WHAT IS HIGH AVAILABILITY
The capacity for downtime due to hardware, software, network failure
makes high availability hosting solutions an attractive feature from Empire
High availability solutions can be categorized into local high availability
solutions that provide high availability in a single data center deployment,
and disaster recovery solutions, which are usually geographically, distributed
deployments that protect your applications from disasters such as floods
or regional network outages.
Amongst possible types of failures, process, node, and media failures
as well as human errors can be protected by local high availability solutions.
Local physical disasters can be protected by geographically, distributed
disaster recovery solutions.
To solve the high availability problem, a number of technologies and
best practices are needed. The most important mechanism is redundancy.
High availability comes from redundant systems and components. Local high
availability solutions can be categorized, by their level of redundancy.
Active-passive solutions deploy an active instance that handles requests
and a passive instance that is on standby. In addition, a heartbeat mechanism
is set up between these two instances. This mechanism is provided and
managed through operating system vendor-specific clusterware. Generally,
vendor-specific cluster agents are also available to automatically monitor
and failover between cluster nodes, so that when the active instance fails,
an agent shuts down the active instance completely, brings up the passive
instance, and application services can successfully resume processing.
As a result, the active-passive roles are now switched. The same procedure
can be done manually for planned or unplanned down time. Active-passive
solutions are also generally referred to as cold failover clusters.
In some instances, HA hosting may not sufficiently accomplish all your
disaster prevention and redundancy goals. For example, some businesses
need fault tolerant or geographical site protection from disasters. In
these cases customer can leverage Empire Hosting's DNS active failover
across geographically dispersed sites to ensure consistent business continuity
of critical services and applications. Once HA has recovered impacted
servers onto healthy hardware the DNS for critical services can be redirected.