Fn::GetAZs - Amazon CloudFormation
DeclarationParametersReturn valueExamplesSupported functions
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Fn::GetAZs

The intrinsic function Fn::GetAZs returns an array that lists Availability Zones for a specified Region in alphabetical order. Because customers have access to different Availability Zones, the intrinsic function Fn::GetAZs enables template authors to write templates that adapt to the calling user's access. That way you don't have to hard-code a full list of Availability Zones for a specified Region.

Important

The Fn::GetAZs function returns only Availability Zones that have a default subnet unless none of the Availability Zones has a default subnet; in that case, all Availability Zones are returned.

Similarly to the response from the describe-availability-zones Amazon CLI command, the order of the results from the Fn::GetAZs function isn't guaranteed and can change when new Availability Zones are added.

IAM permissions

The permissions that you need in order to use the Fn::GetAZs function depend on the platform in which you're launching Amazon EC2 instances. For both platforms, you need permissions to the Amazon EC2 DescribeAvailabilityZones and DescribeAccountAttributes actions. For EC2-VPC, you also need permissions to the Amazon EC2 DescribeSubnets action.

Declaration

JSON

{ "Fn::GetAZs" : "region" }

YAML

Syntax for the full function name:

Fn::GetAZs: region

Syntax for the short form:

!GetAZs region

Parameters

region

The name of the Region for which you want to get the Availability Zones.

You can use the AWS::Region pseudo parameter to specify the Region in which the stack is created. Specifying an empty string is equivalent to specifying AWS::Region.

Return value

The list of Availability Zones for the Region.

Examples

Evaluate a Region

For these examples, CloudFormation evaluates Fn::GetAZs to the following array—assuming that the user has created the stack in the us-east-1 Region:

[ "us-east-1a", "us-east-1b", "us-east-1c", "us-east-1d" ]

JSON

{ "Fn::GetAZs" : "" }
{ "Fn::GetAZs" : { "Ref" : "AWS::Region" } }
{ "Fn::GetAZs" : "us-east-1" }

YAML

Fn::GetAZs: ""
Fn::GetAZs:
  Ref: "AWS::Region"
Fn::GetAZs: us-east-1

 

Specify a subnet's Availability Zone

The following example uses Fn::GetAZs to specify a subnet's Availability Zone:

JSON

"mySubnet" : {
  "Type" : "AWS::EC2::Subnet",
  "Properties" : {
    "VpcId" : { 
      "Ref" : "VPC"   
    },
    "CidrBlock" : "10.0.0.0/24",
    "AvailabilityZone" : {
      "Fn::Select" : [ 
        0, 
        { 
          "Fn::GetAZs" : "" 
        } 
      ]
    }
  }
}

YAML

mySubnet: 
  Type: "AWS::EC2::Subnet"
  Properties: 
    VpcId: 
      !Ref VPC
    CidrBlock: 10.0.0.0/24
    AvailabilityZone: 
      Fn::Select: 
        - 0
        - Fn::GetAZs: ""

 

Nested functions with short form YAML

The following examples show valid patterns for using nested intrinsic functions using short form YAML. You can't nest short form functions consecutively, so a pattern like !GetAZs !Ref isn't valid.

YAML

AvailabilityZone: !Select
  - 0
  - !GetAZs
    Ref: 'AWS::Region'

YAML

AvailabilityZone: !Select
  - 0
  - Fn::GetAZs: !Ref 'AWS::Region'

Supported functions

You can use the Ref function in the Fn::GetAZs function.