Question: I have three table users, cars and enquiries and their design is like:  

**users:**  

id ,name, email  

**cars:**  

id,user\_id,name  

**Enquiry:**  

id, car\_id,description

I just want to know that should I have to keep `user_id` in `Enquiry table` or not.As I know that i can fetch user detail with reference of `car_id` of `cars` table.what is the best way to manage these kind of things.
Thanks in advance.

Answer: 
HTTP is a protocol that sits on top of TCP. Using port 80 is a convention and not a requirement. You can run HTTP (and HTTPS) on any port you want that is available. The way that TCP works, is that a process will open a TCP port (say 8000) and then "listen" on that port for connection attempts from other systems (local or remote). If you try to connect using port 80 on a system listening on port 8000, you will either connect to the wrong service or get connection refused. Only after the connection is accepted does ephemeral ports come into action.

If server A is running a service listening on port 8000, then server B needs to connect to server A using port 8000. This means that server B needs port 8000 open outbound in order to connect to port 8000.

In normal usage, you set (restrict) the inbound ports in a security group and allow ALL outbound ports. Only restrict outbound ports if you understand how TCP works and know exactly what you are doing and why. Otherwise leave all outbound ports open.

There are a few reasons to control outbound ports. For example, to prevent an instance from performing updates, to prevent an instance from communicating if was breached, etc. If you are controlling this level of communications, then you also need to understand how NACLs work and how to use each one.

AWS has some pretty good documentation that explains how security groups and NACLs work and how to use them.
Outbound firewalls are used to limit the connections to external services from within the network. That is why by default all outbound connections are enabled and inbound connections are disabled.

In this case, setting an outbound firewall on server 2 prohibits server 2 from making connections to port 8000 (and all others, except 80) of server 1. It is regardless of the port from which the connection is initiated.