feat(lambda): reserved concurrent executions (#1560)

feat(lambda): reserved concurrent executions

Author: Sam Goodwin

packages/@aws-cdk/aws-lambda/README.md

@@ -138,3 +138,18 @@ const fn = new lambda.Function(this, 'MyFunction', {
 ```
 See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/lambda-x-ray.html)
 to learn more about AWS Lambda's X-Ray support.
+
+### Lambda with Reserved Concurrent Executions
+
+```ts
+import lambda = require('@aws-cdk/aws-lambda');
+
+const fn = new lambda.Function(this, 'MyFunction', {
+    runtime: lambda.Runtime.NodeJS810,
+    handler: 'index.handler',
+    code: lambda.Code.inline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'),
+    reservedConcurrentExecutions: 100
+});
+```
+See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/concurrent-executions.html)
+managing concurrency.

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

@@ -172,6 +172,14 @@ export interface FunctionProps {
    * @default undefined X-Ray tracing disabled
    */
   tracing?: Tracing;
+
+  /**
+   * The maximum of concurrent executions you want to reserve for the function.
+   *
+   * @default no specific limit - account limit
+   * @see https://docs.aws.amazon.com/lambda/latest/dg/concurrent-executions.html
+   */
+  reservedConcurrentExecutions?: number;
 }
 
 /**
@@ -339,7 +347,8 @@ export class Function extends FunctionBase {
       memorySize: props.memorySize,
       vpcConfig: this.configureVpc(props),
       deadLetterConfig: this.buildDeadLetterConfig(props),
-      tracingConfig: this.buildTracingConfig(props)
+      tracingConfig: this.buildTracingConfig(props),
+      reservedConcurrentExecutions: props.reservedConcurrentExecutions
     });
 
     resource.addDependency(this.role);

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

@@ -1115,6 +1115,42 @@ export = {
           Runtime: 'ruby2.5' },
           DependsOn: [ 'MyLambdaServiceRole4539ECB6' ] } } });
     test.done();
+  },
+  'support reserved concurrent executions'(test: Test) {
+    const stack = new cdk.Stack();
+
+    new lambda.Function(stack, 'MyLambda', {
+      code: new lambda.InlineCode('foo'),
+      handler: 'index.handler',
+      runtime: lambda.Runtime.NodeJS,
+      reservedConcurrentExecutions: 10
+    });
+
+    expect(stack).toMatch({ Resources:
+      { MyLambdaServiceRole4539ECB6:
+          { Type: 'AWS::IAM::Role',
+          Properties:
+          { AssumeRolePolicyDocument:
+            { Statement:
+            [ { Action: 'sts:AssumeRole',
+              Effect: 'Allow',
+              Principal: { Service: 'lambda.amazonaws.com' } } ],
+              Version: '2012-10-17' },
+          ManagedPolicyArns:
+          // arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
+            // tslint:disable-next-line:max-line-length
+            [{'Fn::Join': ['', ['arn:', {Ref: 'AWS::Partition'}, ':iam::aws:policy/service-role/AWSLambdaBasicExecutionRole']]}],
+          }},
+        MyLambdaCCE802FB:
+          { Type: 'AWS::Lambda::Function',
+          Properties:
+          { Code: { ZipFile: 'foo' },
+          Handler: 'index.handler',
+          ReservedConcurrentExecutions: 10,
+          Role: { 'Fn::GetAtt': [ 'MyLambdaServiceRole4539ECB6', 'Arn' ] },
+          Runtime: 'nodejs' },
+          DependsOn: [ 'MyLambdaServiceRole4539ECB6' ] } } });
+    test.done();
   }
 };