feat(aws-eventbridge-lambda): Support for custom EventBus (#354)

* enhanced construct to support custom EventBus

* fix linting issues

* fix PR review comments

* refactoring and use IEventBus instead of EventBus

* update the props naming convention to align with existing constructs

* updated the props documentation

* upated exisitingEventBusInterface & eventBusProps description

Co-authored-by: santhosh <>

Author: surukonda

Diff for: source/patterns/@aws-solutions-constructs/aws-eventbridge-lambda/README.md

@@ -61,12 +61,15 @@ _Parameters_
 |:-------------|:----------------|-----------------|
 |existingLambdaObj?|[`lambda.Function`](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-lambda.Function.html)|Existing instance of Lambda Function object, providing both this and `lambdaFunctionProps` will cause an error.|
 |lambdaFunctionProps?|[`lambda.FunctionProps`](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-lambda.FunctionProps.html)|User provided props to override the default props for the Lambda function.|
+|existingEventBusInterface?|[`events.IEventBus`](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-events.IEventBus.html)| Optional user-provided custom EventBus for construct to use. Providing both this and `eventBusProps` results an error.|
+|eventBusProps?|[`events.EventBusProps`](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-events.EventBusProps.html)|Optional user-provided properties to override the default properties when creating a custom EventBus. Setting this value to `{}` will create a custom EventBus using all default properties. If neither this nor `existingEventBusInterface` is provided the construct will use the `default` EventBus. Providing both this and `existingEventBusInterface` results an error.|
 |eventRuleProps|[`events.RuleProps`](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-events.RuleProps.html)|User provided eventRuleProps to override the defaults|
 
 ## Pattern Properties
 
 | **Name**     | **Type**        | **Description** |
 |:-------------|:----------------|-----------------|
+|eventBus|[`events.IEventBus`](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-events.IEventBus.html)|Returns the instance of events.IEventBus used by the construct|
 |eventsRule|[`events.Rule`](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-events.Rule.html)|Returns an instance of events.Rule created by the construct|
 |lambdaFunction|[`lambda.Function`](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-lambda.Function.html)|Returns an instance of lambda.Function created by the construct|
 
@@ -82,7 +85,7 @@ Out of the box implementation of the Construct without any override will set the
 * Enable reusing connections with Keep-Alive for NodeJs Lambda function
 * Enable X-Ray Tracing
 * Set Environment Variables
-  * AWS_NODEJS_CONNECTION_REUSE_ENABLED (for Node 10.x and higher functions)
+* AWS_NODEJS_CONNECTION_REUSE_ENABLED (for Node 10.x and higher functions)
 
 ## Architecture
 ![Architecture Diagram](architecture.png)

Diff for: source/patterns/@aws-solutions-constructs/aws-eventbridge-lambda/lib/index.ts

@@ -35,6 +35,18 @@ export interface EventbridgeToLambdaProps {
    * @default - Default props are used
    */
   readonly lambdaFunctionProps?: lambda.FunctionProps,
+  /**
+   * Existing instance of a custom EventBus.
+   *
+   * @default - None
+   */
+  readonly existingEventBusInterface?: events.IEventBus,
+  /**
+   * A new custom EventBus is created with provided props.
+   *
+   * @default - None
+   */
+  readonly eventBusProps?: events.EventBusProps,
   /**
    * User provided eventRuleProps to override the defaults
    *
@@ -45,6 +57,7 @@ export interface EventbridgeToLambdaProps {
 
 export class EventbridgeToLambda extends Construct {
   public readonly lambdaFunction: lambda.Function;
+  public readonly eventBus?: events.IEventBus;
   public readonly eventsRule: events.Rule;
 
   /**
@@ -70,7 +83,13 @@ export class EventbridgeToLambda extends Construct {
       })
     };
 
-    const defaultEventsRuleProps = defaults.DefaultEventsRuleProps([lambdaFunc]);
+    // build an event bus if existingEventBus is provided or eventBusProps are provided
+    this.eventBus = defaults.buildEventBus(this, {
+      existingEventBusInterface: props.existingEventBusInterface,
+      eventBusProps: props.eventBusProps
+    });
+
+    const defaultEventsRuleProps = defaults.DefaultEventsRuleProps([lambdaFunc], this.eventBus);
     const eventsRuleProps = overrideProps(defaultEventsRuleProps, props.eventRuleProps, true);
 
     this.eventsRule = new events.Rule(this, 'EventsRule', eventsRuleProps);