MacroSample

LambdaSharp CloudFormation Macro Definition

Before you begin, make sure to setup your LambdaSharp CLI.

Module Definition

Creating a function that is invoked by a CloudFormation macro is straightforward. First, define the function in the Items section that will be invoked by the macro. Second, create the macro definition using the Macro attribute and specify the function as its handler. Note that a single Lambda function can handle multiple CloudFormation macros.

NOTE: Support for CloudFormation Macros in LambdaSharp is still experimental.

Module: Sample.Macro
Description: A sample module defining CloudFormation macros
Items:

  - Macro: StringToUpper
    Handler: MyFunction

  - Macro: StringToLower
    Handler: MyFunction

  - Function: MyFunction
    Description: This function is invoked by a CloudFormation macros
    Memory: 128
    Timeout: 30

Function Code

The macro invocation can be handled by the ALambdaFunction<T> base class.

public sealed class Function : ALambdaFunction<MacroRequest, MacroResponse> {

    //--- Methods ---
    public override Task InitializeAsync(LambdaConfig config)
        => Task.CompletedTask;

    public override async Task<MacroResponse> ProcessMessageAsync(MacroRequest request) {
        LogInfo($"AwsRegion = {request.region}");
        LogInfo($"AccountID = {request.accountId}");
        LogInfo($"Fragment = {SerializeJson(request.fragment)}");
        LogInfo($"TransformID = {request.transformId}");
        LogInfo($"Params = {SerializeJson(request.@params)}");
        LogInfo($"RequestID = {request.requestId}");
        LogInfo($"TemplateParameterValues = {SerializeJson(request.templateParameterValues)}");

        // macro for string operations
        try {
            if(!request.@params.TryGetValue("Value", out object value)) {
                throw new ArgumentException("missing parameter: 'Value");
            }
            if(!(value is string text)) {
                throw new ArgumentException("parameter 'Value' must be a string");
            }
            string result;
            switch(request.transformId) {
            case "StringToUpper":
                result = text.ToUpper();
                break;
            case "StringToLower":
                result = text.ToLower();
                break;
            default:
                throw new NotSupportedException($"requested operation is not supported: '{request.transformId}'");
            }

            // return successful response
            return new MacroResponse {
                requestId = request.requestId,
                status = "SUCCESS",
                fragment = result
            };
        } catch(Exception e) {

            // an error occurred
            return new MacroResponse {
                requestId = request.requestId,
                status = $"ERROR: {e.Message}"
            };
        }
    }
}