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Breeze - Generate Lambda API

The breeze package subcommand generate-lambda-api provides the code to build a Serverless REST API in Swift based on AWS Lambda, APIGateway and DynamoDB.

Abstract

The following diagram represents the infrastructure architecture of a CRUD REST Serverless API:

AWS Serverless Rest API

The APIGateway exposes the API interface through endpoints and converts the HTTP requests to APIGatewayV2Request events for the Lambdas. Each Lambda receives events from the APIGateway, decodes the events to extract parameters, operates on a DynamoDB table and returns a response payload to the APIGateway. DynamoDB will be accessed through the Lambdas to persist a key-value pair representing data.

With a single line of code, Breeze implements all the Lambdas required for the CRUD interface converting APIGatewayV2Request to an operation on a DynamoDB table and responding with APIGatewayV2Response to the APIGateway.

Usage

Lambda customisation

Define a Codable struct or class like the Item one's in the example and pass it to BreezeLambdaAPI using the type placeholder.

import Foundation
import BreezeLambdaAPI
import BreezeDynamoDBService

struct Item: Codable {
    public var key: String
    public let name: String
    public let description: String
    public var createdAt: String?
    public var updatedAt: String?
    
    enum CodingKeys: String, CodingKey {
        case key
        case name
        case description
        case createdAt
        case updatedAt
    }
}

extension Item: BreezeCodable { }

BreezeLambdaAPI<Item>.main()

It's required the Codable struct or class to conform to the BreezeCodable protocol:

public protocol BreezeCodable: Codable {
    var key: String { get set }
    var createdAt: String? { get set }
    var updatedAt: String? { get set }
}

The code above is the business logic required inside all the Lambdas. All you need to do is to decide the struct conforming BreezeCodable to persist on DynamoDB.

Each lambda will be initialized with a specific _HANDLER and it will run the code to implement the required logic needed by one of the CRUD functions. The code needs to be packaged and deployed using the referenced architecture.

Optimistic locking

Optimistic locking is a strategy to ensure that the BreezeCodable Item is not updated by another request before updating or deleting it. The fields updatedAt and createdAt are used to implement optimistic locking. Refer to the DynamoDB documentation for more details.

Lambda package with Swift Package Manager

To package the Lambda is required to create a Swift Package using the following Package.swift file.

// swift-tools-version:5.7
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "swift-breeze-item-api",
    platforms: [
        .macOS(.v13),
    ],
    products: [
        .executable(name: "ItemAPI", targets: ["ItemAPI"]),
    ],
    dependencies: [
        .package(url: "https://github.com/swift-serverless/Breeze.git", from: "0.2.0"),
    ],
    targets: [
        .executableTarget(
            name: "ItemAPI",
             dependencies: [
                .product(name: "BreezeLambdaAPI", package: "Breeze"),
                .product(name: "BreezeDynamoDBService", package: "Breeze"),
            ]
        )
    ]
)

To be executed on a Lambda, the package needs to be built on AmazonLinux2 and deployed.

Deployment Examples

The API can be deployed on AWS in multiple ways.

Refer to the Examples/ItemAPI folder to explore a deployment example using the Serverless Framework.

Generate the deployment with the command line

The package contains a command line tool to generate the deployment of the swift package, the serverless.yml file and the relevant commands to deploy the Lambda code on AWS using the Serverless Framework.

The command line tool

swift run breeze generate-lambda-api --help

output:

USAGE: breeze generate-lambda-api --config-file <config-file> --target-path <target-path> [--force-overwrite] [-y]

OPTIONS:
  -c, --config-file <config-file>
                          YML configurarion file
  -t, --target-path <target-path>
                          Target path
  -f, --force-overwrite   Force target path overwrite
  -y
  -h, --help              Show help information.

Configuration file

Define a configuration file with the following format:

service: swift-breeze-rest-item-api
 awsRegion: us-east-1
 swiftVersion: 5.10.1
 swiftConfiguration: release
 packageName: BreezeItemAPI
 buildPath: build
 cors: false
 authorizer: #optional
         name: appleJWT
         type: JWTAuthorizer
         issuerUrl: https://appleid.apple.com
         audience:
             - APP_BUNDLE_IDENTIFIER #Change this with the App BUNDLE_IDENTIFIER
 breezeLambdaAPI:
     targetName: ItemAPI
     itemCodable: Item
     itemKey: itemKey
     httpAPIPath: /items
     dynamoDBTableNamePrefix: items

Configuration parameters:

