Why zero downtime is now mandatory

Downtime during login or checkout directly harms trust and revenue. In 2026, strong PHP teams treat deployment as a repeatable operating system, not a one-time script.

Production-safe release model

Use immutable release directories and an atomic symlink switch:

  • build and validate each release before traffic
  • keep current pointing to the active release
  • switch instantly only after all checks pass

This gives faster rollout, safer rollback, and clear release history.

Database changes without breaking users

Use an expand-contract approach:

  1. add compatible schema changes first
  2. deploy code that supports old and new structures
  3. migrate data in controlled batches
  4. remove deprecated fields only after full validation

Never combine destructive schema changes with the same critical release.

Post-deploy verification

After traffic switch, verify immediately:

  • health endpoint and error rate
  • p95 latency for critical routes
  • queue and worker stability
  • core user journey (login, search, checkout)

Rollback discipline

A rollback plan is useful only if tested. Keep rollback to one command path, run drills quarterly, and document responsibilities per role.

Conclusion

Zero downtime is not a single tool. It is a process: compatible migrations, strict preflight checks, staged verification, and proven rollback.