AWS Availability Zones

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Availability Zones are distinct locations within an AWS Region engineered to be isolated from failures in other Availability Zones. They provide inexpensive, low-latency network connectivity to different Availability Zones in the same AWS Region. Each Region is entirely independent. To make the best use of Availability Zones, you need to understand how they work. This post will cover the basics of Availability Zones and Regions and how to use them to build highly available applications.

• Each Region has many availability zones (usually 3, the minimum is 2, maximum is 6). For Example:
– ap-southeast-2a
– ap-southeast-2b
– ap-southeast-2c
• Each availability zone (AZ) is one or more discrete data centers with redundant power, networking, and connectivity
• They’re separate from each other so that they’re isolated from disasters
• They’re connected with high bandwidth, ultra-low latency networking

AZ Benefits

In general, AWS Availability Zones allow you to launch production apps and highly available resources, resilient/fault-tolerant and scalable compared to a single data center. Having more options and backups is more practical. Lower latency where multiple availability zones are used makes sense to have the servers that provide a given application located relatively close to the end users that will access that application.

Azure And AWS AZs

AWS and Azure use Availability Zones (AZs) to provide high availability. An AZ is a data center that is physically isolated from other AZs. Each AZ comprises one or more data centers equipped with independent power, cooling, and networking. The goal of an AZ is to provide a high degree of availability for a given region. In Microsoft Azure, an Availability Zone is a physical location within an Azure region. Each Azure Region comprises multiple isolated areas known as Availability Zones. An Availability Zone shall consist of one or more data centers equipped with independent power, cooling, and networking. The goal of an Availability Zone is to provide a high degree of availability for a given region. In AWS, an Availability Zone is a physical location within an AWS Region. Each AWS Region comprises multiple isolated areas known as Availability Zones. An Availability Zone shall consist of one or more data centers equipped with independent power, cooling, and networking. The goal of an Availability Zone is to provide a high degree of availability for a given region.

AWS AZs

Availability Zones
Each Region has multiple isolated locations known as Availability Zones. The code for Availability Zone is its Region code followed by a letter identifier. For example, us-east-1a.

When you launch an instance, you select a Region and a virtual private cloud (VPC), and then you can select a subnet from one of the Availability Zones or let us choose one for you. If you distribute your instances across multiple Availability Zones and one instance fails, you can design your application so that an instance in another Availability Zone can handle requests. You can also use Elastic IP addresses to mask the failure of an instance in one Availability Zone by rapidly remapping the address to an instance in another Availability Zone.

The following diagram illustrates multiple Availability Zones in an AWS Region. Availability Zone A and Availability Zone B each have one subnet, and each subnet has instances. Availability Zone C has no subnets. Therefore you can’t launch instances into this Availability Zone.

As Availability Zones grow over time, the ability to expand them can become constrained. If this happens, we might restrict you from launching an instance in a constrained Availability Zone unless you already have an instance in that Availability Zone. Eventually, we might also remove the constrained Availability Zone from the list of Availability Zones for new accounts. Therefore, your account might have a different number of available Availability Zones in a Region than another account.

Describing An AZ

You can use the Amazon EC2 console or the command line interface to determine which Availability Zones are available for your account. For more information about these command line interfaces, see Access Amazon EC2.

To find your Availability Zones use the console.

Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/

From the navigation bar, choose the Regions selector and select the Region.

On the navigation pane, choose EC2 Dashboard.

The Availability Zones are listed in the Service health pane.

To find your Availability Zones using the AWS CLI.

Use the describe-availability-zones command to describe the Availability Zones within the specified Region enabled for your account.

aws ec2 describe-availability-zones --region region-name

Use the describe-availability-zones command to describe the Availability Zones regardless of the opt-in status.

aws ec2 describe-availability-zones --all-availability-zones
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