Which Cloud is better?

In this post, I will talk about another question that I get asked often: “Which Cloud is Better?”. As with many things in life, there is no single or a simple answer to this question.

When you are looking to use a public cloud, you are looking at various aspects of the cloud. Some of them would include:

  • What services does the Cloud provide?
  • What will be the performance of my VMs?
  • What is the cost that I will incur?
  • How easy it is to migrate to this Cloud?
  • Will I be locked in with this vendor?

These are the basic minimum questions that will arise when you are choosing a Cloud provider. Against all of these, you will find that it is very difficult to do an Apple to Apple comparison between various Cloud providers.

Let us take performance for example. Assume you have the same configuration (say a 2 vCPU system with 4 GB RAM and 500GB hard disk) from two vendors, will the performance of your VM be the same in both places? We cannot answer this with any assurance because performance of a VM will depend on how over-provisioned the bare metal is and also on the noisy neighbors. Noisy neighbors are the other VMs which are running on the same bare metal your VM is running on and if any of the other VMs start consuming more of the resources, it can have an impact on the performance of your VM. We do not know how the Cloud provider places the VMs on Bare Metal and hence you cannot speak with confidence about performance of the VM. As you would have guessed, depending on the neighbors and when they consume resources, your performance will vary.

A recent blog from Google talks about this aspect and claims that Google has the best price performance. You can read the Google blog here.

One way of guaranteeing the performance would be to take a dedicated VM. This means only your VMs will run on the bare metal and no other VM will be placed on this bare metal. AWS has dedicated instance and Softlayer has Virtual Private instances. As you can expect, these options will give you a more reliable performance but at a higher cost.

This brings us to the cost comparison. The standard question I hear is ‘Which Cloud is cheaper?’. Once again this is not an easy question to answer and will depend on the workload you have and the services that you use. Let us take a very simple case in AWS. If you are using say a t2.micro instance with say 100GB disk as a web server, you cannot immediately calculate what will be your monthly outflow. You need to have an idea on the network traffic which goes out from your instance. AWS doesn’t charge for incoming traffic but outgoing traffic is charged. So the cost you incur will depend on the traffic. Or take the case of S3. It is not just about the cost of storing object. The no:of GET, POST, PUT etc requests also get charged. Hence computing the cost is not an exact science. You need to get some data before you can compute cost with some confidence.

Most people tend to compare the instance cost and decide on which is cheaper. We need to understand that instance/VM is just a small part of the larger equation. We have storage costs, I/O costs, networking costs, support cost and so on. Comparing only the VM costs does not give the big picture regarding costs at all.

Migration is a topic which requires a post of its own. I will write about it in the near future.