Explain advanced zero-downtime deployment strategies for PHP systems.

Zero-downtime deployment techniques allow PHP applications to release updates without interrupting live traffic.

High availability systems require continuous uptime during deployments.

Deployment strategies:

Two identical environments switch traffic.

Gradual rollout to subset of users.

Gradual pod replacement.

Runtime toggling of features.

Test production traffic silently.

Challenges:

Backward compatibility required.

Users must not be disrupted.

Old and new versions coexist.

4.…