Glossary Terms

high availability

High availability is designing a system so it keeps running even when an individual part fails, by removing any single point that could take the whole thing down. For WordPress that usually means several web servers behind a load balancer, a replicated database, shared file storage every server can reach, and a central object cache, so losing one server doesn't lose the site. A plain single-server install is the opposite: if that one server reboots or crashes, the site is down until it comes back. Enterprise hosts like WordPress VIP, WP Engine Enterprise, and Pantheon build high availability in by default, usually with uptime guarantees of 99.95 percent or better.