GCP Preemptive VMs and Custom VMs
GCP-Preemptive VMs and Custom VMs
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Preemptive VMs and Custom VMs
Introduction to short-lived VMs.
We'll cover the following
Preemptive VM
Custom VMs
Compute engine terms
Instance
Machine types
Images
Image family
Snapshots
Metadata
What is a preemptible instance?
Preemptible VM instances are available at much lower price—a 60-91% discount—compared to the price of standard VMs. However, Compute Engine might stop (preempt) these instances if it needs to reclaim the compute capacity for allocation to other VMs. Preemptible instances use excess Compute Engine capacity, so their availability varies with usage.
If your apps are fault-tolerant and can withstand possible instance preemptions, then preemptible instances can reduce your Compute Engine costs significantly. For example, batch processing jobs can run on preemptible instances. If some of those instances stop during processing, the job slows but does not completely stop. Preemptible instances complete your batch processing tasks without placing additional workload on your existing instances and without requiring you to pay full price for additional normal instances.
Preemptible instance limitations
Preemptible instances function like normal instances but have the following limitations:
Compute Engine might stop preemptible instances at any time due to system events. The probability that Compute Engine stops a preemptible instance for a system event is generally low, but might vary from day to day and from zone to zone depending on current conditions.
Compute Engine always stops preemptible instances after they run for 24 hours. Certain actions reset this 24-hour counter.
Preemptible instances are finite Compute Engine resources, so they might not always be available.
Preemptible instances can't live migrate to a regular VM instance, or be set to automatically restart when there is a maintenance event.
Due to the preceding limitations, preemptible instances are not covered by any Service Level Agreement and are excluded from the Compute Engine SLA.
The Google Cloud Free Tier credits for Compute Engine do not apply to preemptible instances.
Preemption of preemptible VMs
This section describes how preemptible VMs are preempted by Compute Engine and which VMs are selected for preemption.
Preemption process
Compute Engine performs the following steps to preempt an instance:
Compute Engine sends a preemption notice to the instance in the form of an ACPI G2 Soft Off signal. You can use a shutdown script to handle the preemption notice and complete cleanup actions before the instance stops.
If the instance does not stop after 30 seconds, Compute Engine sends an ACPI G3 Mechanical Off signal to the operating system.
Compute Engine transitions the instance to a TERMINATED state.
You can simulate an instance preemption by stopping the instance.
Preempted instances still appear in your project, but you are not charged for the instance hours while it remains in a TERMINATED state. You can access and recover data from any persistent disks that are attached to the instance, but those disks still incur storage charges until you delete them. As with normal instances, persistent disks that are marked for auto-delete are deleted when you delete the preemptible instance. You can restart a preempted instance as many times as you would like, as long as there is capacity. Restarting a preemptible instance resets the preemptible process.
If Compute Engine stops a preemptible instance less than one minute after it is created, you are not billed for the use of that VM instance. This ensures that you don't pay for preemptible instances unless they have had time to complete a significant amount of work. However, the charges for premium operating systems are still calculated as normal.
What is a preemptible instance?
Preemptible VM instances are available at much lower price—a 60-91% discount—compared to the price of standard VMs. However, Compute Engine might stop (preempt) these instances if it needs to reclaim the compute capacity for allocation to other VMs. Preemptible instances use excess Compute Engine capacity, so their availability varies with usage.
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