name: creating-subpackages description: Patterns and standards for creating new AWS service subpackages in the monorepo. Use when adding new service packages like Lambda, DynamoDB, Step Functions, etc.

Creating Subpackages Guide

This guide documents the patterns established when creating the Aurora package, which should be followed for all new service subpackages.

Package Structure

packages/
└── <service-name>/
    ├── package.json
    ├── tsconfig.json
    ├── README.md
    ├── src/
    │   ├── index.ts                    # Package exports
    │   ├── constructs/
    │   │   └── <resource>-<variant>.ts # Factory functions
    │   ├── types/
    │   │   ├── <resource>-base.ts      # Base/shared types
    │   │   └── <resource>-<variant>.ts # Variant-specific types
    │   └── util/
    │       └── <resource>-helpers.ts   # Shared utilities
    ├── test/
    │   └── <resource>-<variant>.test.ts
    └── docs/
        └── <resource>-guide.md

Factory Function Pattern

No ID Parameter

Factory functions should NOT take an id parameter. Use the resource name from props as the construct ID.

// ❌ Old pattern - DO NOT USE
export const createFunction = (scope: Construct, id: string, props: FunctionProps) => {
    return new Function(scope, id, { ... });
};

// ✅ New pattern - USE THIS
export const createFunction = (scope: Construct, props: FunctionProps): FunctionResources => {
    return new Function(scope, props.functionName, { ... });
};

Resource ID Naming

Use the resource name from props for ALL resource IDs to prevent collisions:

export const createFunction = (scope: Construct, props: FunctionProps): FunctionResources => {
    const role = new Role(scope, `${props.functionName}-role`, { ... });
    const logGroup = new LogGroup(scope, `${props.functionName}-logs`, { ... });

    const func = new Function(scope, props.functionName, {
        functionName: props.functionName,
        role,
        logGroup,
        // ... other config
    });

    return { function: func, role, logGroup };
};

Type Definitions

Base Configuration Type

Create a base type for shared configuration across variants:

// types/<resource>-base.ts
export type ResourceBaseConfig = {
    /** Resource name - used as construct ID and for resource naming */
    resourceName: string;

    /** Common config properties */
    environment?: string;
    tags?: Record<string, string>;

    // ... other common properties
};

export type ResourceResources = {
    /** The primary resource created */
    resource: PrimaryResource;

    /** Related resources that may be useful to consumers */
    role?: IRole;
    logGroup?: ILogGroup;
};

Variant-Specific Types

Extend the base for specific variants:

// types/<resource>-<variant>.ts
import {ResourceBaseConfig} from './resource-base';

export type VariantResourceProps = ResourceBaseConfig & {
    /** Variant-specific properties */
    variantOption: string;
};

Avoid Unnecessary Type Wrappers

Don't use Omit<> for properties that don't exist:

// ❌ Don't do this
export const CONFIG: Omit<ResourceProps, 'nonExistentProp'> = { ... };

// ✅ Do this
export const CONFIG: ResourceProps = { ... };

Automatic Resource Creation

Constructs should create necessary supporting resources automatically:

export const createFunction = (scope: Construct, props: FunctionProps): FunctionResources => {
    // Create role automatically if not provided
    const role =
        props.existingRole ||
        new Role(scope, `${props.functionName}-role`, {
            roleName: props.roleName || `${props.functionName}-execution-role`,
            assumedBy: new ServicePrincipal('lambda.amazonaws.com'),
            managedPolicies: [ManagedPolicy.fromAwsManagedPolicyName('service-role/AWSLambdaBasicExecutionRole')],
        });

    // Create log group automatically
    const logGroup = new LogGroup(scope, `${props.functionName}-logs`, {
        logGroupName: `/aws/lambda/${props.functionName}`,
        retention: props.logRetention || RetentionDays.ONE_WEEK,
        removalPolicy: props.removalPolicy || RemovalPolicy.DESTROY,
    });

    const func = new Function(scope, props.functionName, {
        functionName: props.functionName,
        role,
        logGroup,
        // ... other config
    });

    return {function: func, role, logGroup};
};

