Rename exercises dir

Name it instead "topics" so it won't be
strange if some topics included "exercises" directory.

topics/aws/exercises/health_checks/exercise.md

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+## AWS Route 53 - Health Checks
+
+## Requirements
+
+3 web instances in different AZs.
+
+## Objectives 
+
+1. For each instance create a health checks with the following properties:
+  1. Name it after the AZ where the instance resides
+  2. Failure threshold should be 5
+
+2. Edit the security group of one of your instances and remove HTTP rules.
+  1. Did it change the status of the health check?

topics/aws/exercises/health_checks/solution.md

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+## AWS Route 53 - Health Checks
+
+## Requirements
+
+3 web instances in different AZs.
+
+## Objectives 
+
+1. For each instance create a health checks with the following properties:
+  1. Name it after the AZ where the instance resides
+  2. Failure threshold should be 5
+
+2. Edit the security group of one of your instances and remove HTTP rules.
+  1. Did it change the status of the health check?
+
+### Solution
+
+#### Console
+
+1. Go to Route 53
+2. Click on "Health Checks" in the left-side menu
+3. Click on "Create health check"
+4. Insert the name: us-east-2
+5. What to monitor: endpoint
+6. Insert the IP address of the instance
+7. Insert the endpoint /health if your web instance supports that endpoint
+8. In advanced configuration, set Failure threshold to 5
+9. Click on "next" and then on "Create health check"
+10. Repeat steps 1-9 for the other two instances you have
+
+1. Go to security group of one of your instances
+2. Click on "Actions" -> Edit inbound rules -> Delete HTTP based rules
+3. Go back to health checks page and after a couple of seconds you should see that the status becomes "unhealthy"