Add a couple of AWS exercises

Questions as well were added.

exercises/aws/solutions/security_groups.md

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+## AWS EC2 - Security Groups
+
+### Requirements 
+
+For this exercise you'll need:
+
+1. EC2 instance with web application
+2. Security group inbound rules that allow HTTP traffic
+
+### Objectives
+
+1. List the security groups you have in your account, in the region you are using
+2. Remove the HTTP inbound traffic rule
+3. Can you still access the application? What do you see/get?
+4. Add back the rule
+5. Can you access the application now?
+
+### Solution
+
+#### Console
+
+1. Go to EC2 service - > Click on "Security Groups" under "Network & Security"
+   You should see at least one security group. One of them is called "default"
+2. Click on the security group with HTTP rules and click on "Edit inbound rules".
+   Remove the HTTP related rules and click on "Save rules"
+3. No. There is a time out because we removed the rule allowing HTTP traffic.
+4. Click on the security group -> edit inbound rules and add the following rule:
+  * Type: HTTP
+  * Port range: 80
+  * Source: Anywhere -> 0.0.0.0/0
+5. yes
+
+#### CLI
+
+1. `aws ec2 describe-security-groups` -> by default, there is one security group called "default", in a new account
+2. Remove the rule:
+
+```
+aws ec2 revoke-security-group-ingress \
+    --group-name someHTTPSecurityGroup
+    --protocol tcp \
+    --port 80 \
+    --cidr 0.0.0.0/0
+```
+3. No. There is a time out because we removed the rule allowing HTTP traffic.
+4. Add the rule we remove:
+
+```
+aws ec2 authorize-security-group-ingress \
+    --group-name someHTTPSecurityGroup
+    --protocol tcp \
+    --port 80 \
+    --cidr 0.0.0.0/0
+```
+5. yes