Networking 101

🛣Networks are like roads and highways to get from Point A to Point B
This works the same way with data going through networks (go from local “roads” to “highways” to communicate with other computers)
If you want to send traffic to a different (non-local) computer/server, you’d have to go through the router as opposed to just communicating with local computers on the same network just using switches.

Conceptual Overview of VPCs

☁️ VPC = virtual private cloud = private subsection of AWS that you control, and use AWS resources/services such as EC2 instances and databases.
May select your own ip address range, subnets, and config of route tables and network gateways.
When you create an AWS account, a default VPC is created for you.
Subnet = sub network, or a sub section of a network. Generally, a subnet includes all of the computers in a specific location.
i.e. all of the houses (computers) on the same street in a neighborhood would be a subnet.
Hierarchy goes: find right network, then the right router, then correct subnet, and finally the correct computer (ip address).
Or high level cloud hierarchy: AWS cloud -> VPC -> Subnet(s) -> AWS Resources (EC2, RDS, etc)
Can have multiple subnets in different AZs with different AWS resources for high availability.

Internet Gateways (IGWs) = hardware + software that provides your private network with a route to the outside world (meaning the internet) of the VPC
Your default VPC already has an IGW attached
IGWs are highly available VPC components so it doesn’t impose any availability risks or bandwidth constraints.
Route Table = talks to IGW to allow lets say an EC2 instance to connect to the internet (outside of your VPC)
RTs are like the GPS of the VPC. They contain a set of rules called Routes that are used to determine where network traffic is directed.
Your default VPC already has a main route table.
Basically a RT helps direct traffic to the right destination.
Networking Security = determining which devices can communicate with each other.

🔐Network Access Control List (NCAL) = A firewall / security layer on the subnet level. Basically like a bouncer saying who can come in or out.
NACL lists have inbound and outbound lists.
I.e. want http traffic to come into your subnet in your VPC, need to add to the NACL
Security Group = A firewall / security layer on the EC2 instance/server level for example. SGs are used when you need multiple EC2 instances on the same subnet but with different security restrictions for some for example.
SGs are like a conference where someone checks if you are allowed into the conference (subnet) and then once in the conference, someone checks which talks/rooms (instances) you can attend in terms of access.
Public subnets = ability to access resources on the internet (because connected through IGW)
Private subnets = no IGW, therefore no access to the resources on the internet
NACL also needs to set both inbound and outbound rules.
Rules are evaluated based on rule # (ordered list), can think of this as priorities of rules.