feat(lambda): add a newVersion method. (aws#2099)

This method is useful when deploying a Lambda through a CodePipeline.
It creates a new Version every time the CDK code is executed,
that way making sure an updated Lambda Alias will not point to an old Version.

packages/@aws-cdk/aws-lambda/lib/function.ts

@@ -486,6 +486,25 @@ export class Function extends FunctionBase {
     });
   }
 
+  /**
+   * Add a new version for this Lambda, always with a different name.
+   *
+   * This is similar to the {@link addVersion} method,
+   * but useful when deploying this Lambda through CodePipeline with blue/green deployments.
+   * When using {@link addVersion},
+   * your Alias will not be updated until you change the name passed to {@link addVersion} in your CDK code.
+   * When deploying through a Pipeline,
+   * that might lead to a situation where a change to your Lambda application code will never be activated,
+   * even though it traveled through the entire Pipeline,
+   * because the Alias is still pointing to an old Version.
+   * This method creates a new, unique Version every time the CDK code is executed,
+   * and so prevents that from happening.
+   */
+  public newVersion(): Version {
+    const now = new Date();
+    return this.addVersion(now.toISOString());
+  }
+
   private renderEnvironment() {
     if (!this.environment || Object.keys(this.environment).length === 0) {
       return undefined;

packages/@aws-cdk/aws-lambda/test/test.alias.ts

@@ -1,6 +1,5 @@
+import { beASupersetOfTemplate, expect, haveResource, haveResourceLike } from '@aws-cdk/assert';
 import cloudwatch = require('@aws-cdk/aws-cloudwatch');
-
-import { beASupersetOfTemplate, expect, haveResource } from '@aws-cdk/assert';
 import { Stack } from '@aws-cdk/cdk';
 import { Test } from 'nodeunit';
 import lambda = require('../lib');
@@ -41,6 +40,33 @@ export = {
     test.done();
   },
 
+  'can use newVersion to create a new Version'(test: Test) {
+    const stack = new Stack();
+    const fn = new lambda.Function(stack, 'MyLambda', {
+      code: new lambda.InlineCode('hello()'),
+      handler: 'index.hello',
+      runtime: lambda.Runtime.NodeJS610,
+    });
+
+    const version = fn.newVersion();
+
+    new lambda.Alias(stack, 'Alias', {
+      aliasName: 'prod',
+      version,
+    });
+
+    expect(stack).to(haveResourceLike('AWS::Lambda::Version', {
+      FunctionName: { Ref: "MyLambdaCCE802FB" },
+    }));
+
+    expect(stack).to(haveResourceLike('AWS::Lambda::Alias', {
+      FunctionName: { Ref: "MyLambdaCCE802FB" },
+      Name: "prod"
+    }));
+
+    test.done();
+  },
+
   'can add additional versions to alias'(test: Test) {
     const stack = new Stack();