<h2><strong class="bold"><u>Docker Networking</u></strong></h2><h3>Scenario</h3><p>The application will consists of two containers: one for the frontend application, and one for the database. You have security concerns about the database, and you want it to run on a private network that is not publicly accessible.</p><p>In this lab, we will need to create two networks. One will use the frontend application that is publicly accessible, and the other network, which is flagged as internal, is where the database will reside. Create a MySQL container connected to the private network and a Nginx container that is connect to both networks.</p><p></p><h3><u>Create the frontend network</u></h3><p>Use the docker network to create the frontend network:</p><pre class="code-block">docker network create frontend</pre><p></p><h3><u>Create the localhost network</u></h3><p>User the docker network command to create the localhost network:</p><pre class="code-block">docker network create localhost --internal</pre><h3><u>Create a MySQL container</u></h3><p>Create a MySQL container that is attached to the localhost network:</p><pre class="code-block">docker container run -d --name database --network localhost -e MYSQL_ROOT_PASSWORD=P4ssW0rd0! mysql:5.7</pre><h3><u>Create an Nginx container</u></h3><p>Create an Nginx container that is attached to the localhost network:</p><pre class="code-block">docker container run -d --name frontend-app --network frontend nginx:latest</pre><h3><u>Connect frontend-app to the internal network</u></h3><p>Connect frontend-app to the localhost network:</p><pre class="code-block">docker network connect localhost frontend-app</pre><p></p><p></p>

In this lab we will create 2 separate network in docker

How to create Network in Docker 

When the docker is installed on the system, it creates its own Network interface known as "docker0" for communication. 

By default docker has the following network drivers on the host:

It can be checked by running the below command:

The output of the above command is shown below:

The interesting part here is that how the IP address is assigned to the container. Behind the scene what happens is that the default network driver act as a bridge and it allocates the IP addresses to the container by checking the subnet. Let see the example below:

        "Id": "3030fa73577d91dd4143705aa6e136aec31872942bcbfbe0a3a70c4797628416",

        "Created": "2020-05-03T14:08:35.823671481Z",

                    "Subnet": "172.17.0.0/16"

            "com.docker.network.bridge.default_bridge": "true",

            "com.docker.network.bridge.enable_icc": "true",

            "com.docker.network.bridge.enable_ip_masquerade": "true",

            "com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",

            "com.docker.network.bridge.name": "docker0",

            "com.docker.network.driver.mtu": "1500"

The above output shows that the subnet of bridge is "172.17.0.0./16" which concludes that all the containers will have the IP Address within the given range.  

IP Address range can also be customized, which will be explained later in this article.

1.  All the containers running will share the external IP of the host machine using NAT.
2. By-default the new container will always use the bridge network. 
3. Containers run on the separate network , which is internal to docker host. 
4. Bridge network is widely used in Production environment. 

To get the information about the bridge network run the below command:

 Host Network will add the containers on the hosts's network.

 Host network is a good choice when you don't want to isolate the network from host.

Unlike Bridge Network, it will not use the NAT. 

Host Network is not widely used in Production Environment. 

To get the detailed information about the host network run the below command:

We can create the custom network for the containers.

Bridge driver should be used to create the custom network.

Below is the demonstration of how to create the custom network in docker environment. 

 Create a custom bridge network by giving any custom IP Address range of your choice.

$sudo docker network create --subnet=192.168.0.0/24 --gateway=192.168.0.1 mynetwork

where, mynetwork is the name of network defined by user.

2. List the network drivers using below command:

The above screenshot shows the custom network "mynetwork" that was created. It also depicts that the default driver type is "bridge". 

3. Run the container using newly created custom network.

$sudo docker container  run -itd  --network=mynetwork httpd

Where, mynetwork is custom network defined by user and httpd is the name of the image. 

The networks that are being currently used by containers cannot be removed.

Please find the below command to remove the network.

All the unused network can be removed by running the below command. 

In this blog, you will learn some basic concepts about Docket Network.


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