  • awsRegion: AWS Region
  • swiftVersion: Swift version
  • swiftConfiguration: Swift configuration (debug or release)
  • packageName: Swift Package name
  • buildPath: Swift Package build path where the Lambda executable will be generated
  • cors: Enable CORS (default: false)
  • authorizer: Optional. If defined, the API will be protected by the specified authorizer. The authorizer can be a custom one or a predefined one. APP_BUNDLE_IDENTIFIER is the App Bundle Identifier of the iOS App that will use the API. If you don't want to use a custom authorizer, remove the authorizer section.
  • breezeLambdaAPI: Breeze Lambda API configuration
    • targetName: The name of the target that will be generated by the Swift Package Manager
    • itemCodable: The name of the Codable struct or class that will be persisted on DynamoDB
    • itemKey: The name of the key of the Codable struct or class that will be persisted on DynamoDB
    • httpAPIPath: The path of the API
    • dynamoDBTableNamePrefix: The prefix of the DynamoDB table name

Run the command line tool:

The following command will run using the example configuration file and generate the deployment files in the .build/temp folder.

swift run breeze -c Sources/BreezeCommand/Resources/breeze.yml -t .build/temp

output:

⚙️ Loading configuration file

/Users/andreascuderi/Documents/workspace/Breeze/Sources/BreezeCommand/Resources/breeze.yml

service: swift-breeze-rest-item-api
awsRegion: us-east-1
swiftVersion: 5.10.1
swiftConfiguration: release
packageName: BreezeItemAPI
buildPath: build
cors: false
breezeLambdaAPI:
    targetName: ItemAPI
    itemCodable: Item
    itemKey: itemKey
    httpAPIPath: /items
    dynamoDBTableNamePrefix: items

🔎 Verifing target path

🧹 .build/temp

✅ Target path ready!

📁 Generating project from template

📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/SwiftPackage/Package.swift
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/SwiftPackage/Sources/SwiftTarget/main.swift
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/Dockerfile
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/remove.sh
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/.gitignore
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/deploy.sh
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/update.sh
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/Makefile
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/README.md
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/build.sh
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/swagger.json
🛫 .build/temp/SwiftPackage/Sources/SwiftTarget
🛬 .build/temp/SwiftPackage/Sources/ItemAPI
🛫 .build/temp/SwiftPackage
🛬 .build/temp/BreezeItemAPI
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/serverless.yml
📄 /Users/andreascuderi/Documents/workspace/Breeze/.build/temp/serverless-x86_64.yml

✅ Project is ready at target-path

.build/temp

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💨 Use the following commands to build & deploy

cd .build/temp
./build.sh
./deploy.sh

Follow the instructions to build and deploy the project. For more information about the deployment, please refer to the generated README.md file.

Implementation Specs

Lambda initialization

During the Lambda's initialization, the BreezeLambdaAPI reads the configuration from the following Environment variables:

  • AWS_REGION: AWS Region
  • _HANDLER: The handler name specifies the CRUD operation implemented by the Lambda using the following format {executable_name}.{BreezeOperation} or {BreezeOperation}
enum BreezeOperation: String {
    case create
    case read
    case update
    case delete
    case list
}

(example: build/RestAPI.create where build/RestAPI is the executable name and create is the BreezeOperation).

  • DYNAMO_DB_TABLE_NAME: DynamoDB table name.
  • DYNAMO_DB_KEY: DynamoDB Primary Key

APIGateway Requests and Responses

BreezeLambdaAPI receives an APIGateway event, extracts the relevant parameters and performs a BreezeOperation on BreezeDynamoDBService.

  • create

Decodes a BreezeCodable from the APIGatewayV2Request.body and calls createItem on BreezeDynamoDBService. Returns the created BreezeCodable.

  • read

Gets the value of the BreezeCodable.key from the APIGatewayV2Request.pathParameters dictionary and calls readItem on BreezeDynamoDBService. Returns the BreezeCodable if persisted on DynamoDB.

  • update

Decodes a BreezeCodable from the APIGatewayV2Request.body and calls updateItem on BreezeDynamoDBService. Returns the updated BreezeCodable.

  • delete

Gets the value of the BreezeCodable.key from the APIGatewayV2Request.pathParameters dictionary, the value of updatedAt and createdAt from APIGatewayV2Request.queryStringParameters dictionary and calls deleteItem on BreezeDynamoDBService. Returns the BreezeCodable if persisted on DynamoDB.

  • list

Gets the value of the exclusiveStartKey and limit from the APIGatewayV2Request.queryStringParameters dictionary and calls listItems on BreezeDynamoDBService. Returns the ListResponse containing the items if persisted on DynamoDB.

struct ListResponse<T: Codable>: Codable {
    let items: [T]
    let lastEvaluatedKey: String?
}

(See SotoDynamoDB documentation for more info *)