So why should we implement passive node's the role of the passive notice to monitor the availability
of the active node and the service provided by the node.
If they are unavailable the passive node activates this requires at least two computers the active and
passive nodes to be connected.
They need to share a local area network which is dedicated to checking the availability of the two nodes
best practices show that an active node availability test is of key importance for the entire fell over
cluster
knowingness.
You shouldn't use a public web interface for the purpose.
If the active node was a file server that receives and sends huge amounts of data it might not be able
to answer an availability query in time as a consequence the service would fail over to the passive
node which is of course something we wouldn't want
other than the active and passive nodes.
There are also shared resources in a service fail over cluster.
This is a location to which an active node saves changes in its configuration.
This implies that it's not enough to have two computers and a system that supports clustering a service
that is protected with these measures must also support clustering.
It has to log all changes in configuration and quorum files.
The changes are asynchronous which means they occur only in one active node
This explains why if there is a fail and a fail over following a change in settings the passive node
might not acknowledge and implement the changes.
This could lead to a system inconsistency
the quorum which only the active node can access is capable of synchronizing both services.
Imagine that because of a virus or detected intrusion or a simple failure we need to shut down the computer
or stop running a service.
What can be done to restore the services.
There are a few options to choose from.
The first solution which is also the safest and most recommended option is re-installation the drawback
of re-installation is that it is unfortunately also the most time consuming solution.
To reinstall a system we need to use disks that we've checked and are sure they have not been modified.
We need to raise data from all hard disks of a compromised computer.
We have to do this because we're not sure whether or not the files have been modified.
It's far easier to delete all data and reinstall the system than find one modified file.
The second option is recovering a computer system and installed services from backups to be able to
recover a system we need to have made backups on a regular basis.
The strategy for creating backup copies will be covered later.
The files that are saved in those backups have to be trustworthy.
We need to be fully sure that the copy has been made before an attack from which we're recovering took
place.
Otherwise recovering files from a backup doesn't make sense.
This suggests that it's necessary to keep more than one backup of your infrastructure.