A burstable instance is a virtual machine (VM) instance that provides a baseline level of CPU performance with the ability to burst to a higher level to support occasional spikes in usage.
How Burstable Instances Work
Burstable instances are able to sustain workloads running at a fraction of CPUs most of the time, and can burst up to the full CPUs for a limited amount of time.
When you create a burstable instance, you specify the total OCPU count (or CPU cores) and the baseline CPU utilization. The baseline utilization is a fraction of each CPU core, either 12.5% or 50%. The baseline provides the minimum CPUs that can be used constantly.
When needed, the instance can use more than the baseline CPU, all the way up the total OCPUs that you provision. This usage above the baseline is called bursting, because it happens automatically and for short periods of time.
The ability to burst depends on the instance’s CPU usage pattern and the underlying server resource usage. If the instance’s average CPU utilization over the past 24 hours is below the baseline, the system will allow it to burst above the baseline.
After the burst is finished by the system, the instance is limited to the baseline CPU.
Limitations and Considerations
- For critical or production workloads that require full OCPU utilization, you should use a regular instance instead. Because the physical VM host is oversubscribed, there is no guarantee that an instance will be able to burst.
- Network bandwidth is oversubscribed, so there is no guarantee that the instance can use the maximum bandwidth.
- Memory does not burst.
- Custom images are supported if the baseline OCPU meets the minimum requirements for the image.
- Each burstable instance can have one ephemeral public IP address. If you need additional public IPs, assign reserved public IPs to the instance.
- You can attach four block volumes for each 12.5% baseline OCPU, up to the maximum limit.
- Burstable instances must use paravirtualized networking.
- Burstable instances are not supported on dedicated virtual machine hosts, capacity reservations, or preemptible capacity.
- Burstable instances and regular instances share the same service limits and compartment quotas based on the instance’s shape.
OCPU, Memory, Network Bandwidth, and VNICs
Because burstable instances use flexible shapes, you can customize the number of OCPUs and the amount of memory that are allocated to a burstable instance.
- OCPUs: You can select the same range of OCPUs for a burstable instance as you can select for a regular instance that uses the same shape.
- Memory: The amount of memory is based on the total number of OCPUs. For each OCPU, you can select the same ratio of memory for a burstable instance as you can select for a regular instance that uses the same shape, regardless of which baseline OCPU you configure.
- Network bandwidth: The maximum network bandwidth is defined in relation to the baseline OCPU. Network bandwidth does burst.
- VNICs: The minimum number of VNICs, maximum number of VNICs, and ratio of VNICs to OCPUs for a burstable instance are the same as those for a regular instance that uses the same shape.
Supported Shapes
You can use the following shapes to create burstable instances:
- VM.Standard3.Flex
- VM.Standard.E3.Flex
- VM.Standard.E4.Flex
I will prepare a post on how to implement this feature.
Hope this helps you!!!
Disclaimer: “The postings on this site are my own and don’t necessarily represent may actual employer positions, strategies or opinions. The information here was edited to be useful for general purpose, specific data and identifications was removed to allow reach generic audience and to be useful