chore(elasticloadbalancingv2): Add duration checks for slow start target group attribute (#13265)

One more duration check... safety first :)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: robertd

packages/@aws-cdk/aws-elasticloadbalancingv2/lib/alb/application-target-group.ts

@@ -123,6 +123,9 @@ export class ApplicationTargetGroup extends TargetGroupBase implements IApplicat
 
     if (props) {
       if (props.slowStart !== undefined) {
+        if (props.slowStart.toSeconds() < 30 || props.slowStart.toSeconds() > 900) {
+          throw new Error('Slow start duration value must be between 30 and 900 seconds.');
+        }
         this.setAttribute('slow_start.duration_seconds', props.slowStart.toSeconds().toString());
       }
       if (props.stickinessCookieDuration) {

packages/@aws-cdk/aws-elasticloadbalancingv2/test/alb/target-group.test.ts

@@ -205,4 +205,21 @@ describe('tests', () => {
       });
     }).toThrow(/Stickiness cookie duration value must be between 1 second and 7 days \(604800 seconds\)./);
   });
+
+  test('Bad slow start duration value', () => {
+    // GIVEN
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'Stack');
+    const vpc = new ec2.Vpc(stack, 'VPC', {});
+
+    // THEN
+    [cdk.Duration.minutes(16), cdk.Duration.seconds(29)].forEach((badDuration, i) => {
+      expect(() => {
+        new elbv2.ApplicationTargetGroup(stack, `TargetGroup${i}`, {
+          slowStart: badDuration,
+          vpc,
+        });
+      }).toThrow(/Slow start duration value must be between 30 and 900 seconds./);
+    });
+  });
 });

packages/@aws-cdk/aws-elasticloadbalancingv2/test/integ.alb.expected.json

@@ -469,6 +469,10 @@
         "Port": 80,
         "Protocol": "HTTP",
         "TargetGroupAttributes": [
+          {
+            "Key": "slow_start.duration_seconds",
+            "Value": "60"
+          },
           {
             "Key": "stickiness.enabled",
             "Value": "true"

packages/@aws-cdk/aws-elasticloadbalancingv2/test/integ.alb.ts

@@ -32,6 +32,7 @@ const group2 = listener.addTargets('ConditionalTarget', {
   targets: [new elbv2.IpTarget('10.0.128.5')],
   stickinessCookieDuration: cdk.Duration.minutes(5),
   stickinessCookieName: 'MyDeliciousCookie',
+  slowStart: cdk.Duration.minutes(1),
 });
 
 group1.metricTargetResponseTime().createAlarm(stack, 'ResponseTimeHigh1', {