In this article, we’ll look at the options for the availability of virtual machines in Microsoft Azure. So how can we ensure that our virtual machines are always running in Microsoft Azure, and how can we ensure that they comply with a 99.95% SLA from Microsoft Azure?
We use availability sets with two or more computers with the same role.
The virtual machines in the availability group are automatically distributed between the fault domains and the update domains. They are equally distributed across the three fault domains, for example, FD A, FD B and FD C.
Azure Availability Kit
An availability group is a resource in Azure Resource Manager that provides 99.95% uptime based on an Azure SLA. You need to have two or more virtual machines included.
In addition, we recommend that you organize your servers in an availability set by feature rather than mixing multiple server types in a single availability set. This means that you can have an availability group with only SQL servers and one with only IIS servers.
Here’s an example of two availability sets, each with its own set of servers. As you can see, the servers in the same availability group perform the same function.
Below is an example of two SQL servers in AAG (Azure Application Gateway) in an availability group. Note that the availability set only provides redundancy at the host level; you need to provide clustering on your VM side.
Now let’s go back to the fault domains and update the domains. They are two different things, although they basically work the same way. As we discussed earlier, servers are spread across three fault domains that protect them from infrastructure failures.
For example, hypervisor failures or power outages, etc. The server in FD A will go down, but the servers in FD B and C will continue to run, so you won’t lose service.
Now virtual machines are also distributed among twenty update domains. The update domain is the same as the fault domain. It simply means that machines are protected from basic updates to the hypervisor infrastructure. Hence the name “Update Domains”.
Another thing Microsoft recommends to use is managed disks as storage for servers, as disks will also be shared between fault domains and update domains.
I hope you enjoyed this walkthrough and will post more guides on how to step-by-step setting up an availability set in Azure. Enjoy!