Creating custom bridge networks in Docker - Visual Walkthrough

Process Flow - Creating custom bridge networks

Start

↓

Run: docker network create --driver bridge my_bridge

↓

Docker creates new bridge network

↓

Network available for containers

↓

Containers connect to custom bridge

↓

End

This flow shows how Docker creates a custom bridge network and how containers can connect to it.

Execution Sample

Docker

docker network create --driver bridge my_bridge

docker network ls

docker run -dit --name container1 --network my_bridge alpine sh

Creates a custom bridge network, lists networks, and runs a container connected to the custom bridge.

Process Table

Step	Command	Action	Result
1	docker network create --driver bridge my_bridge	Create a new bridge network named 'my_bridge'	Network 'my_bridge' created
2	docker network ls	List all Docker networks	Shows 'my_bridge' among default networks
3	docker run -dit --name container1 --network my_bridge alpine sh	Run container 'container1' attached to 'my_bridge'	Container 'container1' runs connected to 'my_bridge'
4	docker network inspect my_bridge	Inspect network details	Shows container1 connected to 'my_bridge'
5	docker network create --driver bridge my_bridge	Try to create network with existing name	Error: network with name 'my_bridge' already exists

💡 Execution stops after network creation and container run; duplicate network creation fails.

Status Tracker

Variable	Start	After Step 1	After Step 3	Final
Networks	default, bridge, host, none	default, bridge, host, none, my_bridge	default, bridge, host, none, my_bridge	default, bridge, host, none, my_bridge
Containers	none	none	container1 (on my_bridge)	container1 (on my_bridge)

Key Moments - 2 Insights

Why does the second 'docker network create' command fail?

Because a network named 'my_bridge' already exists as shown in execution_table step 5, Docker prevents duplicate network names.

How do we know the container is connected to the custom bridge network?

In execution_table step 4, inspecting 'my_bridge' shows 'container1' connected, confirming the container uses the custom network.

Visual Quiz - 3 Questions

Look at the execution table, what is the result of step 2?

A Shows 'my_bridge' among default networks

B Creates a new container

C Deletes the network

D Fails with error

💡 Hint

Check the 'Result' column in execution_table row for step 2

At which step does the container 'container1' start running?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' and 'Result' columns for when the container is created

If you rename the network in step 1 to 'custom_net', what changes in the execution table?

A The container connects to default bridge

B The container name changes

C The network name in step 1 and 2 results changes to 'custom_net'

D No changes at all

💡 Hint

Focus on the network name in the 'Command' and 'Result' columns of steps 1 and 2

Concept Snapshot

Create a custom bridge network with:
  docker network create --driver bridge <name>
List networks:
  docker network ls
Run container on custom network:
  docker run --network <name> ...
Avoid duplicate network names to prevent errors.

Full Transcript

This lesson shows how to create a custom Docker bridge network named 'my_bridge'. First, the command 'docker network create --driver bridge my_bridge' creates the network. Then, 'docker network ls' lists all networks including the new one. Next, a container named 'container1' is run attached to 'my_bridge' using 'docker run -dit --name container1 --network my_bridge alpine sh'. Inspecting the network confirms the container is connected. Trying to create the same network again causes an error because the name is already taken. Variables tracked include the list of networks and containers connected. Key points include understanding why duplicate network creation fails and how to verify container network connection. The quizzes test understanding of the execution steps and effects of changing network names.

Practice

1. What is the main purpose of creating a custom bridge network in Docker?

easy

A. To increase the CPU usage of containers

B. To allow containers to communicate privately and securely

C. To automatically update container images

D. To create a backup of container data

Solution

1. Step 1: Understand Docker networking basics

   Docker uses networks to connect containers. The default bridge network is shared and less secure.

2. Step 2: Purpose of custom bridge networks

   Custom bridge networks isolate containers, allowing private and secure communication between them.

3. Final Answer:

   To allow containers to communicate privately and securely -> Option B

4. Quick Check:

   Custom bridge network = private container communication [OK]

Hint: Custom bridge = private container communication [OK]

Common Mistakes:

• Thinking custom bridge increases CPU usage
• Confusing network creation with image updates
• Assuming it creates data backups

2. Which of the following is the correct command to create a custom bridge network named my_bridge?

easy

A. docker network create --driver bridge my_bridge

B. docker create network bridge my_bridge

C. docker network new --type bridge my_bridge

D. docker bridge create network my_bridge

Solution

1. Step 1: Recall Docker network creation syntax

   The correct syntax is docker network create --driver bridge NETWORK_NAME.

2. Step 2: Match the command with the syntax

   docker network create --driver bridge my_bridge matches the correct syntax exactly for creating a bridge network named my_bridge.

3. Final Answer:

   docker network create --driver bridge my_bridge -> Option A

4. Quick Check:

   Correct syntax = docker network create --driver bridge [OK]

Hint: Use 'docker network create --driver bridge NAME' [OK]

Common Mistakes:

• Using wrong command order
• Missing --driver flag
• Using 'new' or 'create' incorrectly

3. Given the command docker network create --driver bridge isolated_net, what will be the output of docker network ls related to this network?

medium

A. No change; the network list remains the same

B. An error message saying 'driver not found' will appear

C. The default bridge network will be removed

D. A new network named 'isolated_net' with driver 'bridge' will appear in the list

Solution

1. Step 1: Understand the effect of the create command

   The command creates a new bridge network named 'isolated_net'.

2. Step 2: Check the network list after creation

   Running docker network ls shows all networks including the newly created 'isolated_net' with driver 'bridge'.

3. Final Answer:

   A new network named 'isolated_net' with driver 'bridge' will appear in the list -> Option D

4. Quick Check:

   New bridge network appears in list [OK]

Hint: New bridge network shows in 'docker network ls' [OK]

Common Mistakes:

• Expecting an error for valid driver
• Thinking default bridge is removed
• Assuming no change in network list

4. You ran docker network create --driver bridge without specifying a network name. What is the likely result?

medium

A. Docker creates a network named 'bridge' by default

B. Docker creates a network with a random generated name

C. Docker throws an error about missing network name

D. Docker creates the default bridge network again

Solution

1. Step 1: Check required arguments for network creation

   The docker network create command requires a network name after options.

2. Step 2: Result of missing network name

   Omitting the network name causes Docker to throw an error indicating the missing argument.

3. Final Answer:

   Docker throws an error about missing network name -> Option C

4. Quick Check:

   Missing name causes error [OK]

Hint: Always specify network name after options [OK]

Common Mistakes:

• Assuming Docker auto-generates network name
• Thinking 'bridge' is default name created
• Confusing with default bridge network

5. You want two containers to communicate only with each other and not with other containers on the host. Which steps correctly create and use a custom bridge network named private_net?

hard

A. Create network with docker network create --driver bridge private_net and run containers with --network private_net

B. Run containers with --link option without creating a network

C. Use default bridge network and assign static IPs manually

D. Create network with docker network create private_net without specifying driver

Solution

1. Step 1: Create a custom bridge network

   Use docker network create --driver bridge private_net to create an isolated network.

2. Step 2: Run containers attached to this network

   Start containers with --network private_net so they communicate only within this network.

3. Final Answer:

   Create network with 'docker network create --driver bridge private_net' and run containers with '--network private_net' -> Option A

4. Quick Check:

   Custom bridge + --network = isolated container communication [OK]

Hint: Create bridge network then run containers with --network [OK]

Common Mistakes:

• Using --link which is deprecated
• Relying on default bridge for isolation
• Omitting --driver option causing default driver