- Documentation: https://aws-cloudformation.github.io/rain/
Rain is what happens when you have a lot of CloudFormation
Rain is also a command line tool for working with AWS CloudFormation templates and stacks.
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Interactive deployments: With
rain deploy, rain packages your CloudFormation templates, prompts you for any parameters that have not yet been defined, shows you a summary of the changes that will be made, and then displays real-time updates as your stack is being deployed. Once finished, you get a summary of the outcome along with any error messages collected along the way - including errors messages for stacks that have been rolled back and no longer exist. -
Consistent formatting of CloudFormation templates: Using
rain fmt, you can format your CloudFormation templates to a consistent standard or reformat a template from JSON to YAML (or YAML to JSON if you prefer). Rain preserves your comments when using YAML and switches use of intrinsic functions to use the short syntax where possible. -
Combined logs for nested stacks with sensible filtering: When you run
rain log, you will see a combined stream of logs from the stack you specified along with any nested stack associated with it. Rain also filters out uninteresting log messages by default so you just see the errors that require attention. You can also userain log --chartto see a Gantt chart that shows you how long each operation took for a given stack. -
Build new CloudFormation templates:
rain buildgenerates new CloudFormation templates containing skeleton resources that you specify. This saves you having to look up which properties are available and which are required vs. optional. Build skeleton templates by specifying a resource name likeAWS::S3::Bucket, or enable the Bedrock Claude model in your account to use generative AI with a command likerain build --prompt "A VPC with 2 subnets". (Note that Bedrock is not free, and requires some setup). NEW Use therain build --recommendcommand to pick from a list of functional templates that will pass typical compliance checks by default. These templates are great starting points for infrastructure projects. -
Build policy validation files: The
rain buildcommand can now send prompts to the Bedrock Cloude3 Haiku and Sonnet models, which can write Open Policy Agent (OPA) Rego files or CloudFormation Guard files, to verify the compliance of your templates -
Manipulate CloudFormation stack sets:
rain stackset deploycreates a new stackset, updates an existing one or adds a stack instance(s) to an existing stack set. You can list stack sets usingrain stackset ls, review stack set details withrain stackset ls <stack set name>and delete stack set and\or its instances withrain stackset rm <stack set name> -
Predict deployment failures (EXPERIMENTAL):
rain forecastanalyzes a template and the target deployment account to predict things that might go wrong when you attempt to create, update, or delete a stack. This command speeds up development by giving you advanced notice for issues like missing permissions, resources that already exist, and a variety of other common resource-specific deployment blockers. -
Modules (EXPERIMENTAL):
rain pkgsupports client-side module development with the!Rain::Moduledirective. Rain modules are partial templates that are inserted into the parent template, with some extra functionality added to enable extending existing resource types. This feature integrates with CodeArtifact to enable package publish and install. -
Content Deployment (EXPERIMENTAL):
rain deployandrain rmsupport metadata commands that can upload static assets to a bucket and then delete those assets when the bucket is deleted. Rain can also run build scripts before and after stack deployment to prepare content like web sites and lambda functions before uploading to S3.
Note that in order to use experimental commands, you have to add --experimental or -x as an argument.
If you have homebrew installed, brew install rain
Or you can download the appropriate binary for your system from the releases page.
Or if you're a Gopher, you can go install github.com/aws-cloudformation/rain/cmd/rain@latest
Usage:
rain [command]
Stack commands:
cat Get the CloudFormation template from a running stack
cc Interact with templates using Cloud Control API instead of CloudFormation
deploy Deploy a CloudFormation stack or changeset from a local template
logs Show the event log for the named stack
ls List running CloudFormation stacks or changesets
rm Delete a CloudFormation stack or changeset
stackset This command manipulates stack sets.
watch Display an updating view of a CloudFormation stack
Template commands:
bootstrap Creates the artifacts bucket
build Create CloudFormation templates
diff Compare CloudFormation templates
fmt Format CloudFormation templates
forecast Predict deployment failures
merge Merge two or more CloudFormation templates
module Interact with Rain modules in CodeArtifact
pkg Package local artifacts into a template
tree Find dependencies of Resources and Outputs in a local template
Other Commands:
console Login to the AWS console
help Help about any command
info Show your current configuration
You can find shell completion scripts in docs/bash_completion.sh and docs/zsh_completion.sh.
Rain is written in Go and uses the AWS SDK for Go v2.
To contribute a change to Rain, fork this repository, make your changes, and submit a Pull Request.
The README.md, documentation in docs/, the auto completion scripts and a copy of the cloudformation specification in cft/spec/cfn.go are generated through go generate.
Rain is licensed under the Apache 2.0 License.