Default Values and Validation

Provide Sensible Defaults

const commonConfig = {
    timeout: props.timeout || Duration.seconds(30),
    memorySize: props.memorySize || 256,
    retries: props.retries ?? 2, // Use ?? for number defaults

    // Conditional defaults based on other props
    logRetention: props.enableDetailedLogging ? props.logRetention || RetentionDays.ONE_MONTH : RetentionDays.ONE_WEEK,
};

Validate Required Dependencies

if (props.enableFeature && !props.requiredConfig) {
    throw new Error(`requiredConfig must be set when enableFeature is true`);
}

Example Stack Pattern

Config Resolver for Local Overrides

// examples/<service>/config/config-resolver.ts
export interface LocalConfig {
    vpcId?: string;
    subnetIds?: string[];
    // ... other overridable values
}

export class ConfigResolver {
    private static localConfig: LocalConfig | undefined;
    private static localConfigLoaded = false;

    private static loadLocalConfig(): LocalConfig | undefined {
        if (!this.localConfigLoaded) {
            try {
                const {LOCAL_CONFIG} = require('../../environments.local');
                this.localConfig = LOCAL_CONFIG;
            } catch {
                this.localConfig = undefined;
            }
            this.localConfigLoaded = true;
        }
        return this.localConfig;
    }

    private static resolve<T extends LocalConfig>(baseConfig: T): T {
        const localConfig = this.loadLocalConfig();
        if (localConfig) {
            return {...baseConfig, ...localConfig};
        }
        return baseConfig;
    }

    public static getDevConfig(): ResourceProps {
        return this.resolve(DEV_CONFIG);
    }
}

Config Files with Placeholders

// examples/<service>/config/<resource>-dev.ts
export const DEV_CONFIG: ResourceProps = {
    resourceName: 'my-resource-dev',

    // Use placeholder values for sensitive/environment-specific config
    vpcId: 'vpc-xxxxxxxxxxxxxxxxx',
    subnetIds: ['subnet-xxxxxxxxxxxxxxxxx', 'subnet-yyyyyyyyyyyyyyyyy'],

    // Dev-appropriate settings
    enableDetailedLogging: true,
    retentionPolicy: RemovalPolicy.DESTROY,
    deletionProtection: false,
};

Example Stack

// examples/<service>/stacks/<resource>-dev-stack.ts
export class ResourceDevStack extends Stack {
    constructor(scope: Construct, id: string, props?: StackProps) {
        super(scope, id, props);

        const config = ConfigResolver.getDevConfig();

        const {resource, role} = createResource(this, {
            ...config,
        });
    }
}

Package Exports

Structure the index.ts to export everything consumers need:

// src/index.ts

// Construct functions
export {createResourceVariantA} from './constructs/resource-variant-a';
export {createResourceVariantB} from './constructs/resource-variant-b';

// Types - organize by category
export type {
    // Base types
    ResourceBaseConfig,
    ResourceResources,

    // Variant types
    VariantAResourceProps,
    VariantBResourceProps,

    // Helper types
    ParameterGroupConfig,
    MonitoringConfig,
} from './types';

// Utilities - only export what's useful to consumers
export {createParameterGroup, createMonitoringAlarm} from './util/resource-helpers';

Testing Requirements

Test Structure

describe('Resource Variant A', () => {
    let app: App;
    let stack: Stack;

    beforeEach(() => {
        app = new App({
            context: {
                /* mock context */
            },
        });
        stack = new Stack(app, 'TestStack', {
            env: {account: '123456789012', region: 'us-east-1'},
        });
    });

    test('creates resource with basic configuration', () => {
        const {resource} = createResourceVariantA(stack, {
            resourceName: 'test-resource',
            // ... required props
        });

        const template = Template.fromStack(stack);
        template.resourceCountIs('AWS::Service::Resource', 1);
        template.hasResourceProperties('AWS::Service::Resource', {
            Property: 'ExpectedValue',
        });
    });

    test('creates supporting resources automatically', () => {
        createResourceVariantA(stack, {
            resourceName: 'test-resource',
        });

        const template = Template.fromStack(stack);
        template.resourceCountIs('AWS::IAM::Role', 1);
        template.resourceCountIs('AWS::Logs::LogGroup', 1);
    });
});

