Crate rusty_cdk

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§Rusty CDK

This is not an official AWS project.

Rather, it is an attempt to make Infrastructure as Code safer and easier to use by checking as much as possible at compile time. Think of it as a safe wrapper around unsafe CloudFormation. Also see this blog post.

§Usage

Install using cargo:

cargo add rusty-cdk

Now create a stack, and add infrastructure to it by using builders.

use rusty_cdk::stack::StackBuilder;
use rusty_cdk_core::wrappers::*;

fn main() {
  // prepare a stack builder
  let mut stack_builder = StackBuilder::new();
  // create resource builders, and call `build` to add the resulting resources to the stack
  let stack = stack_builder.build().expect("this stack to build"); // create the stack
  // now `synth` the template or use `deploy` to deploy the stack
}

For example, a queue:

use rusty_cdk::stack::StackBuilder;
use rusty_cdk_core::sqs::QueueBuilder;
use rusty_cdk_core::wrappers::*;
use rusty_cdk_macros::{delay_seconds,message_retention_period};

fn main() {
  let mut stack_builder = StackBuilder::new();
  // create a queue by calling its builder
  // the queue_ref can be used to reference the queue in other resource builders
  let queue_ref = QueueBuilder::new("queue")
          .fifo_queue()
          .content_based_deduplication(true)
          .delay_seconds(delay_seconds!(30))
          .message_retention_period(message_retention_period!(600))
          .build(&mut stack_builder); // add it to the stack builder
  let stack = stack_builder.build().expect("this stack to build");
}

See a list of all available builders below.

Once you’ve done that, you can either synthesize the stack and use any AWS tool (CLI, SDK, console) to deploy it:

let synthesized = stack.synth().unwrap();

Or you can use the built-in deploy function:

rusty_cdk::deploy("MyStackName", stack).await;

§Motivation

This below CDK code is valid at compile time. I.e., it synthesizes (cdk synth) to a CloudFormation template.

// imports

export class CdkStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
      super(scope, id, props);
  
      new Table(this, 'someId', {
          tableName: "examples!!!",
          partitionKey: {
              name: '',
              type: AttributeType.BINARY
          },
          billingMode: BillingMode.PAY_PER_REQUEST,
          maxReadRequestUnits: -1,
          maxWriteRequestUnits: 0,
      })
  }
}

But the code will fail at runtime, because it contains various errors:

table names cannot contain exclamation marks
the partition key name cannot be empty
you cannot set maxReadRequestUnits when billing mode is PAY_PER_REQUEST
a maxReadRequestUnits of -1 does not make sense
maxWriteRequestUnits is similarly not allowed in this situation, and a value of 0 is a bit special. You’re not actually allowed to set this property to zero, but because this is Typescript, the value is interpreted as a falsy and ignored. Meaning the code does not fail, but the resulting stack config is not what you expected.

Fixing these errors can cost a lot of time because you’ll only notice them when you’re deploying the template. That leads to a slow feedback loop, where you’re constantly fixing issues and going through synth and deploy steps, waiting for AWS to tell you where the next issue might be. In other cases, everything will deploy, but it won’t work as expected (see the maxWriteRequestUnits above).

Compare the above with the following:

use rusty_cdk::wrappers::*; // importing all wrappers simplifies larger projects
use rusty_cdk::{non_zero_number, string_with_only_alphanumerics_and_underscores};
use rusty_cdk::dynamodb::{AttributeType, Key, TableBuilder};
use rusty_cdk::stack::{Resource, Stack, StackBuilder};

fn iac() {
  let mut stack_builder = StackBuilder::new();
  
  let dynamo_key = string_with_only_alphanumerics_and_underscores!("test");
  let table_ref = TableBuilder::new("table", Key::new(dynamo_key, AttributeType::String))
            .provisioned_billing()
            .read_capacity(non_zero_number!(5))
            .write_capacity(non_zero_number!(1))
            .build(&mut stack_builder);
  
  let stack = stack_builder.build().unwrap();
  
  // ready to synth and deploy
}

It’s about the same amount of code. But partition keys can now only contain alphanumeric characters and underscores, so we create them through a macro that validates this at compile time. And max read capacity cannot be set when you choose provisioned_billing. Also, adding the resources is less magical (you have to pass in the stack builder), but equally safe (you can’t build a resource without passing it in).

With this kind of tooling, making mistakes becomes much harder, as some mistakes are caught at compile time and others become impossible.

The library does require you to be somewhat more explicit at times. For example, you have to pick a billing mode, as well as read and write capacity for provisioned billing. The CDK ‘helps’ you by setting sensible defaults (5 in this particular case). Which can help you get up and running quickly, but is probably not what you want for any real application. Plus, the compile time guarantees should aid you just as much - if not more - in getting stuff deployed.

