal and the write path break silently behind it. A post-migration checklist for the first 48 hours, ordered by how long each failure can hide rather than by subsystem.
Benchmarks pick the wrong winner. Here is how Nginx, Apache and Caddy actually differ in production: how each one fails under load, who owns certificate renewal, and where configuration lives when a developer needs to change it. Includes a decision procedure and the mistakes I see most.
Your browser shows a padlock and your partner's API client throws "unable to get local issuer certificate". Both are correct. A practical guide to the four things a TLS client actually checks, and to renewal automation that reaches the running server instead of just the disk.
Almost every TLS certificate error traces back to one of three causes: a broken chain, a hostname the certificate does not cover, or an expiry nobody was watching. Here is how to tell them apart in under a minute, and how to stop the third one from ever happening again.