The rain pkg command can be used as a replacement for the aws cloudformation package CLI command. When packaging a template, rain looks for specific
directives to appear in resources.
The !Rain::Embed directive simply inserts the contents of a file into the template as a string.
The template:
Resources:
Test:
Type: AWS::CloudFormation::WaitConditionHandle
Metadata:
Comment: !Rain::Embed embed.txtThe contents of embed.txt, which is in the same directory as the template:
This is a testThe resulting packaged template:
Resources:
Test:
Type: AWS::CloudFormation::WaitConditionHandle
Metadata:
Comment: This is a testThe !Rain::Include directive parses a YAML or JSON file and inserts the object into the template.
The template:
Resources:
Test:
!Rain::Include include-file.yamlThe file to be included:
Type: AWS::S3::Bucket
Properties:
BucketName: testThe resulting packaged template:
Resources:
Test:
Type: AWS::S3::Bucket
Properties:
BucketName: testThe !Rain::Env directive reads environment variables and inserts them into the template as strings.
The template:
Resources:
Test:
Type: AWS::S3::Bucket
Properties:
BucketName: !Rain::Env BUCKET_NAMEThe resulting packaged template, if you have exported an environment variable named BUCKET_NAME with value abc:
Resources:
Test:
Type: AWS::S3::Bucket
Properties:
BucketName: abcThe !Rain::S3Http directive uploads a file or directory to S3 and inserts the
HTTPS URL into the template as a string.
The template:
Resources:
Test:
Type: A::B::C
Properties:
TheS3URL: !Rain::S3Http s3http.txtIf you have a file called s3http.txt in the same directory as the template,
rain will use your current default profile to upload the file to the artifact
bucket that rain creates as a part of bootstrapping. If the path provided is a
directory and not a file, the directory will be zipped first.
Resources:
Test:
Type: A::B::C
Properties:
TheS3URL: https://rain-artifacts-012345678912-us-east-1.s3.us-east-1.amazonaws.com/a84b588aa54068ed4b027b6e06e5e0bb283f83cf0d5a6720002d36af2225dfc3The !Rain::S3 directive is basically the same as S3Http, but it inserts the S3 URI instead of an HTTPS URL.
The template:
Resources:
Test:
Type: A::B::C
Properties:
TheS3URI: !Rain::S3 s3.txtIf you have a file called s3.txt in the same directory as the template,
rain will use your current default profile to upload the file to the artifact
bucket that rain creates as a part of bootstrapping. If the path provided is a
directory and not a file, the directory will be zipped first.
Resources:
Test:
Type: A::B::C
Properties:
TheS3URI: s3://rain-artifacts-755952356119-us-east-1/a84b588aa54068ed4b027b6e06e5e0bb283f83cf0d5a6720002d36af2225dfc3 If instead of providing a path to a file, you supply an object with properties, you can exercise more control over how the object is uploaded to S3. The following example is a common pattern for uploading Lambda function code. The optional Run property is a local script that you want Rain to run before uploading the content at Path.
Resources:
MyFunction:
Type: AWS::Lambda::Function
Properties:
Code: !Rain::S3
Path: lambda-dist
Zip: true
BucketProperty: S3Bucket
KeyProperty: S3Key
Run: buildscript.shThe packaged template:
Resources:
MyFunction:
Type: AWS::Lambda::Function
Properties:
Code:
S3Bucket: rain-artifacts-012345678912-us-east-1
S3Key: 1b4844dacc843f09941c11c94f80981d3be8ae7578952c71e875ef7add37b1a7You can add a metadata section to an AWS::S3::Bucket resource to take additional actions during deployment, such as running pre and post build scripts, uploading content to the bucket after stack deployment completes, and emptying the contents of the bucket when the stack is deleted.
Resources:
Bucket:
Type: AWS::S3::Bucket
Metadata:
Rain:
EmptyOnDelete: true
Content: site/dist
Version: 2
DistributionLogicalId: SiteDistribution
RunBefore:
Command: buildsite.sh
Args:
- ALiteralArgument
RunAfter:
Command: buildsite.sh
Args:
- Rain::OutputValue AStackOutputKeyEmptyOnDelete: If true, the bucket's contents, including all versions, will be deleted so that the bucket itself can be deleted. This can be useful for development environments, but be careful about using it in production!
Version: Rain doesn't do anything with this, but incrementing the number can force the stack to deploy if there have been no infrastructure changes to the stack.
RunBefore: Rain will run this command before the stack deploys. Useful to run your website build script before bothering to deploy, to make sure it builds successfully.
