Availability Sets is designed to provide high availability of your application in terms of ensuring the protection of your application from power failure, network failure, downtime due to software patch updates.
You need to have multiple VMs like Web vm1/ Web vm2..., App vm1/ App vm2...., DB vm1/DBvm2.....
If you want to leverage 99.95% SLA from Microsoft you must place your VMs inside availability set. Your VMs must use Microsoft managed storage(premium storage).
Fault Domain: VMs in a fault domain share the same rack, network, power supply. It means when a fault domain fails all VMs inside that fault domain go down.
So the Availability Set arranges Web vm1 in FD0, Web vm2 in FD1, and so on.
Availability Set by default has 3 Fault Domains
Update Domain: It is a logical unit. All VMs that reside in an Update Domain get software updates, patch updates, reboot altogether.
So the Availability Set arranges Web vm1 in UD0, Web vm2 in UD1, and so on.
Availability Set by default has 5 Update Domains
The sequence could be any but at a time only one Update Domain gets updated and rebooted, with given 30 min downtime.
MS Reference https://docs.microsoft.com/en-us/azure/virtual-machines/windows/tutorial-availability-sets
You need to have multiple VMs like Web vm1/ Web vm2..., App vm1/ App vm2...., DB vm1/DBvm2.....
If you want to leverage 99.95% SLA from Microsoft you must place your VMs inside availability set. Your VMs must use Microsoft managed storage(premium storage).
Fault Domain: VMs in a fault domain share the same rack, network, power supply. It means when a fault domain fails all VMs inside that fault domain go down.
So the Availability Set arranges Web vm1 in FD0, Web vm2 in FD1, and so on.
Availability Set by default has 3 Fault Domains
Update Domain: It is a logical unit. All VMs that reside in an Update Domain get software updates, patch updates, reboot altogether.
So the Availability Set arranges Web vm1 in UD0, Web vm2 in UD1, and so on.
Availability Set by default has 5 Update Domains
The sequence could be any but at a time only one Update Domain gets updated and rebooted, with given 30 min downtime.
Assignment of FD and UD to VMs takes place as given below
Virtual Machines
|
Fault Domain (3 Fault doamins)
|
Update Domain (5 Update domains)
|
VM 1
|
0
|
0
|
VM 2
|
1
|
1
|
VM 3
|
2
|
2
|
VM 4
|
0
|
3
|
VM 5
|
1
|
4
|
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