AWS CloudFormation Intrinsic Functions and Mappings

AWS CloudFormation
Intrinsic Functions and Mappings
Managing Windows instances in the Cloud

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CloudFormation Deep Dive

CloudFormation Review
AWS CloudFormation Allows you to build Infrastructure as
code using templates which are constructed from json.

CloudFormation Template
There are 8 sections of a Cloud formation template, most
of which are optional
Format Version
(optional)
Description (optional)
Metadata (optional)
Mappings (optional)
Parameters(optional)
Conditions(optional)
Resources (required)
Outputs(optional)

CloudFormation
Best Practice
For more info
http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/best-practices.html
As you use Cloud Formation make sure you follow the best
practices for success
• Do Not Embed Credentials in You Templates
• Use AWS-Specific Parameter Types
• Use Parameter Constraints
• Validate Templates Before Using them
• Manage All Stack Resources Through AWS Cloud Formation

CloudFormation
Intrinsic Functions
Function Overview
Fn::Base64 returns the Base64 representation of the input string (user data)
Fn::FindInMap returns the value corresponding to keys in a two-level map that is
declared in the Mappings section
Fn::GetAtt returns the value of an attribute from a resource in the template.
Fn::GetAZs returns an array that lists Availability Zones for a specified region.
Fn::Join appends a set of values into a single value, separated by the
specified delimiter.
Fn::Select returns a single object from a list of objects by index.
Ref returns the value of the specified parameter or resource.

CloudFormation
Mappings
The Mappings section is optional but is matches a
key to a corresponding set of named values.
If you want to set values based on region, you can
create a mapping that uses the key as the name and
then contains the values you want to specify for each
region.
You cannot include parameters, pseudo parameters, or intrinsic
functions in the Mappings section.

CloudFormation
Mappings - cont.
"Mappings" : {
"RegionMap" : {
"us-east-1" : { "32" : "ami-6411e20d"},
"us-west-1" : { "32" : "ami-c9c7978c"},
"eu-west-1" : { "32" : "ami-37c2f643"},
"ap-southeast-1" : { "32" : "ami-66f28c34"},
"ap-northeast-1" : { "32" : "ami-9c03a89d"}
}
}

CloudFormation
Mappings - cont.
"asgApp": {
"MinSize" : { "value": "2" },
"MaxSize" : { "value": "2" },
"DesiredCapacity" : { "value": "2" },
"HealthCheckType" : { "value": "EC2" },
"TerminationPolicies" : { "value":
"OldestInstance" }
}

CloudFormation
Mappings - cont.
"asgAppA": {
"Type": "AWS::AutoScaling::AutoScalingGroup",
"Properties": {
"AvailabilityZones" : { "Ref": "AZs" },
"VPCZoneIdentifier" : { "Ref": "PrivateAPPSubnets" },
"LaunchConfigurationName" : { "Ref": "LaunchConfig" },
"MinSize" : { "Fn::FindInMap": [ "asgApp",
"MinSize", "value" ] },
"MaxSize" : { "Fn::FindInMap": [ "asgApp",
"MaxSize", "value" ] },
"DesiredCapacity" : { "Fn::FindInMap": [ "asgApp",
"DesiredCapacity", "value" ] },
"HealthCheckType" : { "Fn::FindInMap": [ "asgApp",
"HealthCheckType", "value" ] },
"TerminationPolicies" : [{ "Fn::FindInMap": [ "asgApp",
"TerminationPolicies", "value" ] }],

Fn::FindInMap
"Resources" : {
"myEC2Instance" : {
"Type" : "AWS::EC2::Instance",
"Properties" : {
"ImageId" : { "Fn::FindInMap" : [ "RegionMap", { "Ref" :
"AWS::Region" }, "32"]},
"InstanceType" : "m1.small" }
}
}
}
This function performs lookups, it accepts a ‘mappings’ object on of
one or two keys and then returns a value
For more info
http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-
reference-findinmap.html

Fn::Base64
{ "Fn::Base64" : ”apt-get update –y " }
This function accepts plain text and converts it to Base 64
For more info
reference-base64.html

Fn::Join
"Outputs" : {
"URL" : {
"Description" : "The URL of your demo website",
"Value" : { "Fn::Join" : [ "", [ "http://", { "Fn::GetAtt" : [
"ElasticLoadBalancer", "DNSName" ]}]]}
}
}
This can be used to concatenate various components to produce
things such as a URL.
For more info
reference-join.html

Fn::GetAtt
Some examples of attributes that can be called are:
• EC2 -> PrivateIp
• EC2-> PublicIp
• ElasticLoadBalancing -> DNSName
• IAM::Group -> ARN
• S3 Bucket -> DomainName
• Simple AD -> Alias
As you dynamically create items in your Cloud Formation templates ,
you may need to use some of the Attributes after they are created.
For more info
reference-getatt.html

Fn::GetAtt
"MyEIP" : {
"Type" : "AWS::EC2::EIP",
"Properties" : {
"InstanceId" : { "Ref" : "MyEC2Instance" }
}
}
“Fn:GetAtt” :[ “MyEIP”, “AllocationId” ]
As you dynamically create items in your Cloud Formation templates
For more info
reference-getatt.html

Fn::GetAZs
{ "Fn::GetAZs" : "us-east-1" }
{ "Fn::GetAZs" : { "Ref" : "AWS::Region" } }
The intrinsic function Ref returns to value of the specified
parameter or resource.
For more info
reference-select.html
NOTE: You can use the Ref function in the Fn::GetAZz function.

Fn::Select
{ “Fn::Select” : [ “0”, {”Fn::GetAZs” : “”} ] }
Selects a single object from a list of object and can be paired with
other functions such as Fn::GetAZs
For more info
reference-select.html
The output is the first Availablity zone in the region where the
template is applied.
Replacing the 0 with a 1 would select the second Availability Zone

Fn::Ref
"MyEIP" : {
"Type" : "AWS::EC2::EIP",
"Properties" : {
"InstanceId" : { "Ref" : "MyEC2Instance" }
}
}
The intrinsic function Ref returns to value of the specified
parameter or resource.
For more info
reference-ref.html

Cloud Formation Templates
Real World Examples
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of Stephen Radford via
http://snap.io

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AWS CloudFormation Intrinsic Functions and Mappings

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