Documentation Standards

TSDoc Requirements

/**
 * Creates a [Service] [Resource] with [key features].
 *
 * @remarks
 * This construct creates a production-ready resource with:
 * - Feature 1
 * - Feature 2
 * - Feature 3
 *
 * @param scope - The construct scope
 * @param props - Configuration properties
 * @returns Resources including the primary resource and supporting resources
 *
 * @example
 * ```typescript
 * import { createResource } from '@cdk-constructs/<service>';
 * import { Duration } from 'aws-cdk-lib';
 *
 * const { resource, role } = createResource(this, {
 *   resourceName: 'my-resource',
 *   timeout: Duration.seconds(30),
 *   memorySize: 512,
 * });
 * ```
 *
 * @see {@link ResourceProps} for configuration options
 * @see https://docs.aws.amazon.com/service/resource.html
 * @public
 */

Common Patterns

Environment-Based Configuration

const isProd = props.environment === 'prod';

const config = {
    // Expensive features gated to prod
    enableBackups: isProd,
    multiAZ: isProd,

    // Safe defaults for non-prod
    deletionProtection: isProd,
    removalPolicy: isProd ? RemovalPolicy.RETAIN : RemovalPolicy.DESTROY,
};

Conditional Resource Creation

// Create optional resources based on configuration
const kmsKey =
    props.createKmsKey && !props.existingKmsKey
        ? new Key(scope, `${props.resourceName}-kms`, {
              enableKeyRotation: true,
              removalPolicy: RemovalPolicy.RETAIN,
          })
        : props.existingKmsKey;

Helper Functions

// util/resource-helpers.ts
export const createParameterGroup = (scope: Construct, props: ParameterGroupConfig): ParameterGroup => {
    return new ParameterGroup(scope, `${props.name}-params`, {
        description: props.description,
        parameters: props.parameters || {},
    });
};

AWS Service-Specific Patterns

Valid Values Documentation

Document valid values for service-specific properties:

/**
 * Instance type for the resource.
 *
 * @remarks
 * Valid instance classes:
 * - T3: Burstable (MICRO, SMALL, MEDIUM, LARGE, XLARGE, XLARGE2)
 * - M6G: General purpose Graviton2 (LARGE and up)
 * - R6G: Memory optimized Graviton2 (LARGE and up, no MEDIUM)
 */
instanceType: InstanceType;

Service Limits and Defaults

// Validate against service limits
if (props.timeout && props.timeout.toSeconds() > 900) {
    throw new Error('Lambda timeout cannot exceed 900 seconds');
}

// Use service-specific defaults
const monitoringInterval = props.enableEnhancedMonitoring
    ? props.monitoringInterval || Duration.seconds(60) // RDS default
    : undefined;

Integration with Root Project

Add to bin/environment.ts

export type ProjectEnvironment = EnvironmentConfig & {
    // ... existing configs

    myResource?: Partial<MyResourceProps>;
};

export const integrationEnvironments: ProjectEnvironment[] = [
    {
        ...devEnv,
        myResource: {
            resourceName: 'my-resource-dev',
        },
    },
];

Add to bin/app.ts

import {MyResourceStack} from '../examples/<service>/stacks/my-resource-stack';

integrationEnvironments.forEach(env => {
    // ... existing stacks

    if (env.myResource) {
        new MyResourceStack(app, `my-resource-${env.name}`, envProps);
    }
});

Checklist for New Subpackages

• Package structure follows standard layout
• Factory functions use resource name from props (no id parameter)
• Resource IDs use resource name for specificity
• Supporting resources created automatically
• Types properly structured (base + variants)
• No unnecessary Omit<> type wrappers
• Sensible defaults provided
• Service-specific validations implemented
• Config resolver pattern for examples
• Placeholder values in base configs
• Example stacks for dev and prod
• Comprehensive TSDoc documentation
• Test coverage for all variants
• Package exports properly organized
• Package README with usage examples
• Root README.md updated with new package (compatibility matrix, dependency resolution, installation, build commands, publish commands, workspace structure)
• Integration with root project complete