Amazon EC2 Upgrade

Question

We are considering upgrading from an t2.micro AWS server instance to a m3.medium instance based on the recommendation here and some research offline. We feel the need to upgrade primarily for speed issues and to ensure google bots crawl our fast growing site fast enough. We have upward of 8000 products (on magento) and that will grow.

While trying to understand what exactly could be the constraint of the current t2.micro instance, we ran through a lot of logs but couldn't find anything specific that could indicate a bottle-neck as such in the current usage.

Could anyone help point out 1. What are the clues that can be found in logs which could show potential bottleneck issues(if-any) with the current t2.micro instance 2. How could we find out if google-bot had issues while crawling and stopped crawling due to server performance related issues.

Answer 1

There are two things to note about t2.micro instances:

• They have CPU limitations based upon a CPU credits system
• They have limited network bandwidth

CPU credits

The T2 family is very powerful (see comparison between t2.medium and m3.medium ), but there is a limit on the amount of CPU that can be used.

From the T2 documentation :

Each T2 instance starts with a healthy initial CPU credit balance and then continuously (at a millisecond-level resolution) receives a set rate of CPU credits per hour, depending on instance size. The accounting process for whether credits are accumulated or spent also happens at a millisecond-level resolution , so you don't have to worry about overspending CPU credits; a short burst of CPU takes a small fraction of a CPU credit.

Therefore, you should look at the CloudWatch CPUCreditBalance metric for the instance to determine whether it has consumed all available credits. If so, then the CPU will be limited to 10% of the time and you either need a larger T2 instance, or you should move away from the T2 family.

In general, T2 instances are great for bursty workloads, where the CPU only spikes at certain times. It is not good for sustained workloads.

Network Bandwidth

Each Amazon EC2 instance type has a limited amount of network bandwidth. This is done to prevent noisy neighbour situations. While AWS only describes bandwidth as Low/Moderate/High, there are some better details at: EC2 Instance Types's EXACT Network Performance?

You can monitor network traffic of your EC2 instances using CloudWatch . Pay attention to NetworkIn and NetworkOut to determine whether the instances are hitting limits.