fix(experimental-ec2-pattern): Set ASG DesiredCapacity

During a deployment, CloudFormation updates the min and desired.

During a rollback (e.g. if the healthcheck failed), CloudFormation only resets the min.
The desired is still elevated, meaning the service is over provisioned.

Explicitly setting the desired property of the ASG ensures CloudFormation rollback puts the ASG back to the initial state,
e.g. correctly provisioned.

src/experimental/patterns/__snapshots__/ec2-app.test.ts.snap

@@ -110,6 +110,7 @@ exports[`The GuEc2AppExperimental pattern matches the snapshot 1`] = `
         },
       },
       "Properties": {
+        "DesiredCapacity": "1",
         "HealthCheckGracePeriod": 120,
         "HealthCheckType": "ELB",
         "LaunchTemplate": {

src/experimental/patterns/ec2-app.test.ts

@@ -44,6 +44,20 @@ describe("The GuEc2AppExperimental pattern", () => {
     expect(Template.fromStack(stack).toJSON()).toMatchSnapshot();
   });
 
+  it("should create an ASG with min, max, and desired capacity set", () => {
+    const stack = simpleGuStackForTesting();
+
+    new GuEc2AppExperimental(stack, { ...initialProps(stack), scaling: { minimumInstances: 5 } });
+
+    Template.fromStack(stack).hasResource("AWS::AutoScaling::AutoScalingGroup", {
+      Properties: {
+        MinSize: "5",
+        MaxSize: "10",
+        DesiredCapacity: "5",
+      },
+    });
+  });
+
   it("should create an ASG with a resource signal count that matches the min instances", () => {
     const stack = simpleGuStackForTesting();
 

src/experimental/patterns/ec2-app.ts

@@ -58,6 +58,8 @@ export class GuEc2AppExperimental extends GuEc2App {
     const { userData, role } = autoScalingGroup;
     const cfnAutoScalingGroup = autoScalingGroup.node.defaultChild as CfnAutoScalingGroup;
 
+    cfnAutoScalingGroup.desiredCapacity = minimumInstances.toString();
+
     cfnAutoScalingGroup.metricsCollection = [
       {
         /*