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
AWS 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 specifyingAWS::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.