EC2 - IP Addresses

Question 1

What is a Public IP?

Answer 1

It means that a machine can be identified on the internet

Question 2

True or False? Two machines can have the same public IP.

Answer 2

False. It must be unique across the whole web.

Question 3

What is a Private IP?

Answer 3

It means that a machine can only be identified on a private network

Question 4

True or False? Two machines on the same network can have the same private IP address.

Answer 4

The IP must be unique across the private network. However, two different private networks can have the same IP address.

Question 5

True or False? Only a specified range of IPs can be used as a private IP.

Answer 5

True

Question 6

What is an Elastic IP and why would you need it?

Answer 6

It’s a public IPv4 that you own as long as you don’t delete it. It’s used if you need to have a fixed IP for you instance.

Question 7

Why would the public IP for an instance change?

Answer 7

Because the instance had been stopped and started.

Question 8

What is the default amount of Elastic IPs available on your account and how many instances can they be assigned to?

Answer 8

You have 5 available by default. You can only attach it to one instance at a time.

Question 9

Why should you avoid using an Elastic IP, and what are two alternative options?

Answer 9

They often reflect poor architectural decisions.

Alternatives:

1. Use a random public IP and register a DNS name to it
2. Use a Load Balancer and don’t use a public IP

Question 10

Why can’t you SSH to an instance using a private IP?

Answer 10

Because you aren’t on the same network (unless you’re using a VPN).