Basics

• EC2 is AZ resilient
• Instance Lifecycle : Running - Stopped - Terminated
• AMI contains
  • Permissions - Public , Owner Implicit Access, Explicit access to AWS accounts
  • Root Volume - OS
  • Block Device Mapping
• EC2 instance can have multiple network interfaces i.e. ENI. Each ENI can be in different Subnet as long as they are in same AZ
• Instances when stopped and started, they can be relocated to a different host. If the host has hardware failure they can be relocated to a different host.
• IF you restart an instances, it retains the host

Instance Metadata

• http://169.254.169.254/latest/meta-data
• Metadata service is not authenticated or encrypted

Launch Configurations & Launch Templates

• Define configurations of EC2 instances in advance.
• Example configurations are AMI, Instance Type, Storage, Key Pair, Networking Configuration, Security Groups, Userdata, IAM Role etc
• Both are not editable thought LT has versions
• LT allow more features like T2/T3 unlimited, Placement Groups, Capacity Reservations , Elastic Graphics
• While LC can be used for launching ASG, LT can be additionally used to launch EC2 instances from console or CLI