Amazon EC2 pricing for dummies – Part 2: Storage costs

Update: Amazon now offers an improved cost calculator which is much easier to use.

In my last post I complained about Amazon EC2′s complicated pricing structure. Today, I will chat a little about my pricing experience with my own server. Before I continue I should say that my somewhat negative remarks about EC2 in recent articles don’t mean that I dislike Amazon’s cloud. On the contrary; I like Amazon almost as much as I am a MS fan boy. Cloud computing is still in its infancy, so it is only natural that things have to mature.

Okay, let’s start with Amazon’s Simple Monthly Calculator. When you open the page, you will recognize that Amazon S3 (storage) is the only service that is already checked. The reason why this service is often essential for other services is because you always need a place to store your data. Hence, you have to include it in your price calculation.

S3 is needed for EC2 if you want to bundle AMIs (store OS images). Thus, S3 is not really necessary to run an EC2 instance (virtual server), but I think most EC2 customers are using this feature. There are five different factors that determine your monthly S3 costs: storage (GB-months), data transfer-in, data transfer-out, PUT/LIST Requests, and other requests.

Amazon S3 costs

As far I can tell, all of these costs are more or less negligible in my case. I have been bundling quite a few AMIs in September because I was testing this feature. At the moment, I have about 10 different copies of my virtual server stored at S3. All in all, I paid $1.76 in September for this service. The $1.73 is for the storage usage, the rest for the other factors mentioned above. The S3 costs will probably drop below $1 in October because I will only keep the last three versions of my installation. Please note that only the system partition is bundled and stored to S3. This is why the amount of compressed data on S3 is only 11GB in my case. Since I am running Fedora without any graphical interface the virtual machine is relatively small. My system partition only occupies about 5GB. Of course, if you run a common Windows server on EC2, things look a bit different. It probably only makes sense to use Server Core in the cloud. Amazon charges $0.15 per GB-month in the U.S. for S3 storage. More info about S3 pricing can be found here.

Amazon EBS costs

Another factor are Elastic Block Store (EBS) costs. EBS is a part of the EC2 service and shouldn’t be confused with S3. S3 is only for storing OS images (when used with EC2) and EBS storage can be attached directly to a running EC2 instance. You can run an instance without renting EBS storage because each instance type comes with a system and data partition, which is already included in the EC2 instance fee (topic of my next post). My High-CPU Medium Instance comes with 350GB, which is more than enough for my purposes.

However, I am using EBS because I want to separate the MySQL database and the WordPress installation from the EC2 instance. An advantage is that I can take snapshots (backups) of the EBS volume with just a mouse click. This is much more convenient than bundling an image. Moreover, it allows me to launch a second instance, modify the OS, and then just attach the currently active EBS volume with the latest data (reader comments for example) to the new instance without interruption.

The extra costs for EBS are also negligible in my case. I paid 55 cents for EBS in September. My EBS volume has only 5GB, which is enough storage for more than 1,000 4sysops articles including all the screenshots. Of course, if you need more storage for your applications and you also want to separate the data storage from the instance, you will pay more. Amazon charges $0.10 per GB-month for EBS volumes. Pricing for EBS snapshots is comparable to S3 storage ($0.15 per GB-month).

So all in all I am paying not more than $2 per month for storage. 4sysops isn’t a big website, but it also isn’t small. Hence, if you plan to run a web server on EC2, you probably will have comparable storage costs. In my next post, I will discuss the decisive EC2 fees, i.e. bandwidth and instance costs.