Regions and Availability Zones

From Amazon Elastic Compute Cloud: 2009-03-01

previous page next page

Regions and Availability Zones

Amazon EC2 provides the ability to place instances in multiple locations. Amazon EC2 locations are composed of Availability Zones and regions. Regions are dispersed and located in separate geographic areas (e.g., US and EU). Availability Zones are distinct locations within a region that are engineered to be insulated from failures in other Availability Zones and provide inexpensive, low latency network connectivity to other Availability Zones in the same region.

By launching instance in separate regions, you can design your application to be closer to specific customers or to meet legal or other requirements. By launching instances in separate Availability Zones, you can protect your applications from the failure of a single location.

The following graphic shows the Amazon EC2 cloud. Each region is completely independent. Each Availability Zone is isolated, but connected through low-latency links.

Regions

Amazon EC2 provides multiple regions so you can launch Amazon EC2 instances in locations that meet your requirements. For example, you might want to launch instances in Europe to be closer to your European customers or to meet legal requirements.

Each Amazon EC2 region is designed to be completely isolated from the other Amazon EC2 regions. This achieves the greatest possible failure independence and stability, and it makes the locality of each EC2 resource unambiguous.

To launch or work with instances, you must specify the correct regional URL endpoint. For example, to access the United States region, you make service calls to the us-east-1.ec2.amazonaws.com service endpoint. To access the region in Europe, you make service calls to the eu-west-1.ec2.amazonaws.com service endpoint.

Example

This shows an example of describing the Availability Zones within the EU region.

ec2-describe-availability-zones --region eu-west-1
AVAILABILITYZONE        eu-west-1a      available       eu-west-1
AVAILABILITYZONE        eu-west-1b      available       eu-west-1

Region Selection

This section describes how to find available regions and how to select one.

To view the available regions

Enter the following command:

PROMPT> ec2-describe-regions

REGION        us-east-1        us-east-1.ec2.amazonaws.com
REGION        eu-west-1        eu-west-1.ec2.amazonaws.com

Note

Data transfer between regions is charged at the Internet data transfer rate for both the sending and the receiving region. For detailed information on Amazon EC2 charges, go to the Amazon EC2 Product Page.

The us-east-1.ec2.amazonaws.com region is the original Amazon EC2 region and is selected by default.

To select a specific region using the command line tools

Change the EC2_URL environment variable.

	Note
	You can also use the `--region` command line option, or override the URL endpoint using the `-U` flag.

To select a specific region for Query or SOAP

Configure your application to use the appropriate service endpoint.

Availability Zones

Amazon operates state-of-the-art, highly available data center facilities. However, failures can occur that affect the availability of instances that are in the same location. Although this is rare, if you host all your Amazon EC2 instances in a single location that is affected by such a failure, your instances will be unavailable.

For example, if you have instances distributed across three Availability Zones and one of them fails, you can design your application so the instances in the remaining Availability Zones handle any requests.

	Note
	You can use Availability Zones in conjunction with elastic IP addresses to remap IP addresses across Availability Zones. For information on elastic IP addresses, see Elastic IP Addresses.

Availability Zone Selection

When you launch an instance, you can optionally specify an Availability Zone. If you do not specify an Availability Zone, Amazon EC2 selects one for you in the region that you are using. When launching your initial instances, we recommend accepting the default Availability Zone, which allows Amazon EC2 to select the best Availability Zone for you based on system health and available capacity. Even if you have other instances running, you might consider not specifying an Availability Zone if your new instances do not need to be close to, or separated from, your existing instances.

To view the Availability Zones available to you

Enter the following command:

PROMPT> ec2-describe-availability-zones
AVAILABILITYZONE        us-east-1a      available
AVAILABILITYZONE        us-east-1b      available
AVAILABILITYZONE        us-east-1c      available

	Note
	Availability Zones are not the same across accounts. The Availability Zone us-east-1a for account A is not necessarily the same as us-east-1a for account B. Zone assignments are mapped independently for each account.

After determining the Availability Zones that are available to you, you can launch instances in any of the zones.

	Note
	You are charged a small bandwidth charge for data that crosses Availability Zones. For more information, go to the Amazon EC2 product page.

Resources

The following table describes which Amazon EC2 resources are global, regional, or Availability Zone-based.

Resource	Type	Description
`AWS Account`	Global	You use the same AWS account in all regions.
`DevPay Product Codes`	Global	You use the same DevPay product codes throughout all regions.
`Amazon EC2 System Identifiers`	Regional	Includes the AMI ID, Instance ID, EBS Volume ID, EBS Snapshot ID, and so on.
`Instances`	Availability Zone	Instances are tied to Availability Zones. However, the instance ID is tied to the region.
`AMIs`	Regional	AMIs are tied to the region where its files are located within Amazon S3.
`Security Groups`	Regional	Security groups are not copied across regions. Instances within the region cannot communicate with instances outside the region using group-based firewall rules. Traffic from instances in another region is seen as WAN bandwidth.
`SSH Key Pairs`	Regional	Key pairs (to connect to instances) are region-specific.
`User-Supplied Identifiers`	Regional	Includes security group names, SSH key pair names, and so on. Although you can create the same names in multiple regions, they have no relationship to each other.
`Elastic IP Addresses`	Regional	Elastic IP addresses are tied to a region and cannot be mapped across regions.
`EBS Volumes`	Availability Zone	An Amazon EBS volume must be located within the same Availability Zone as the instance to which it attaches.
`EBS Snapshots`	Regional	Snapshots are tied to regions and can only be used for volumes within the same region.

previous page start next page