AWS can be easiest to learn and at the same time can be most tedious to learn. I remember when I was learning about the EC2 service, I always got confused what is the use of these different-different terms that come across one after the other during the launching of a new ec2 instance. Like, "Hmm!, I don't know about the VPC, let's learn it. I don't know about the Security Group. let's see it, Let's see this, Let's see that, blah, blah..." But, from my experience, I've found that rather than learning about every service, we can get our hands dirty and can understand by doing some practical examples. So, in this blog just follow me and I'll explain everything about Security Groups, their role in controlling ongoing and outgoing traffic/requests from the ec2 machine or docker containers, and at last how they can act as a fireball by controlling the traffic for your instance.

What are Security Groups?

Security Groups are fundamental to network security in AWS
They control the inflow & outflow traffic of traffic from EC2 Machines

Security Groups.png

Creating a new Security Group

Now we'll understand security groups in detail with a practical approach.

So, let's create a Security Group by logging into the AWS console and selecting the Security Group feature in the EC2 service.
Now create a new security group by clicking on the Create security group button on the top right
On the next page choose an appropriate Security group name and Description with the default VPC. The VPC id can be different in your console, so don't need to worry.
Now, hit the Create security group button on the bottom right to create the Security Group.

Attaching the security group to an ec2 instance

Now create a new ec2 machine by going to the Launch instances wizard and name the instance and edit its Network settings by clicking the edit button and selecting the testing security group we have created so far as shown below.
Make sure to add your favorite key pair to ssh into your machine and start your ec2 machine by clicking the Launch instance button.

SSH into your EC2 machine

In the last step, we've successfully created a new Security Group and attached it to an ec2 machine. Now, let's try ssh into your ec2 machine using the key-pair and the public IP address of your machine into your git-bash/terminal.
No worries! You'll not able to ssh into your machine because remember we've not added any inbound rules to ssh i.e. we need to open port 22 in our inbound to ssh successfully.
Now let's go to the Security Groups and click the testing security group to edit its inbounds rules.
In the next window, click on the Edit inbound rules button to edit inbound rules.
Now add a new rule by clicking the Add rule button given below and hitting the Save rules button.
Now, retry to ssh using the same command given above. You can now able to understand how the security group works.
We can also change the outbound rules in your security group to restrict how you want your ec2 machine can connect to the world wide web but generally it is not required to change anything for beginners.

Exercise to open port 80 for nginx

Till now, I assume you have understood some basics of Security Groups. To better understand how it works, we will install nginx into our ec2 machine and open port 80 to access it.
Now, I assume that you've successfully ssh into your Linux machine. Now, install the nginx into it. 👉👉: This is a sample when you try to ssh into your Amazon Linux 2 machine.
Now, hit enter and nginx will be installed into your ec2 instance. Now, hit the below command to start the nginx service.
```
sudo service nginx start
```
Let's check whether nginx is serving or not by typing the below command. It will give an output similar to the given below. Since the output is very big, so I'm attaching a part of it.
```
curl localhost
```
So, till now we've successfully installed nginx and configured it successfully. Now, let's check that we got some output by browsing your public IP.
Again, no worries! 😂. You don't get any output on your browser because see the security group that it is using doesn't have any inbound rules to port 80 (the port where nginx serves static files by default)
Now edit your inbound rules again and add the port 80 to it and hit the Save rules to save them.
Let's retry and browse your public IP address in your favorite browser. You will be able to see a similar output depending on the Linux instance you have chosen at the start.
It implies that Nginx is successfully installed into your Linux machine.

Now, congratulations guys! You've to learn each and everything to understand the basics of Security Groups. You can check out the official documentation on Security Groups on AWS for more information.

TheSwarnim