In a cold failover, load balancing systems send a heartbeat to the nodes to check if they are still running. This heartbeat can be configured in the application server and can be sent each minute, or once every two minutes or so. When the server is down, it sends a notification to the load balancer and moves the sessions to another server. The session information that is not stored or committed to database is lost.
In case of high available applications, we can enable failover by changing the passivation setting to use shared storage (Changing storage/class/passivation: /rootpath). This setting is usually set using the dynamic system settings. When configured, the requestors accessing a JVM are redirected to another JVM through the load balancer when the server crashes. The user must authenticate again to establish their session in the new node. All information that is not committed is lost in the process.
Thus, a cold failover is a situation when one of the servers is down and its sessions are moved to the other one. Servers are being controlled by application server sending heartbeats, ok. But what's a hot failover in this case? I've failed to find any information concerning this neither in course book nor in High Availability Documentation, nor in PDN.
***Updated by moderator: Lochan to move post from PSC to Pega Academy***
I had the same doubt while I was going through LSA course, I feel its the other way around. In hot standby, basically there will be a server ready on standby to take the baton from the primary server when it goes down. The description given in the 'Failover or Unplanned outages' lesson is for Hot failover as we always demand for a quicker recovery.
Hot failover is a redundant method in which one system runs simultaneously with an identical primary system. Upon failure of the primary system, the hot standby system immediately takes over, replacing the primary system. However, data is still mirrored in real time. Thus, both systems have identical data.
Hot failover is also known as hot spare, especially at the component level, such as a hard drive in a disk array.