Networking allows containers to communiate with each other, and the host system.

Suppose we have,
2 Docker containers on the host system

backend and frontend and they want to connect each other, and they need to surely interact with the host system.

To manage and establish the connection between the participants, we need docker netwoking

We have two 2 quetions

1. How Docker container will take to host
2. How container will have 1:1 chat

How a container can talk to the host OS?

Whenever you create a container,
Docker creates a virtual eth (docker0).

Without this, Docker cannot talk to the host. This is called Bridge Networking, which is the default in Docker.

Similar to bridge networks, we have different types of networks, which we will see soon.

Till then,

You can check the networks with

docker network ls

We have two types of network bridge network and host network

Bridge Network

• As explained above, the bridge act as an interface between the docker conatiner and host OS.

Host Networking

• Containers will directly use the network of the host. Which is not prefereed

• here, when you create a container, docker will directly bind your container with the ip address(eth0) of the host.

Overlay network

• This is very usefull when you have multiple hosts.

Macvlan

• Macvlan networking in Docker enables containers to have their own unique MAC addresses and appear as separate physical devices on the network.

Containers inside the same bridge network will share the same network subnet. so, there will be a direct connection between both
In our case, container 1 and container 2 can directly talk with each other.

Till now, we have discussed different types of different networks,

but we have an underlying issue.

suppose,
that when we have two Docker containers that are connected using the bridge network, they will have to share the docker0 bridge,
which becomes the common path between both the container and host.

This will make the conatiners not secure,

For example, we have 3 containers: backend, frontend, and payment.

Here, the backend and frontend can be kept in one network,
but the payment must be in another network to maintain anonymity.

How do you achieve logical isolation?

This can be achieved using the bridge networking itself.

Docker allows you to create custom bridge networks.

So, in our scenario, one container can talk to the host with Veth or Docker 0, and the other container will talk using the custom bridge network.

As you can see in the diagram, there is no connection between payment and the frontend and backend; therefore, payment is secure.

DEMO

Inspect Container

docker  inspect  container_name  # Inspect container

List Networks

docker  network  ls

Create new network

docker  network  create  new_name  # new bridge netwok will be created

Attach new network to conatiner

docker  run  -d  --network=new_name  --name  payment_container  payment # attachh new_network to the container

However, you can at any point of time, attach the container to bridge network and enable communication

docker  network  connect  bridge  web

Container with the host network

docker  run  -d  --name  demo-host  --network=host  image

Remove network

docker  network  rm  test

There are many things to learn about docker network, more about hosts,overlay, etc., but for a beginner's experience, this much is sufficient.

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