Friday, March 6, 2015

About EC2 and purchase options in EC2

EC2 (Elastic Cloud Compute):
Can host the Unix and Windows based operating system.

Since its running inside the cloud environment no need of purchasing any server or software.

We are going to focus on Linux Instances.

Purchase options for EC2:

1. Spot Instances:Bid on usused EC2 instances and can be bought in at lower price than the normal instance price options. But tradeoff here is they are not guaranteed compute time and amazon can take back the instance anytime it requires it. So it is only suitable for the batch processeses.

2. Reserved Instances: It allows to purchase and pay initially at lower price for annually and is best suited when you are confirm that you will be running the server for a definite period like 24 x 7. We purchase instance in a specific in a specific availaibility zone. Purchasing Instances help us to pay lower price/hour for annual cost or 3 years cost and also guarantee us the availaibility and access to the instances. If  that availaibility zone goes down and your instances spin up from different availaibility zone than as you have guaranteed access so you will have priority over the on demand instances and instances will be first allocated to you since you have reserved them initially.

3. On Demand Instances:On Demand instances are the regular instances priced at per hour there is no upfront costs. Depending on the size of the instances you are using like micro, small , medium , large for e.g. micro instances are very cheap and increases as you increase the size.

So the best combination is always a combination of the Reserved Instances and the on demand instances.

Practical Scenario:- Consider a scenario were we acknowledge that we need 2 high availaible instances which we will be running all the time so we will purchase 2 highly available instances and lets say we consider scenarios of load and needs 2 more instances in such case than we will buy 2 more reserve instances with medium availaibility say 50% and just in case the load further increases we will consider using on demand instances.

Amazon limits the number of instances that the account can have by default. So by default we can only have 20 instances at starting. Also by default we are only allowed 5 elastic ip addresses. However we can simply increase that by filling up the form at the http://aws.amazon.com and usually they increase the instances to the requested amount within 24 to 48 hours, all you need to explain why you need them and they will do it for you. 


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