RunAfter: Rain will run this command after deployment, and it is capable of doing stack output lookups to provide arguments to the script. This is useful if you deployed a resource like an API Gateway and need to know the stage URL to plug in to your website configuration. Use Rain::OutputValue OutputKey to pass one of the arguments to the script.
DistributionLogicalId: Supply the logical id of a CloudFront distribution to invalidate all files in it after the content upload completes.
See test/webapp/README.md for a complete example of using these commands with Rain modules.
The !Rain::Module directive is an experimental feature that allows you to
create local modules of reuseable code that can be inserted into templates.
Rain modules are basically just CloudFormation templates, with a Parameters
section that corresponds to the Properties that a consumer will set when
using the module. Rain modules are very flexible, since you can override
any of the resource properties from the parent template.
In order to use this feature, you have to acknowledge that it's experimental by adding a flag on the command line:
rain pkg -x my-template.yaml
Keep in mind that with new versions of rain, this functionality could change,
so use caution if you decide to use this feature for production applications.
The rain pkg command does not actually deploy any resources if the template
does not upload any objects to S3, so you always have a chance to review the
packaged template. It's recommended to run linters and scanners on the packaged
template, rather than a pre-processed template that makes use of these advanced
directives.
A sample module:
Description: This module creates a compliant bucket, along with a second bucket to store access logs
Parameters:
LogBucketName:
Type: String
Resources:
Bucket:
Type: AWS::S3::Bucket
Properties:
LoggingConfiguration:
DestinationBucketName: !Ref LogBucket
BucketEncryption:
ServerSideEncryptionConfiguration:
- ServerSideEncryptionByDefault:
SSEAlgorithm: AES256
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
Tags:
- Key: test-tag
Value: test-value1
LogBucket:
Type: AWS::S3::Bucket
DeletionPolicy: Retain
Properties:
BucketName: !Ref LogBucketName
BucketEncryption:
ServerSideEncryptionConfiguration:
- ServerSideEncryptionByDefault:
SSEAlgorithm: AES256
VersioningConfiguration:
Status: Enabled
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: trueNote that we defined a single parameter to the module called LogBucketName.
In the module, we create an additional bucket to hold logs, and we apply the
name to that bucket. In the template that uses the module, we specify that name
as a property. This shows how we have extended the basic behavior of a bucket
to add something new.
A template that uses the module (in this example we reference a local module, but it's also possible to reference a URL):
Resources:
ModuleExample:
Type: !Rain::Module "./bucket-module.yaml"
Properties:
LogBucketName: test-module-log-bucket
Overrides:
Bucket:
UpdateReplacePolicy: Delete
Properties:
VersioningConfiguration:
Status: Enabled
Tags:
- Key: test-tag
Value: test-value2Note that in addition to supplying the expected LogBucketName property, we have also
decided to override a few of the properties on the underlying AWS::S3::Bucket resource,
which shows the flexibility of the inheritance model.
The resulting template after running rain pkg:
Resources:
ModuleExampleBucket:
Type: AWS::S3::Bucket
Properties:
LoggingConfiguration:
DestinationBucketName: !Ref ModuleExampleLogBucket
BucketEncryption:
ServerSideEncryptionConfiguration:
- ServerSideEncryptionByDefault:
SSEAlgorithm: AES256
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
Tags:
- Key: test-tag
Value: test-value2
VersioningConfiguration:
Status: Enabled
ModuleExampleLogBucket:
DeletionPolicy: Retain
Type: AWS::S3::Bucket
Properties:
BucketName: test-module-log-bucket
BucketEncryption:
ServerSideEncryptionConfiguration:
- ServerSideEncryptionByDefault:
SSEAlgorithm: AES256
VersioningConfiguration:
Status: Enabled
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: trueRain integrates with AWS CodeArtifact to enable an experience similar to npm
publish and install. A directory that includes Rain module YAML files can be
packaged up with rain module publish, and then the directory can be installed
by developers with rain module install.
You can reference a collection of Rain modules with an alias inside of the
parent template. Add a Rain section to the template to configure the package
alias. There's nothing special about a package, it's just an alias to a
directory or a zip file. A zip file can also have a sha256 hash associated with
it to verify the contents.
Rain:
Packages:
aws:
Location: https://github.com/aws-cloudformation/rain/modules
xyz:
Location: ./my-modules
abc:
Location: https://github.com/aws-cloudformation/rain/releases/tag/m0.1.0/modules.zip
Hash: https://github.com/aws-cloudformation/rain/releases/tag/m0.1.0/modules.sha256
Resources:
Foo:
Type: !Rain::Module aws/foo.yaml
Bar:
Type: !Rain::Module xyz/bar.yaml
Baz:
Type: $abc/baz.yaml
# Shorthand for !Rain::Module abc/baz.yamlA module package is published and released from this repository separately from
the Rain binary release. This allows the package to be referenced by version
numbers using tags, such as m0.1.0 as shown in the example above. The major
version number will be incremented if any breaking changes are introduced to
the modules. The available modules in the release package are listed below.
