When a company makes a transition to a public or hybrid cloud , it must inevitably choose a public cloud provider to host its virtual machines. And while there are many infrastructure providers as a service ( IaaS ), each has its strengths and weaknesses. In addition, each public cloud provider has its own rate grid, and the cost of running a VM in the cloud can be very different from one to the other.
This article is the third in a series that analyzes step by step the process of purchasing virtual server services from a public cloud. The first article described the benefits of hosting virtual servers in the cloud, while the second detailed the costs and risks of a public cloud.
In this article, we review the purchase criteria to be considered in a call for tenders to be sure to get the services adapted to your environment from a supplier.
The fourth article will compare the virtual server services of a public market-leading cloud against established purchase criteria and the services of other providers. This comparison will help you determine which ones offer the best features and the best price for your needs.
Determining the costs of a public cloud
New users of a public cloud are often surprised to learn that IaaS has a complicated pricing grid. You will rarely, if ever, get fixed rates for hosting a virtual machine (VM) in the cloud. And even if a cloud provider publishes the formula for calculating its rates, it is usually extremely complex, which makes it difficult to estimate the cost of hosting a VM in a public cloud.
These formulas are complex because they depend on the resources consumed by VMs. Factors taken into account in public cloud pricing structures are CPU consumption, the type of activity performed by the CPU, bandwidth consumption , storage I / O consumption , system selection operation, type of storage and storage consumption per GB.
Before running a VM in the cloud, set up trial accounts with different cloud providers. This will create identical VMs in each cloud and track costs before comparing pricing from one provider to another.
However, for this method to work, VMs should be as representative as possible of those you will be running in your production environment.
Migrating VMs to the Public Cloud
Another important element to consider is support for VM migration. Most organizations have on-premise VMs that they plan to migrate to the public cloud. Leading public cloud providers offer ways to migrate VMs to the cloud, but some are easier than others. Indeed, in some cases you can operate via a graphical interface, while in others you will have to run a program.
Support for hypervisors also varies widely between different public cloud providers. For example, some of them make it easy to import VMware VMs , but do not support Citrix VMs.
Learn about VM migration costs. Most public cloud providers charge you for the resources you use, including the storage space occupied by new VMs. Some, especially the smaller ones, charge extra fees for importing VMs.
Support for custom images
All public cloud providers allow you to create VMs from precompiled generic images. But because they are generic, these images may not fully meet your needs. For example, you may want to create VM images that include your favorite antivirus software, or that follow specific security policies.
These custom VM images make it easy to configure VMs to suit your needs and to replicate these configurations on future VMs. However, if you plan to create custom VMs in the cloud, make sure your provider supports this process. And even though major public cloud providers do, importing these images is easier for some than for others. If you plan to use a smaller vendor, find out about its support for custom VM images before you sign.
Although all public cloud providers allow you to create generic VMs from predefined models, the complexity and number of these models vary enormously.
In general, generic VM models include an operating system and possibly provide the ability to create application servers. Vendors do not always offer the same operating systems or applications, assuming they even offer applications. Most major public clouds allow you to create Windows and Linux VMs, even if the Windows Server and Linux offered vary.
If you plan to use a small vendor, verify that its model catalog provides for the deployment of the IT environments and applications that you need.
Another important feature to consider when evaluating a cloud provider is autoscaling.
The basic idea of autoscaling is that server workloads are rarely linear. Sometimes, companies experience peaks of activity, for example during periods of subscription for insurance companies or parties for online sales companies . Other times, the demand is much smaller.
Autoscaling enables VMs to increase their performance when the workload is heavier, and to reduce them when there is room for cost savings.
Autoscaling varies across cloud platforms. Some vendors only offer this feature for web applications by hosting additional Web servers online. Others increase VM memory space and processing resources for sizing the workload. This can be done manually, or automatically using a set of rules, performance indicators, or a schedule.
Each cloud service provider offers network connectivity for VMs. It goes without saying that your VMs will be able to access other VMs and the Internet.
Despite this, large cloud providers typically offer several network connectivity options.
They vary by vendor, but usually they are high-end connectivity options that allow VMs to receive higher levels of network performance. These options are especially useful for VMs running applications that are sensitive to network latency.
If you plan to run cloud and latency-aware applications, be sure to find out about the network connectivity options for your potential cloud provider.
In the same way that all cloud providers offer basic network connectivity for VMs, they offer basic VM storage options. After all, VMs use virtual hard disks, and you have to put them somewhere. Many cloud service providers also offer options in addition to basic entry-level storage.
Storage services vary greatly from one provider to another, but in general they include at least standard and high-end options. The largest cloud providers tend to offer a lot of customization possibilities as part of their high-end storage. For example, customers may be able to choose between rotational storage and SSD storage , though the latter is almost always more expensive.
High-end storage can also include fault-tolerant options. Some cloud service providers allow you to replicate storage or create virtual storage arrays that boost performance and ensure fault tolerance. Although rare, some providers also give you the option of using high-end storage to create VM snapshots or backup targets.
When evaluating service providers, especially, pay attention to the types of storage offered. Some offer only object storage, which is very different from block storage and file storage normally used in local data centers . Similarly, some vendors view databases as storage options, while others treat them as VMs.
Find out about the regional availability of cloud providers. The most important install datacenters around the world. If you have a legal or commercial obligation to keep your data in a specific country , it is extremely important that you choose the data centers in which your data will be hosted. It is also vital, in the event of a vendor outage, to ensure that your VMs do not automatically switch to data centers in unauthorized regions.
Carefully review the specific regional offerings of each cloud provider. Some use low-end servers in some areas. In addition, some operating systems or operating system features, such as encryption, may not be available in some areas due to regulation.
As you can see, the criteria to consider when evaluating cloud service providers are numerous. These are not all equal.