EC2, a Virtual Machine in the cloud on which you have OS-level control. You can run this cloud server whenever you want and can be used when you need to deploy your own servers in the cloud, similar to your on-premises servers, and when you want to have full control over the choice of hardware and the updates on the machine

Elastic Transcoder is an AWS Service Tool that helps you in changing a video’s format and resolution to support various devices like tablets, smartphones, and laptops of different resolutions.

Different types of Cloud Services are:

• Software as a Service (SaaS)
• Data as a Service (DaaS)
• Platform as a Service (PaaS)
• Infrastructure as a Service (IaaS)

When you create an instance in AWS, you may or may not want that instance to be accessible from the public network. Moreover, you may want that instance to be accessible from some networks and not from others.
Security Groups are a type of rule-based Virtual Firewall using which you can control access to your instances. You can create rules defining the Port Numbers, Networks, or protocols from which you want to allow access or deny access.

• When AWS creates EC2 instances, there are some blocks of computing capacity and processing power left unused. AWS releases these blocks as Spot Instances. Spot Instances run whenever capacity is available.These are a good option if you are flexible about when your applications can run and if your applications can be interrupted.
• On the other hand, On-Demand Instances can be created as and when needed. The prices of such instances are static. Such instances will always be available unless you explicitly terminate them.

Key-Pairs are secure login information for your Virtual Machines. To connect to the instances, you can use Key-Pairs which contain a Public Key and a Private Key.

• Connection Draining is a feature provided by AWS which enables your servers which are either going to be updated or removed, to serve the current requests.
• If Connection Draining is enabled, the Load Balancer will allow an outgoing instance to complete the current requests for a specific period but will not send any new request to it. Without Connection Draining, an outgoing instance will immediately go off and the requests pending on that instance will error out.

• A Stateful Firewall is the one that maintains the state of the rules defined. It requires you to define only inbound rules. Based on the inbound rules defined, it automatically allows the outbound traffic to flow. 
• On the other hand, a Stateless Firewall requires you to explicitly define rules for inbound as well as outbound traffic. 
• For example, if you allow inbound traffic from Port 80, a Stateful Firewall will allow outbound traffic to Port 80, but a Stateless Firewall will not do so.

T2 Instances are designed to provide moderate baseline performance and the capability to burst to higher performance as required by the workload.

DNS and Load Balancer are a part of IaaS-Storage Cloud Service.