Treat these modules as samples to be used as a proof-of-concept for building your own module packages.
A VPC with just two availability zones. This module is useful for POCs and simple projects.
A simple bucket with encryption enabled and public access blocked
A bucket, plus extra buckets for access logs and replication and a bucket policy that should pass most typical compliance checks.
A bucket policy that denies requests not made with TLS.
An ELBv2 load balancer
An S3 bucket and a CloudFront distribution to host content for a web site
A Cognito User Pool and associated resources
An API Gateway REST API
A Lambda function and associated API Gateway resources
Inside a module, you can add a Metadata attribute to show or hide resources, depending on whether the parent template sets a parameter value. This is similar to the Conditional section in a template, but somewhat simpler, and it only works in modules.
Resources:
Bucket:
Type: AWS::S3::Bucket
Metadata:
Rain:
IfParam: FooIf the parent template does not set a value for the Foo property, the module will
omit the resource. The opposite is true for IfNotParam.
IfParam can be useful to make flexible modules that can optionally do things like
configure permissions for related resources, like allowing access to a bucket or table.
IfNotParam is useful if you have pre-created a resource and you don't want the module
to create it for you.
Output a chart to an HTML file that you can view with a browser to look at how long stack operations take for each resource.
rain log --chart CDKToolkit > ~/Desktop/chart.html
You can now write CloudFormation templates in Apple's new configuration
language, Pkl. Rain commands that accept input as JSON or YAML now also accept
files with the .pkl extension. We host a Pkl package in a separate
repo that is
generated based on the CloudFormation registry. This package has classes that
can be imported for each registry resource type, in addition to higher level
patterns. This allows you to write a type-safe template and create your own
client-side modules, in a way that is similar to CDK, but with declarative
code.
Example Pkl template:
amends "package://github.com/aws-cloudformation/cloudformation-pkl/releases/download/[email protected]/[email protected]#/template.pkl"
import "package://github.com/aws-cloudformation/cloudformation-pkl/releases/download/[email protected]/[email protected]#/cloudformation.pkl" as cfn
import "package://github.com/aws-cloudformation/cloudformation-pkl/releases/download/[email protected]/[email protected]#/aws/s3/bucket.pkl" as bucket
Description = "Create a bucket"
Parameters {
["Name"] {
Type = "String"
Default = "baz"
}
}
Resources {
["MyBucket"] = new bucket.Bucket {
BucketName = cfn.Ref("Name")
}
}You can put constants into the Rain section in the template and then refer to
those constants later in the template. Constants can be strings or entire
objects (but only strings can be used later in Sub functions). Use the
!Rain::Constant directive to refer to a constant in the template. For
strings, you can add constants to !Sub strings with the
${Rain::ConstantName} pseudo-parameter. Constants can contain previosuly
declared constants in Sub strings using the same format. The Rain section
gets removed during packaging.
Parameters:
Prefix:
Type: String
Rain:
Constants:
Test1: ezbeard-rain-test-constants
Test2: !Sub ${Prefix}-${Rain::Test1}-SubTest
Resources:
Bucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Rain::Constant Test1
Bucket2:
Type: AWS::S3::Bucket
Properties:
BucketName: !Rain::Constant Test2
Bucket3:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub "pre-${Prefix}-${Rain::Test1}-suffix" Run rain pkg on that template to produce the following output:
Parameters:
Prefix:
Type: String
Resources:
Bucket:
Type: AWS::S3::Bucket
Properties:
BucketName: ezbeard-rain-test-constants
Bucket2:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${Prefix}-ezbeard-rain-test-constants-SubTest
Bucket3:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub pre-${Prefix}-ezbeard-rain-test-constants-suffix-
Validate CloudFormation yaml/json templates against the CloudFormation spec and additional checks. Includes checking valid values for resource properties and best practices.
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Guard is a policy evaluation tool that allows you to build your own rules with a custom DSL. You can also pull rules from the guard registry to scan your templates for resources that don't comply with common best practices.
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taskcat is a tool that tests AWS CloudFormation templates. It deploys your AWS CloudFormation template in multiple AWS Regions and generates a report with a pass/fail grade for each region. You can specify the regions and number of Availability Zones you want to include in the test, and pass in parameter values from your AWS CloudFormation template. taskcat is implemented as a Python class that you import, instantiate, and run.
Are we missing an excellent tool? Let us know via a GitHub issue.
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