Amazon EC2 Concepts
Internal
Overview
There are two Amazon Elastic Compute Cloud (EC2) platforms: EC2-VPC and EC2-Classic. EC2-VPC is aimed at launching AWS resources into a virtual private cloud (VPC). Also see Determining Whether You Are Using the EC2-VPC or EC2-Classic Platform.
Security Concepts
AMI (Amazon Machine Image)
An Amazon machine image is a template that contains a software configuration (operating system, application server, application).
To browse through available AMIs go to the EC2 console -> Left Navigation Pane -> AMIs.
AMIs can be chosen based on region, operating system, architecture (32-bit or 64-bit), launch permissions and storage for root device.
AMI ID
AMI Name
Must be unique within account and region.
AMI Storage for Root Device
An AMI can be either backed by Amazon EBS or backed by instance state. Backed by Amazon EBS mens that the root device for the instance launched from the AMI is an Amazon EBS volume, created from an Amazon EBS snapshot. Backed by instance state means that the root device is an instance store volume created from a template stored in Amazon S3. For more details: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ComponentsAMIs.html#storage-for-the-root-device
AMI Operations
Instance
From an AMI, you can launch an instance, which is a copy of the AMI running as a virtual server on a host computer in Amazon's data center. You can launch multiple instances from an AMI. An instance can be accessed using its public DNS name or public IP address. The DNS name follows the following pattern: ec2-<public_ip>.<region_code>.compute.amazonaws.com. An instance keeps running until it is explicitly stopped or until they fail. You can start from an existing AMI, log onto the instance, customize it with additional settings and software, and then save this customized image as a new AMI.
Instance Type
Each instance type offers different compute, memory, and storage capabilities and are grouped in instance families based on these capabilities. An example of instance type is t2.micro.
External Documentation:
- http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instance-types.html
- Instance Type Description (contains Instance Types Matrix) http://aws.amazon.com/ec2/instance-types/
- How many instances can I run? http://aws.amazon.com/ec2/faqs/#How_many_instances_can_I_run_in_Amazon_EC2
Instance Metadata and User Data
Networking
An instance specifies its networking by declaring a list of network interfaces. An example of how to specify networking as a CloudFormation resource is available here:
Subnet
Elastic IP and EC2 Instances
- An EC2 instance cannot be reached over ssh, even if it has an Elastic IP (public) address configured on it, if the subnet has no internet gateway associated with it (no 0.0.0.0/0 route to an internet gateway)
Security Groups
It seems that a security group must be associated with the instance, even if it allows 0.0.0.0/0. In the case no security group was deployed, the instance could not have been accessed - maybe it was a different type of transient failure, but it seems that it's a good idea to stand up a security group anyway.
Auto-Scaling
Load Balancing
Key Pair
An EC2 instance needs the name of a pre-existing key pair to secure ssh access to itself. A key pair is region-based.
Key Pair Operations
It does. not seem to be a way to created key pairs with CloudFormation.