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# Rain

* 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](https://aws.amazon.com/cloudformation/) templates and stacks.

[![Make it Rain](./docs/rain.svg)](https://asciinema.org/a/vtbAXkriC0zg0T2UzP0t63G4S?autoplay=1)

## Discord

Join us on Discord to discuss rain and all things CloudFormation! Connect and interact with CloudFormation developers and
experts, find channels to discuss rain, the CloudFormation registry, StackSets,
cfn-lint, Guard and more:

[![Join our Discord](https://discordapp.com/api/guilds/981586120448020580/widget.png?style=banner3)](https://discord.gg/9zpd7TTRwq)

## Key features

* **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](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference.html) 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 use `rain log --chart` to see a Gantt chart that shows you how long each operation took for a given stack.

* **Build new CloudFormation templates**: `rain build` generates 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 like `AWS::S3::Bucket`, or enable the Bedrock Claude model in your account to use generative AI with a command like `rain build --prompt "A VPC with 2 subnets"`. (Note that Bedrock is not free, and requires some [setup](https://docs.aws.amazon.com/bedrock/latest/userguide/model-access.html)). **NEW** Use the `rain build --recommend` command 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 build` command 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 deploy` creates a new stackset, updates an existing one or adds a stack instance(s) to an existing stack set. You can list stack sets using `rain stackset ls`, review stack set details with `rain stackset ls <stack set name>` and delete stack set and\or its instances with `rain stackset rm <stack set name>`

* **Predict deployment failures** (EXPERIMENTAL): `rain forecast` analyzes 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 pkg` supports client-side module development with the `!Rain::Module` directive. 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 deploy` and `rain rm` support 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._

## Getting started

If you have [homebrew](https://brew.sh/) installed, `brew install rain`

Or you can download the appropriate binary for your system from [the releases page](https://github.com/aws-cloudformation/rain/releases).

Or if you're a [Gopher](https://blog.golang.org/gopher), you can `go install github.com/aws-cloudformation/rain/cmd/rain@latest`

```
{{.Usage}}```

You can find shell completion scripts in [docs/bash_completion.sh](./docs/bash_completion.sh) and [docs/zsh_completion.sh](./docs/zsh_completion.sh).

## Contributing

Rain is written in [Go](https://golang.org/) and uses the [AWS SDK for Go v2](https://github.com/aws/aws-sdk-go-v2).

To contribute a change to Rain, [fork this repository](https://github.com/aws-cloudformation/rain/fork), make your changes, and submit a Pull Request.

### Go Generate

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`.

## License

Rain is licensed under the Apache 2.0 License. 

## Example Usage

### Packaging

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.

#### Embed

The `!Rain::Embed` directive simply inserts the contents of a file into the template as a string.

The template:

```yaml
Resources:
  Test:
    Type: AWS::CloudFormation::WaitConditionHandle
    Metadata:
      Comment: !Rain::Embed embed.txt
```
The contents of `embed.txt`, which is in the same directory as the template:

```txt
This is a test
```

The resulting packaged template:

```yaml
Resources:
  Test:
    Type: AWS::CloudFormation::WaitConditionHandle
    Metadata:
      Comment: This is a test
```

#### Include

The `!Rain::Include` directive parses a YAML or JSON file and inserts the object into the template.

The template:

```yaml
Resources:
  Test:
    !Rain::Include include-file.yaml
```

The file to be included:

```yaml
Type: AWS::S3::Bucket
Properties:
  BucketName: test
```

The resulting packaged template:

```yaml
Resources:
  Test:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: test
```

#### Env

The `!Rain::Env` directive reads environment variables and inserts them into the template as strings.

The template:

```yaml
Resources:
  Test:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: !Rain::Env BUCKET_NAME
```

The resulting packaged template, if you have exported an environment variable named `BUCKET_NAME` with value `abc`:

```yaml
Resources:
  Test:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: abc
```

#### S3Http

The `!Rain::S3Http` directive uploads a file or directory to S3 and inserts the
HTTPS URL into the template as a string.

The template:

```yaml
Resources:
  Test:
    Type: A::B::C
    Properties:
      TheS3URL: !Rain::S3Http s3http.txt
```

If 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.

