fix(experimental-ec2-pattern): Suspend alarm notifications

A scale-in event fires during a rolling update can cause service disruption.
Suspend scaling events during a rolling update for safety.

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

@@ -181,7 +181,9 @@ exports[`The GuEc2AppExperimental pattern matches the snapshot 1`] = `
           "MinInstancesInService": 1,
           "MinSuccessfulInstancesPercent": 100,
           "PauseTime": "PT5M",
-          "SuspendProcesses": [],
+          "SuspendProcesses": [
+            "AlarmNotification",
+          ],
           "WaitOnResourceSignals": true,
         },
       },

src/experimental/patterns/ec2-app.ts

@@ -50,7 +50,14 @@ export class GuEc2AppExperimental extends GuEc2App {
         minInstancesInService: minimumInstances,
         minSuccessPercentage: 100,
         waitOnResourceSignals: true,
-        suspendProcesses: [],
+
+        /*
+        If a scale-in event fires during an `AutoScalingRollingUpdate` operation, the update could fail and rollback.
+        For this reason, we suspend the `AlarmNotification` process, else availability of a service cannot be guaranteed.
+        Consequently, services cannot scale-out during deployments.
+        If AWS ever supports suspending scale-out and scale-in independently, we should allow scale-out.
+         */
+        suspendProcesses: [ScalingProcess.ALARM_NOTIFICATION],
       }),
     });