Pkl is a configuration language created by Apple (https://pkl-lang.org/index.html).
It is capable of serializing to other formats like YAML, so it's possible to
write a CloudFormation template with pkl. This repository hosts the cloudformation.pkl
package that can be imported into your projects to provide a type-safe authoring experience.
The package also has a set of high level patterns that you adapt for your own needs.
The following is a basic example of a pkl CloudFormation template.
AWSTemplateFormatVersion: String = "2010-09-09"
Description = "My template"
Parameters {
["Name"] {
["Type"] = "String"
}
}
Resources {
["MyBucket"] {
["Type"] = "AWS::S3::Bucket"
["Properties"] {
["BucketName"] {
["Ref"] = "Name"
}
}
}
}Running pkl eval -f yaml on this file results in the following:
AWSTemplateFormatVersion: 2010-09-09
Description: My template
Parameters:
Name:
Type: String
Resources:
MyBucket:
Type: AWS::S3::Bucket
Properties:
BucketName:
Ref: NameHere's an example of a file you could write using modules in the cloudformation.pkl package:
amends "@cfn/template.pkl"
import "@cfn/cloudformation.pkl" as cfn
import "@cfn/aws/s3/bucket.pkl" as bucket
Description = "Create a bucket"
Metadata {
["Foo"] = "bar"
}
Parameters {
["Name"] {
Type = "String"
Default = "baz"
}
}
Resources {
["TypedBucket"] = new bucket.Bucket {
BucketName = cfn.Ref("Name")
}
}Note that the package alias @cfn is enabled by creating a PklProject file that looks like this:
amends "pkl:Project"
dependencies {
["cfn"] {
uri = "package://pkg.pkl-lang.org/github.com/aws-cloudformation/cloudformation-pkl/cloudformation@0.1.5"
}
}In the directory where you create PklProject, run pkl project resolve, which will auto-generate the PklProject.deps.json file. Then you can run pkl eval my-template.pkl -f yaml and the @cfn package will be downloaded in order to generate the output.
It's possible to build higher level patterns in Pkl. In the following example,
we are building a VPC defined in patterns/vpc.pkl.
amends "@cfn/template.pkl"
import "@cfn/cloudformation.pkl" as cfn
import "@cfn/patterns/vpc.pkl"
local pub1 = new vpc.Subnet {
LogicalId = "Pub1"
IsPublic = true
Az = cfn.Select(0, cfn.GetAZs("us-east-1"))
Cidr = "10.0.0.0/18"
}
local pub2 = new vpc.Subnet {
LogicalId = "Pub2"
IsPublic = true
Az = cfn.Select(1, cfn.GetAZs("us-east-1"))
Cidr = "10.0.64.0/18"
}
local priv1 = new vpc.Subnet {
LogicalId = "Priv1"
IsPublic = false
Az = cfn.Select(0, cfn.GetAZs("us-east-1"))
Cidr = "10.0.128.0/18"
PublicNATGateway = pub1.natGateway
}
local priv2 = new vpc.Subnet {
LogicalId = "Priv2"
IsPublic = false
Az = cfn.Select(1, cfn.GetAZs("us-east-1"))
Cidr = "10.0.192.0/18"
PublicNATGateway = pub2.natGateway
}
local myvpc = new vpc {
LogicalId = "MyVPC"
Subnets {
pub1
priv1
pub2
priv2
}
}
Resources {
// Create the VPC
...myvpc.Resources
// Create other resources inside the VPC...
}
Outputs {
...myvpc.Outputs
}