What is high availability?
High availability refers to fulfilling a user request with reliability and without loss of service.
High availability uses failover mechanisms to mitigate the risk that any request is returned with an error or failure. Usually load balancing is used to manage traffic efficiently to individual servers in a high-availability configuration.
High availability is measured in terms of percentage of seconds of uptime, that is, how often the service is available and what that translates to in downtime per year.
In Varnish, it is a multi-master replication service that allows you to replicate content between Varnish servers. As Varnish gets a new object from the backend it will replicate the object over to its peer cache. Since both servers now have the object they can both serve it to clients, removing the need to seek the object from the backend.
Discover and learn more about Varnish high availability.