cloudformation-extensions
v0.0.3
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Extensions to Amazon CloudFormation
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cloudformation-extensions
Extensions to Amazon's CloudFormation Template JSON format.
Installation
Use the Docker Container (recommended)
docker run -v .:/cfnex joshbalfour/cfnex -i /cfnex/{inFile} -o /cfnex/{outFile}
(mapping the current directory to /cfnex in the container)
or grab from NPM
npm install -g cloudformation-extensions
cfnex -i {inFile} -o {outFile}
Description
This is designed to make using Amazon's CloudFormation template format easier, more understandable, and more maintainable. CloudFormation templates are incredibly powerful, but quickly become complicated, and you end up with multiple thousands of lines of JSON which isn't very practical. Writing CloudFormation templates using cfnex retains the power of vanilla CloudFormation templates whilst increasing readability and maintainability.
Writing a cfnex extension is as easy as creating a function which takes an object and returns a promise. You can find examples of this in the extensions folder and a tutorial below.
Writing Cfnex Templates
You write cfnex templates the same way you would regular CloudFormation templates, but with the ability to call cfnex extensions the same way you would "Intrinsic Functions" ( Fn::GetAtt
, Fn::Join
, etc. ), like so:
{ "cfnex::extensionName" : [ "aString", {"anObject": "argument2"}, 42 ] }
Where the array there are the arguments to be passed to the extension.
Out of the box cfnex comes with two extensions:
include
includeFile
include
allows you to include another JSON or JS file, and includeFile
allows you to include a raw file.
The output of an extension is then parsed as cfnex template, so you can do things recursively.
Built-in Extensions
include
Extension
Example
A raw cloudformation.json
file which looks like this:
{
"AWSTemplateFormatVersion" : "2010-09-09",
"Description" : "projectname Stack",
"Parameters" : {
"s3BucketName" : {
"Type" : "String",
"Description" : "S3 Bucket Name",
"Default" : "project.name"
},
"redisSize": {
"Type" : "String",
"Description" : "Redis Size",
"Default" : "cache.t2.micro"
},
"rdbmsSize": {
"Type" : "String",
"Description" : "RDBMS Size",
"Default" : "db.t2.micro"
}
}
}
Becomes two files:
a root cloudformation.cfnex.json
file
{
"AWSTemplateFormatVersion" : "2010-09-09",
"Description" : "projectname Stack",
"Parameters" : { "cfnex::include" : [ "./parameters.json" ] },
}
and a separate parameters.json
file
{
"s3BucketName" : {
"Type" : "String",
"Description" : "S3 Bucket Name",
"Default" : "project.name"
},
"redisSize": {
"Type" : "String",
"Description" : "Redis Size",
"Default" : "cache.t2.micro"
},
"rdbmsSize": {
"Type" : "String",
"Description" : "RDBMS Size",
"Default" : "db.t2.micro"
}
}
include-file
extension
A raw cloudformation.json
file which includes this:
"UserData" : { "Fn::Base64" : { "Fn::Join" : ["", [
"#!/bin/bash\n",
"echo ECS_CLUSTER=", { "Ref": "EcsCluster" }, " >> /etc/ecs/ecs.config"
] ] } }
a root cloudformation.cfnex.json
file
"UserData" : { "Fn::Base64" : { "cfnex::include-file" : [ "./ec2/boot.sh" ] } }
and a separate ./ec2/boot.sh
file
#!/bin/bash
echo ECS_CLUSTER=<%cfnex { "Ref": "EcsCluster" } cfnex%> >> /etc/ecs/ecs.config
Note the usage of <%cfnex
tags in the included file, these can be used to include JSON in the included file.
Configuration
Your can override where cfnex looks for your extensions by having a .cfnexrc
JSON file in the directory you run cfnex
in which looks like this:
{
"extensionsDirectory": "customDirName",
}
Writing your own extensions
You can write your own extensions by having an extensions
directory, and within it your custom extensions, where the name of the extension is the filename, so if I wanted to refer to my extension as
{ "cfnex::includeYaml" : [ "myfile.yml" ] }
My extensions
directory would look like this:
extensions
- includeYaml.js
A cfnex extension is a function which returns a Promise
which resolves to be an object.
The function to be ran must be module.export
ed from the file.
The function will be called with two parameters: args
and context
.
args
is whatever the extension was passed in the cfnex template file, so for our includeYaml
extension it'd be
[ "myfile.yml" ]
context
is an object which contains two properties:
cwd
- String - the absolute current working directory that you're being ran inlogger
- Object - a logging helper which hasok
,error
,debug
, andinfo
properties for you to use instead of plainconsole.log
etc.
The object you return must have a property called output
which is the output of your extension which will be
the object can optionally have another property called contextChanges
which should be an object. You can use this to override the context
for any cfnex templates your extension returns.
CLI Usage
Usage:
CloudFormation Extensions (cfnex) [OPTIONS] [ARGS]
Options:
-i, --inFilePath FILE Input cfnex JSON file
-o, --outFilePath DIR Write to FILE rather than the console
--cwd DIR Override the working directory (defaults to the input file's directory)
-k, --no-color Omit color from output
--debug Show debug information
-v, --version Display the current version
-h, --help Display help and usage details