§Approach

This project intends to use the tools that Rust offers for ensuring infrastructure correctness at compile time. In some cases, Rust offers help out of the box. E.g., it has multiple number types (both signed and unsigned) that aren’t falsy. In addition, macros and type state are the most important additional tools used here. Const functions would be interesting as well, but they’re too limited for the moment (e.g. I can check a const at compile time, but not a let).

But because compile time checks are sometimes impossible or more challenging, there are also some stack level checks that happen at runtime. Which is why building a stack returns a Result that you unwrap at your own risk.

§Usage of CloudFormation

Just like the AWS CDK, this project uses CloudFormation to actually create the AWS services you request (unlike Terraform which uses API calls).

The main advantage is that it allows me to build on the strong foundations of CloudFormation, but improving safety and ease of use by creating a facade for the infrastructure. And no need to reinvent the wheel of figuring out the dependency graph, etc.

It also has some disadvantages. One is that CloudFormation is slow, in part because it wants to be able to roll back to a stable version if something does go wrong. That’s less important if we’re able to make creating the infrastructure completely safe at compile time. No rollbacks = less time lost.

In time, the project might switch to using SDK calls, to try and make things faster as well as easier.

§Supported services

Currently only a limited number of AWS services are (largely/partly) supported, though the safety varies:

API Gateway
AppConfig
CloudFront
Cloudwatch logs
DynamoDB
IAM
Lambda
S3
SNS
SQS

In other words, you can create serverless applications with this library.

To be added at some point:

Appsync
Athena
Cloudwatch (-logs)
CodeBuild
CodePipeline
DocumentDB
ECS
EventBridge
Kinesis
RDS
Step Functions

§Available builders

Based on rg '^.*?(\w+Builder).*?$' -N -I -r '$1' | sort | uniq | sed -e 's/^/- /'

ApiGatewayV2Builder
ApplicationBuilder
AssumeRolePolicyDocumentBuilder
BucketBuilder
BucketPolicyBuilder
CachePolicyBuilder
ConfigurationProfileBuilder
CorsConfigurationBuilder
CorsRuleBuilder
DefaultCacheBehaviorBuilder
DeploymentStrategyBuilder
DistributionBuilder
EnvironmentBuilder
FunctionBuilder
GenerateSecretStringBuilder
LifecycleConfigurationBuilder
LifecycleRuleBuilder
LifecycleRuleTransitionBuilder
LogGroupBuilder
NonCurrentVersionTransitionBuilder
OriginAccessControlBuilder
OriginBuilder
ParametersInCacheKeyAndForwardedToOriginBuilder
PermissionBuilder
PolicyBuilder
PolicyDocumentBuilder
PrincipalBuilder
PublicAccessBlockConfigurationBuilder
QueueBuilder
QueuePolicyBuilder
RoleBuilder
RolePropertiesBuilder
SecretBuilder
StackBuilder
StatementBuilder
TableBuilder
TopicBuilder
TopicPolicyBuilder
ValidatorBuilder
ViewerCertificateBuilder

§FAQ

“Where can I find examples of how to use this project?”
- Examples can be found in the examples dir
- The snapshot tests in the rusty-cdk dir also provide some usage examples
“I can’t find field X of resource Y. And I would like to use resource Z, which is currently not supported”
- Check whether it’s a legacy field (like maxTTL in DefaultCacheBehavior). If so, I may not have added it, since there’s a newer, recommended, alternative.
- If it’s not a legacy field, I may not have gotten around to adding it yet. I’ve focussed on the properties that I think are most commonly used/useful. You can always open an issue, or add it yourself.
- The same goes for unsupported resources: open an issue or PR!
_“How do I add tags to resources?”
- Currently, you can only add tags to the stack, not to individual resources. These tags are then applied when using the deploy method. They are not present in the CloudFormation template, because unfortunately, templates do not have a root property for tags. See an example below.
- In theory, CloudFormation should propagate the tags to its resources, in practice it will do so in 80–90% of cases.
“I create a resource and my deployment failed”
- If you think that failure could have been avoided at compile time (or before synthesizing), please open an issue
“Wouldn’t it be better if synth / another method was async?”
- Maybe? But keeping everything except for deploy synchronous is easiest for now.
“Won’t this library always be behind on the latest additions/changes to AWS?”
- Sadly, yes. But for a long time that was the case with CloudFormation as well. And sometimes you have to wait for months or a few years before L2-3 constructs arrive in the AWS CDK.
Why don’t you use more borrowing in the internals of this library?
- It started out with less borrowing because that’s easier, less complex. And when I experimented with introducing borrowing everywhere, the performance gain was barely noticeable.

use rusty_cdk::stack::StackBuilder;
use rusty_cdk::sqs::QueueBuilder;

async fn tagging() {
  let mut stack_builder = StackBuilder::new();
  // add your resources
  stack_builder.add_tag("OWNER", "me").build();
  // and deploy
}