```yaml
Resources:
  Test:
    Type: A::B::C
    Properties:
      TheS3URL: https://rain-artifacts-012345678912-us-east-1.s3.us-east-1.amazonaws.com/a84b588aa54068ed4b027b6e06e5e0bb283f83cf0d5a6720002d36af2225dfc3
```

#### S3 

The `!Rain::S3` directive is basically the same as `S3Http`, but it inserts the S3 URI instead of an HTTPS URL.

The template:

```yaml
Resources:
  Test:
    Type: A::B::C
    Properties:
      TheS3URI: !Rain::S3 s3.txt
```

If 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.

```yaml
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`.

```yaml
Resources:
  MyFunction:
    Type: AWS::Lambda::Function
    Properties:
      Code: !Rain::S3 
        Path: lambda-dist
        Zip: true
        BucketProperty: S3Bucket
        KeyProperty: S3Key
        Run: buildscript.sh
```

The packaged template:

```yaml
Resources:
  MyFunction:
    Type: AWS::Lambda::Function
    Properties:
      Code:
        S3Bucket: rain-artifacts-012345678912-us-east-1
        S3Key: 1b4844dacc843f09941c11c94f80981d3be8ae7578952c71e875ef7add37b1a7
```

#### Metadata commands

You 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.

```yaml
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 AStackOutputKey
```

`EmptyOnDelete`: 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.

#### Module

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:

```yaml
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: true
```

Note 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):

```yaml
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-value2
```

Note 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`:

```yaml
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: true
```

### Publish modules to CodeArtifact 

Rain 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`.

### Module packaging

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.

```yaml
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.yaml
```

A 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.

#### simple-vpc.yaml

A VPC with just two availability zones. This module is useful for POCs and simple projects.

#### encrypted-bucket.yaml

A simple bucket with encryption enabled and public access blocked

#### compliant-bucket.yaml

A bucket, plus extra buckets for access logs and replication and a bucket policy that should pass most typical compliance checks.

#### bucket-policy.yaml

A bucket policy that denies requests not made with TLS.

#### load-balancer.yaml

An ELBv2 load balancer

#### static-site.yaml

An S3 bucket and a CloudFront distribution to host content for a web site

#### cognito.yaml

A Cognito User Pool and associated resources

#### rest-api.yaml

An API Gateway REST API

#### api-resource.yaml

A Lambda function and associated API Gateway resources

### IfParam and IfNotParam

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.

```yaml
Resources:
  Bucket:
    Type: AWS::S3::Bucket
    Metadata:
      Rain:
        IfParam: Foo
```

If 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.

### Gantt Chart

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`

<img src="./docs/chart.png" />

### Pkl

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](https://github.com/aws-cloudformation/cloudformation-pkl) 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:

```pkl
amends "package://github.com/aws-cloudformation/cloudformation-pkl/releases/download/cloudformation@0.1.1/cloudformation@0.1.1#/template.pkl"
import "package://github.com/aws-cloudformation/cloudformation-pkl/releases/download/cloudformation@0.1.1/cloudformation@0.1.1#/cloudformation.pkl" as cfn
import "package://github.com/aws-cloudformation/cloudformation-pkl/releases/download/cloudformation@0.1.1/cloudformation@0.1.1#/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")
    }
}
```

## Constants

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.

```yaml
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:

```yaml
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
```


## Other CloudFormation tools

* [cfn-lint](https://github.com/aws-cloudformation/cfn-python-lint)

    Validate CloudFormation yaml/json templates against the CloudFormation spec and additional checks. Includes checking valid values for resource properties and best practices.

* [cfn-guard](https://docs.aws.amazon.com/cfn-guard/latest/ug/what-is-guard.html)

    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](https://github.com/aws-cloudformation/aws-guard-rules-registry) to scan your templates for resources that don't comply with common best practices.

* [taskcat](https://github.com/aws-quickstart/taskcat)

    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.