Spot VMs in Azure:
Microsoft announces Spot VMs in Azure, using this feature customers can
take benefit of Azure’s unused capacity at lowest cost. Spot VMs
replaces the Low-priority VMs. Azure Spot VMs can be used for testing
purposes, batch processing jobs, large compute workloads, and more.
Don’t get confused about this feature, it’s not a big deal, we will
discuss this feature in this blog
To clear about this feature, we are going to talk over some of the
topics given below.
1.What is Spot VMs in Azure?
Microsoft announced a Spot VMs mainly for utilizing their unused
capacity with the lowest amount than pay as you go. The amount of
available capacity can vary depends on region, size, time and more. But
one thing we need to remember, Azure will evict our VMs at any time.
2. What is the Difference between regular VMs and Spot VMs?
Both are not much distinct, but the difference is Spot VMs have no SLA
(Service Level Agreement, its commitment between service providers and
users), and our VMs will get evicted at any time.
3. How to create this Azure Spot VMs?
When creating VM in the Azure portal you can view the Azure Spot
instance option, if toggle this option to yes, you can see two types of
Eviction.
- Capacity only
- Price or capacity
3.1: what is Capacity only type?
In this Capacity only type your max price is set to pay as you go rate,
and Microsoft will evict our VM when they need the capacity for pay as
you go workloads.
3.2: What is Price or capacity type?
In this Price or capacity type, you have a good option to decide the Max
price that you want to pay per hour. If you decide you want to spend
only a fixed amount and don’t want to spend more for testing purpose, in
this case you can select Price or capacity type.
Azure recommends to select the max price, and also having chance for
getting increase in cost of the instance, in such a situation our VMs
get evicted. And Azure will also evict when Azure needs a capacity for
pay as you go workloads.
4. When our VMs get evicted?
Azure will evict our VMs when our capacity or price is met. When Azure
evict our VM it will send a notification through Azure Scheduled Events
that says “your VM are being evicted and you have 30 seconds to save
your positions and complete shutdown tasks”. Then after 30 seconds, VM
moved to deallocate state, which means VM gets evicted and then we need
to redeploy the evicted VM.
So, it’s time to see when our VM gets evicted, and how we can save our
VM without eviction, let’s talk over the scenario.
4.1: VMs eviction:
Our VMs gets evicted for two reason
- If Azure needs the capacity back, then Azure evict our VMs.
- If the cost of the Spot VM gets increased when compared to the price
you set during deployment.
For example, look at the below image. During deployment, I select the
max price which is Canada central ($0.02220), but currently, the price
of the VM gets increased than the max price we set early, in such a
state our VM gets evicted.
4.2: How to safeguard our VM eviction based on pricing:
If you set the maximum price to -1, then our VM will not get evicted for
pricing reason, because -1 is considered as a current price up to price
for standard VM.
4.3: When our VM get deployed/Vm is not deployed:
| When our VM get deployed | When our VM is not deployed |
|---|---|
| Selecting the Max price greater than the current price. | Setting Max price, which is lesser than the current price, it shows error, that max price needs to be greater than the current price.  |
| Restarting the evicted VM: Selecting the Max price greater than the current price. | Restarting the evicted VM: Setting the Max price, that is lesser than the current price, it shows an error, that the max price needs to be greater than the current price |
And two more scenario we meet:
- After the eviction, if the price for the VM getting back to the
current price, which is lesser than our max price: Now the VM will
not restart automatically, we need to restart by hand. And the
charge is based on the current price. - If you want to change the Max price, then you need to deallocate the
VM and fix the new price and need to update VM by yourself.
5.Restrictions:
- Spot VM will not be supported in B-series, Promo version of any
size. - Spot VM will not be supported In Microsoft Azure China 21Vianet.
- Spot VM does not use ephemeral OS disks.