§TODO

Pick a style for ids (camelcase?)
Allow overriding of Lambda log group
Multiple queue/topic policy = only last one is applied
- Merge the policies during build? Too bad that this is not transparent though
  - Prefer the user policy id, not our generated one
- Another option is to pass on a ref (but not sure how to implement yet + forgetting to do that would case issues)
- Remove docs pointing out current limitation
UpdateReplacePolicy/DeletionPolicy for storage structs (will slow down testing, so not yet)
More help with IAM permissions
- Additional checks for structure of iam policies
  - For example resources is not required in all cases, but in most contexts it is
Try to replace syn with more something more compile-time lightweight - facet?
Switch to uploading template to s3? helps avoid the 51 kb limit
- Or at least offer that option

Modules§

apigateway
appconfig
cloudfront
cloudwatch
dynamodb
iam
lambda
s3
secretsmanager
shared
sns
sqs
stack
wrappers: Type-safe wrapper types

Macros§

app_config_name: Creates a validated AppConfigName wrapper for AWS AppConfig resource names at compile time.
bucket: Creates a validated Bucket wrapper for existing AWS S3 bucket references at compile time.
bucket_name: Creates a validated BucketName wrapper for new AWS S3 bucket names at compile time.
cf_connection_timeout: Creates a validated CfConnectionTimeout wrapper for CloudFront origin connection timeouts at compile time.
connection_attempts: Checks whether the value that will be wrapped in the ConnectionAttempts struct is between 1 and 3
default_root_object: Creates a validated DefaultRootObject wrapper for CloudFront default root objects at compile time.
delay_seconds: Checks whether the value that will be wrapped in the DelaySeconds struct is between 0 and 900
deployment_duration_in_minutes: Checks whether the value that will be wrapped in the DeploymentDurationInMinutes struct is between 0 and 1440
dto_methods
env_var_key: Creates a validated EnvVarKey wrapper for AWS Lambda environment variable keys at compile time.
growth_factor: Checks whether the value that will be wrapped in the GrowthFactor struct is between 0 and 100
iam_action: Creates a validated IamAction wrapper for AWS IAM permissions at compile time.
lambda_permission_action: Creates a validated LambdaPermissionAction wrapper for Lambda resource-based policy actions at compile time.
lifecycle_object_sizes: Creates a validated S3LifecycleObjectSizes wrapper for S3 lifecycle rule object size constraints at compile time.
lifecycle_transition_in_days: Creates a validated LifecycleTransitionInDays wrapper for S3 lifecycle transition rules at compile time.
location_uri: Creates a validated LocationUri wrapper for AppConfig
log_group_name: Creates a validated LogGroupName wrapper for AWS CloudWatch Logs log group names at compile time.
log_retention: Creates a validated RetentionInDays wrapper for AWS CloudWatch Logs retention periods at compile time.
maximum_message_size: Checks whether the value that will be wrapped in the MaximumMessageSize struct is between 1024 and 1048576
memory: Checks whether the value that will be wrapped in the Memory struct is between 128 and 10240
message_retention_period: Checks whether the value that will be wrapped in the MessageRetentionPeriod struct is between 60 and 1209600
non_zero_number: Creates a validated NonZeroNumber wrapper for positive integers at compile time.
origin_path: Creates a validated OriginPath wrapper for CloudFront origin path prefixes at compile time.
receive_message_wait_time: Checks whether the value that will be wrapped in the ReceiveMessageWaitTime struct is between 0 and 20
ref_struct
s3_origin_read_timeout: Checks whether the value that will be wrapped in the S3OriginReadTimeout struct is between 1 and 120
sqs_event_source_max_concurrency: Checks whether the value that will be wrapped in the SqsEventSourceMaxConcurrency struct is between 2 and 1000
string_for_secret: Creates a validated StringForSecret wrapper for AWS Secrets Manager secret names at compile time.
string_with_only_alphanumerics_and_hyphens: Creates a validated StringWithOnlyAlphaNumericsUnderscoresAndHyphens wrapper at compile time.
string_with_only_alphanumerics_and_underscores: Creates a validated StringWithOnlyAlphaNumericsAndUnderscores wrapper at compile time.
string_with_only_alphanumerics_underscores_and_hyphens: Creates a validated StringWithOnlyAlphaNumericsUnderscoresAndHyphens wrapper at compile time.
timeout: Checks whether the value that will be wrapped in the Timeout struct is between 1 and 900
toml_file: Creates a validated TomlFile wrapper.
type_state
visibility_timeout: Checks whether the value that will be wrapped in the VisibilityTimeout struct is between 0 and 43200
zip_file: Creates a validated ZipFile wrapper for AWS Lambda deployment packages at compile time.

Enums§

DeployError

Functions§

deploy: Deploys a stack to AWS using CloudFormation.
deploy_with_result: Deploys a stack to AWS using CloudFormation.

Crate rusty_cdk

Crate rusty_cdk Copy item path

§Rusty CDK

§Usage

§Motivation

§Approach

§Usage of CloudFormation

§Supported services

§Available builders

§FAQ

§TODO

Modules§

Macros§

Enums§

Functions§

Crate rusty_cdk