Q: What is EC2?

A: EC2 is an Infrastructure as a Service Cloud Computing Platform provided by Amazon Web Services, that allows users to instantiate various types of virtual machines.

Q: What is an instance?

A: An EC2 instance is a Virtual Machine running on Amazon's EC2 Cloud.

Q: What is an AMI?

A: An AMI (Amazon Machine Image) is a preconfigured bootable machine image, that allows one to instantiate an EC2 instance. (EC2 Virtual Machine)

Q: What is an AKI?

A: An AKI (Amazon Kernel Image) is a preconfigured bootable kernel miniimage, that are prebuild and provided by Amazon to boot instances. Typically one will use an AKI that contains pv-grub so that one can instantiate an instance from an AMI that contains it's own Xen DomU kernel that is managed by the user.

Q: What is EBS?

A: EBS stands for Elastic Block Storage, and is a service that provides dynamically allocatable, persistent, block storage volumes that can be attached to EC2 instances. Most system operations that can be performed with a HDD can be performed with an EBS volume. e.g. - formatted with a filesystem and mounted. EBS also provides additional SAN-like features such as taking snapshots of volumes, and detaching and reattaching volumes dynamically.

Q: What is the difference between an instance-store AMI/instance and an EBS AMI/instance?

A: An instance-store instances boot off of an AMI that instantiates a non-persistent root volume that loses all data on poweroff, or hardware failure. EBS instances boot off an AMI that consists of an EBS volume that persists after powering off (stopping) an instance or in the event of a hardware failure a given instance is running on.

Q: What is the difference between an terminating an instance and stopping an instance?

A: Please note this difference is only applicable to EBS-root instances. When one stops an instance it basically virtually powers off the instance but it remains in the inventory to be powered on (started) again. Terminating an instance removes its records from the system inventory and usually also deletes its root volume.

Q: How does IP addressing work in EC2?

A: In "classic EC2" each instance is given a randomly assigned private IP address that maps via NAT to an also randomly assigned public IP address. VPC instances allow more control of the private (and public) IP address mappings and assignment, and as such let one assign custom private IP ranges and addresses, in addition to having the option to not assign public IP address mappings.

Q: What is an Elastic IP Address (EIP)?

A: An Elastic IP address is a Public IP addressed that is assigned to an individual AWS account. These IPs are assigned by region. This address can be assigned to any EC2 instance within a region and will replace the regularly assigned random public IP address.

Q: What is an EC2 Region?

A: An EC2 Region refers to a geographic region that is a completely autonomous set of compute resources, with their own management infrastructure. Regions do not share any resources, so they are considered completely seperate for disaster recovery purposes.

Q: What EC2 Regions are there?

A: us-east-1 (Virginia), us-west-1 (N. California), us-west-2 (Oregon), eu-west-1 (Ireland), ap-southeast-1 (Singapore), ap-northeast-1 (Tokyo), ap-southeast-2 (Sydney), sa-east-1 (Sao Paulo)

Q: What is an EC2 Availability Zone?

A: An availability zone is a separate "failure zone" within a given region that can have resources instantiated in. Each region has it's own power grid, and physical set of hardware and resources. Availability zones within a given region have a shared management interface/infrastructure.

Q: What is an EC2 Security Group?

A: A Security Group (SG) is a management construct within EC2 that acts similarily to a network based firewall. An instance must be assigned one or more security groups at first instantiation. Security group membership may not change after initial instantiation. Security groups allow one to set incoming network rules allowing certain TCP/UDP/ICMP protocols ingress via rules based on incoming security group ID, network address or IP address. Security groups do not restrict outbound traffic.