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AWS Elastic Compute Cloud (EC2) instances use either paravirtualization or hardware virtualization. While some EC2 instances can run under either type of virtualization, others are only supported by one type. And as Amazon Web Services (AWS) rolls out new instances in its current generation, it is clear that types in the previous generation are all but depreciated.
The technical differences between Amazon's two modes of virtualization were covered previously, but it's also important to understand the relationship between instance types, AMIs and snapshots. When an EC2 instance is created, an Amazon Machine Image (AMI) is created that describes the basic characteristics of the running instance. That AMI is stored as an Elastic Block Store snapshot. It is possible -- though difficult -- to convert an AMI snapshot from one virtualization type to the other.
There are nine instance categories in the current generation: T2, M4, C4, G2, R3, I2, D2, C3 and M3. Only two of those instance categories use paravirtualization (PV): C3 and M3. All of the rest run only on hardware virtualization (HVM) instances.
Amazon is sending a clear message about which direction it is going. In its documentation pages, Amazon states: "HVM AMIs are required to take advantage of enhanced networking and GPU processing. In order to pass through instructions to specialized network and GPU devices, the OS needs to be able to have access to the native hardware platform; HVM virtualization provides this access."
One could reasonably assume that the HVM instance will continue to trend upward in the future.
|Category||Number of sizes||Description|
|T2||3||A baseline level of CPU performance with the ability to burst above the baseline|
|M4||5||Latest generation of general purpose instances|
|C4||5||Latest generation of compute-optimized instances|
|G2||2||Graphics and general purpose GPU compute applications|
|R3||5||Optimized for memory-intensive applications and have the lowest cost per GiB of RAM among Amazon EC2 instance types|
|I2||4||Very fast SSD-backed instance storage optimized for very high random I/O performance and provide high IOPS at a low cost|
|D2||4||Up to 48 TB of HDD-based local storage, deliver high disk throughput and offer the lowest price-per-disk throughput performance on Amazon EC2|
Table 1 includes some HVM types that represent incremental improvements over previous generations, as well as new instance types, such as T2.
T2 instance types are smaller instances that burst to use more system resources when necessary. For this reason, they are known as burstable instances. T2 instances start with an initial credit that can be spent on CPU bursts and acquire more credits as they run in a low CPU utilization mode. If an instance is generally idle but occasionally requires high CPU, the burstable instance fits the bill nicely. For example, a T2.large instance costs approximately 22% less than a comparable M3.large. This capability is only available when using instances based on HVM AMIs.
For enterprises that require large storage, fast disks and low-cost RAM, it's easy to make a case for these HVM instance types. And the trend from Amazon seems clear.
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