Kubernetes - Day - 06 - Network Inside Docker

Different types of Network

Why we need to speak about network ?

1. How a container speak to anothe container ?
2. How a container connect to internet ?

To answer all these questions we need to study different types of Network.

Bridge Network ( default )

• docker0 ( which is the default bridge )
• 172.17.0.0/16 172.17 --> Blocked to Network 0.0/16 --> Available to the Host
• Uses IP tables
• docker 1 runs nginx & docker 2 runs postgres.
• Default bridge --> you can hit docker 1 to the other docker by IP not by its name.
• Container gets random IP's.
• They can't ping each other by name ( no DNS ), only by IP address. Because of this custom network exists.

docker run -d --name web_nginx nginx
docker run -d --name db_test postgres
docker inspect web_nginx

Bridge Network ( Custom )

docker run -d --name web_nginx --network mynetwork nginx
docker run -d --name web_nginx --network mynetwork postgres
docker exec -it web_nginx bash
docker inspect db_test

• Now we can see DNS in the inspect command.
• Inside my give network , i can speak via Domain Name. No need to know the IP. (this is advantage of the custom Bridge Network).
• Every user defined network gets automatic DNS.
• Containers reach each other by NAME, not by IP which is the recommended setup.

Host Network

• The container shares the host IP & port space entirely.
• Fasted option but no isolation.
• Port clashes are possible.

docker run -d --network **host** nginx ( host --> its runs as if like host )

• Instead of creating a separate environment , just run in my host itself.
• It will run as a process or a software.
• There won't be any IP allocated.

None

• You run a container , it can't communicate to the outer world.
• It can used to run Any task.
• No request can be sent inside.
• It will be manily used for Job / cron tab.
• Its an isolated machine.
• Volume mount can be done and necessary packages can be run as container.

docker run -it --network none alphine bash/sh
docker run -it --network none python:3.10.21-alphine3.23

Overlay

• Its like tunnle.

MacVLan

• A conatiner gets a REAL IP & MAC address on the physical network.
• Other networks won't have MAC address , only MacVLan will have the MAC address.
• It will be like " ஒரு laptop பக்கத்துல இன்னொரு laptop இருக்கிற மாதிரி ".

ip addr ( check the IP of the machine ) Eg., 192.168.1.5/24
docker network create -d macvlan --subnet=192.168.1.0/24 --gateway=192.168.1.1 -0 parent=wlp2s0 macvlan
docker run -d --network macvlan_net
docker exec -it <number> bash
docker inspect <number> ( IP will be 192.168.1.2 )

• Eg., It will be used for legcy system to communicate eacf other.

Commands

docker rm -f $(docker ps -aq)
docker run -d --name web_nginx nginx
docker run -d --name db_test postgres
docker inspect web_nginx ( it will show the default bridge network )
docker logs -f db_test
docker network ls ( list the set of networks available )
docker network create mynetwork ( its takes the default Bridge network )
docker run -d --name web_nginx --network mynetwork nginx
docker run -d --name web_nginx --network mynetwork postgres

Notes

• What is Redis ? Redis is a free, open-source, in-memory data structure store used as a database, cache, message broker, and streaming engine.