feat: added support for layer-provided lambda handlers

refs #548

README.md

@@ -69,6 +69,7 @@ custom:
     includeModules: false # Node modules configuration for packaging
     packager: 'npm' # Packager that will be used to package your external modules
     excludeFiles: src/**/*.test.js # Provide a glob for files to ignore
+    lambdaEntrypoint: null # Provide a custom lambda entrypoint. Useful when using layer provided handlers.
 ```
 
 ### Webpack configuration file

lib/Configuration.js

@@ -16,7 +16,8 @@ const DefaultConfig = {
   packagerOptions: {},
   keepOutputDirectory: false,
   config: null,
-  concurrency: os.cpus().length
+  concurrency: os.cpus().length,
+  lambdaEntrypoint: null
 };
 
 class Configuration {
@@ -82,6 +83,10 @@ class Configuration {
     return this._config.packagerOptions;
   }
 
+  get lambdaEntrypoint() {
+    return this._config.lambdaEntrypoint;
+  }
+
   get config() {
     return this._config.config;
   }

lib/validate.js

@@ -21,6 +21,10 @@ module.exports = {
     const getHandlerFileAndFunctionName = functionDefinition => {
       const { handler: handlerProp, image: imageProp } = functionDefinition;
 
+      // CASE: lambda handler is inside lambda layer. Define custom entrypoint
+      //       alternative solution is to read require('./package.json').main
+      if (this.configuration.lambdaEntrypoint) return this.configuration.lambdaEntrypoint;
+
       if (handlerProp) {
         return handlerProp;
       }