feat(elasticloadbalancing): classic load balancer supports ec2 instances

packages/@aws-cdk/aws-elasticloadbalancing/lib/load-balancer.ts

@@ -1,5 +1,5 @@
 import {
-  Connections, IConnectable, ISecurityGroup, IVpc, Peer, Port,
+  Connections, IConnectable, Instance, ISecurityGroup, IVpc, Peer, Port,
   SecurityGroup, SelectedSubnets, SubnetSelection, SubnetType,
 } from '@aws-cdk/aws-ec2';
 import { Duration, Lazy, Resource } from '@aws-cdk/core';
@@ -400,6 +400,24 @@ export class LoadBalancer extends Resource implements IConnectable {
   }
 }
 
+/**
+ * An EC2 instance that is the target for load balancing
+ *
+ * If you register a target of this type, you are responsible for making
+ * sure the load balancer's security group can connect to the instance.
+ */
+export class InstanceTarget implements ILoadBalancerTarget {
+  /**
+   * Create a new Instance target.
+   *
+   * @param instance Instance to register to.
+   * @param connections The network connections associated with this resource.
+   */
+  constructor(public readonly instance: Instance, public readonly connections: Connections) {
+  }
+  public attachToClassicLB(_loadBalancer: LoadBalancer): void {
+  }
+}
 /**
  * Reference to a listener's port just created.
  *

packages/@aws-cdk/aws-elasticloadbalancing/test/loadbalancer.test.ts

@@ -1,8 +1,8 @@
 import { Template } from '@aws-cdk/assertions';
-import { Connections, Peer, SubnetType, Vpc } from '@aws-cdk/aws-ec2';
+import { AmazonLinuxGeneration, Connections, Instance, InstanceClass, InstanceSize, InstanceType, MachineImage, Peer, Port, SecurityGroup, SubnetType, Vpc } from '@aws-cdk/aws-ec2';
 import { testDeprecated } from '@aws-cdk/cdk-build-tools';
 import { Duration, Stack } from '@aws-cdk/core';
-import { ILoadBalancerTarget, LoadBalancer, LoadBalancingProtocol } from '../lib';
+import { ILoadBalancerTarget, InstanceTarget, LoadBalancer, LoadBalancingProtocol } from '../lib';
 
 describe('tests', () => {
   test('test specifying nonstandard port works', () => {
@@ -89,6 +89,78 @@ describe('tests', () => {
     });
   });
 
+  test('add an Instance as load balancing target', () => {
+    // GIVEN
+    const stack = new Stack();
+    const vpc = new Vpc(stack, 'VCP');
+    const securityGroup = new SecurityGroup(stack, 'simple-instance-1-sg',
+      {
+        vpc,
+        allowAllOutbound: true, // will let your instance send outboud traffic
+        securityGroupName: 'simple-instance-1-sg',
+      },
+    );
+
+    // lets use the security group to allow inbound traffic on specific ports
+    securityGroup.addIngressRule(
+      Peer.anyIpv4(),
+      Port.tcp(22),
+      'Allows SSH access from Internet',
+    );
+
+    securityGroup.addIngressRule(
+      Peer.anyIpv4(),
+      Port.tcp(80),
+      'Allows HTTP access from Internet',
+    );
+
+    securityGroup.addIngressRule(
+      Peer.anyIpv4(),
+      Port.tcp(443),
+      'Allows HTTPS access from Internet',
+    );
+    const instance = new Instance(stack, 'targetInstance', {
+      vpc: vpc,
+      instanceType: InstanceType.of( // t2.micro has free tier usage in aws
+        InstanceClass.T2,
+        InstanceSize.MICRO,
+      ),
+      machineImage: MachineImage.latestAmazonLinux({
+        generation: AmazonLinuxGeneration.AMAZON_LINUX_2,
+      }),
+      securityGroup,
+    });
+    const connections = new Connections({
+      peer: Peer.ipv4('666.666.666.666/666'),
+    });
+    const elb = new LoadBalancer(stack, 'LB', {
+      vpc,
+      healthCheck: {
+        interval: Duration.minutes(1),
+        path: '/ping',
+        protocol: LoadBalancingProtocol.HTTPS,
+        port: 443,
+      },
+    });
+
+    // WHEN
+    elb.addListener({ externalPort: 80, internalPort: 8080 });
+    elb.addTarget(new InstanceTarget(instance, connections));
+
+    // THEN: at the very least it added a security group rule for the backend
+    Template.fromStack(stack).hasResourceProperties('AWS::EC2::SecurityGroup', {
+      SecurityGroupEgress: [
+        {
+          Description: 'Port 8080 LB to fleet',
+          CidrIp: '666.666.666.666/666',
+          FromPort: 8080,
+          IpProtocol: 'tcp',
+          ToPort: 8080,
+        },
+      ],
+    });
+  });
+
   test('enable cross zone load balancing', () => {
     // GIVEN
     const stack = new Stack();