Miniature Authoritative DNS Server for Network Applications

A system of three servers that illustrate simplified DNS service.
Built with Python, Flask, and Docker

What does it do?

1. User Server (US):

running on port 8080
accepts GET HTTP requests at path
/fibonacci?hostname={FS_HOSTNAME}&fs_port={FS_PORT}&number={N}&as_ip={AS_IP}&as_port={AS_PORT}
if any parameters are missing, US returns HTTP code 400, indicating bad request.
if request succeed, US returns HTTP code 200 with fibonacci number of sequence number N.
US need to query AS to learn IP address of FS_HOSTNAME.

2. Fibonacci Server (FS):

running on port 9090
provides Fibonacci number for a given sequence number N.
2.1 Registration to AS
- accepts a PUT HTTP request at path /register where request body contains following JSON object.
```
{
"hostbane": "{FS_HOSTNAME}"
"ip": "{FS_IP}"
"as_ip": "{AS_IP}"
"as_port": "{AS_PORT}"
}
```
- then register it with AS via UDP on port 53533, using following DNS registration request:
```
TYPE=A
NAME=FS_NAME
VALUE=FS_IP
TTL=10
```
- if the registration succeed, returns a HTTP response with HTTP code 201
2.2 Calculate Fibonacci Number
- accepts GET HTTP request at path /fibonacci?number={N}, and returns Fibonacci number for sequence number N
- if it succeed, returns HTTP code 200.
- if N is not an integer, returns 400 indicating bad format.

3. Authoritative Server (AS)

accept UDP connection on port 53533 and register Type A DNS record into database.
respond to DNS query on port 53533. Check the following sample request and response:
request:
```
TYPE=A
NAME=FS_NAME
```
response:
```
TYPE=A
NAME=FS_NAME
VALUE=FS_IP
TTL=10
```

Preparation:
1. FS registers its hostname with AS
2. AS creates a DNS record for FS and response a result indicating success or failure.
Main function:
1. User (browser) visit: http://{SERVER_IP}:{PORT}/fibonacci?hostname={FS_HOSTNAME}&number={N}&as_ip={AS_IP}
2. US parses FS_HOSTNAME from query string and then query AS for corresponding IP address
3. AS returns corresponding IP address of FS_HOSTNAME to US
4. US requests http://{FS_IP}/fibonacci?number={N}
5. FS returns answer for the fibonacci number with 200 code
6. US returns the result to user (browser).

These instructions will get you a copy of the project up and running on your local machine.

clone the project to your local machine
built the image of each server:
docker build -t {user}/{server_name}:latest .
create a Docker network:
docker network create {netwrk_name}
run each container:
docker run --network {netwrk_name} --name {container_name} -p {port}:{port}/udp -it {user}/{server_name}:latest