AWS Questions and Answers

Omkar Tirodkar

Omkar Tirodkar

25 January 2019

Here, You will find the most important AWS questions and answers explained in detail.

What is an AWS region?

An AWS Region represents a geographical location with a collection of availability zones mapped to the physical data centers in that region. Every region is physically isolated from each other. Each region is independent of every other region in terms of location, power, water supply, etc. The greatest possible fault tolerance and stability is achieved by this. This level of isolation is useful for workloads with compliance and data sovereignty requirements. AWS ensures that data do not leave a particular geographic region. The presence of AWS regions worldwide is also important for workloads that need low latency and need to be located near users in a particular geographic area. Each region has two or more availability zones with each zone hosted in separate data centers from another zone. Each Availability Zone is isolated, but the Availability Zones in a region are connected via low-latency links. The following table lists the details of the regions provided by an AWS account.

Region CodeRegion Name
us-east-1US East (N. Virginia)
us-east-2US East (Ohio)
us-west-1US West (N. California)
us-west-2US West (Oregon)
ca-central-1Canada (Central)
eu-central-1EU (Frankfurt)
eu-west-1EU (Ireland)
eu-west-2EU (London)
eu-west-3EU (Paris)
eu-north-1EU (Stockholm)
ap-northeast-1Asia Pacific (Tokyo)
ap-northeast-2Asia Pacific (Seoul)
ap-northeast-3Asia Pacific (Osaka-Local)
ap-southeast-1Asia Pacific (Singapore)
ap-southeast-2Asia Pacific (Sydney)
ap-south-1Asia Pacific (Mumbai)
sa-east-1South America (São Paulo)

Does AWS have the option for vertical auto-scaling of EC2 instance?

AWS does not support vertical auto-scaling. But it can be achieved in another way. In order to scale the EC2 instance vertically we need to perform the following steps:

  • Stop EC2 instance.
  • Change the EC2 instance type.
  • Restart the EC2 instance.

We can automate this process using the AWS lambda functions. We can integrate the lambda function with the Cloudwatch. Then we can invoke lambda function based on the Cloudwatch metrics of an EC2 instance (e. g. Trigger lambda function if CPU utilization of EC2 instance is greater than 80%) Note: This approach of vertical scaling causes some downtime of EC2 instance.

What is T2 T3 unlimited in AWS?

A burstable performance instance, when configured as unlimited, can sustain high CPU performance for any period of time whenever required. The instance price automatically covers all sudden spikes in usage if the average CPU utilization of the instance is at or below the baseline over a rolling 24-hour time period or the instance lifetime, whichever is shorter. If the instance is running at higher CPU utilization for a prolonged period, it can do so for a flat additional rate per vCPU-hour. The unlimited mode credit configuration option for burstable performance instances can be enabled or disabled at any time for running or stopped instance.

  • T3 instances are launched as unlimited by default.
  • T2 instances are launched as a standard by default. We can convert them into unlimited burstable instances.

How Unlimited Burstable Performance Instances Work?

Burstable performance instance earns credits if the instance is at or below the baseline CPU utilization. (For example, a t3.nano instance, can earn a maximum of 144 credits in a 24-hour period). If it runs below the CPU utilization beyond a period of 24 hrs, it doesn’t earn additional credits. These credits can be spent when the CPU utilization of the instance is above the baseline. If a burstable performance instance configured as unlimited consumes its CPU credit balance, it can spend surplus credits to burst beyond the baseline. When its CPU utilization decreases below the baseline, it uses the CPU credits that it earns to pay the surplus credits that spent earlier. The ability to earn CPU credits to pay down surplus credits helps Amazon EC2 to average the CPU utilization of an instance over a 24-hour period. However, if the CPU utilization stays above the baseline and the CPU Surplus Credit Balance value reaches its maximum limit (the maximum a t3. Nano instance, can earn in a 24-hour period, i.e. 144 credits). The surplus credits spent beyond that limit will result in a small additional charge per hour for the instance.

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