[AWS Architect] (31) EC2 Basics

Elastic Compute Cloud (EC2) provides scalable virtual servers (known as instances) in the cloud on-demand.

EC2 Features

  • EC2 Instances are grouped into families, which are designed for a specific broad type workload.
  • A security group must be assigned to an instance during the creation process.
  • Each instance must be placed into a VPC, an AZ, and a subnet.
  • Custom launch command (bootstrapping) can be passed into the instance via “user-data
  • Encrypted key-pairs are used to manage login authentication.
  • You are not billed if an instance is in a state of pending, stopping, stopped, shutting down, or terminated. EBD volumes incur charges regardless of the instance’s state.
  • AWS initially used a modified version of the Xen Hypervisor to host EC2 and then switched to Amazon’s own hypervisor Nitro.
  • EC2 Instance Role is an IAM role that can be assumed by an EC2 instance. An Instance Profile, which is a container for the roles, allows application on the EC2 instances to access the temporary credentials using the instance metadata.


  • Bootstrapping is a process where instructions are executed on an instance during its launch process.
  • User Data can be used to run shell scripts (Bash or PowerShell) or run cloud-init directives.

Private or Public Instances

  • Private Instances
    • Private IP is automatically allocated when an instance is launched and is used for internal communication.
    • Allocated with ip-x.x.x.x.ec2.internal DNS name – only works inside AWS.
    • The private IP and the domain name are unchanged during stop/starts – released when terminated.
  • Public Instances
    • A public IP is allocated when the machine starts and deallocated when it stops.
    • A Public IPs is auto-assigned based on the subnet settings. But you can assign a public IP to an instance during the launch process.
    • Elastic IP (EIP) can be allocated. It is a static IPv4 address and is not deallocated when the instance stops.

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