Docker Basic Networking

1. The Problem: Dynamic IPs

Containers are ephemeral by nature. When a container restarts, it usually gets a new IP address.

• Hardcoding IPs in application code is fragile and incorrect.
• The moment a container restarts, your application breaks.
• This makes static IP-based communication unreliable.

Solution: Use DNS (Domain Name System) so containers communicate using container names, not IP addresses. Docker provides built-in DNS for supported networks.

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2. Network Drivers

Docker supports multiple network drivers, but in real-world usage you only need to understand these three:

Driver	Description	Use Case
Bridge	Default driver. Creates a private internal network on the host.	Standalone containers
Host	Removes network isolation. Container shares host network directly.	High performance, special network needs
None	Disables all networking.	Secure, fully isolated batch jobs

Practical rule:
90% of your work will use bridge networks. The others are for edge cases.

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3. The Golden Rule: User-Defined Bridges

There are two types of bridge networks in Docker, and they are not equivalent.

1. Default Bridge (bridge)

• Containers attach here automatically.
• No automatic DNS resolution.
• Containers must communicate using IP addresses.
• IPs change on restart.
• Not suitable for production.

2. User-Defined Bridge (Example: my-arch-net)

• Created manually using docker network create.
• Built-in DNS enabled.
• Containers can talk using container names.
• Stable, predictable communication.
• This is the production standard.

Rule you should memorize:
Never use the default bridge for multi-container applications.

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4. Key Commands

Create a Custom Network

docker network create <network_name>

Creates a new user-defined bridge network with built-in DNS.

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List All Networks

docker network ls

Shows all available Docker networks.

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Run a Container on a Specific Network

docker run --network <network_name> ...

Attaches the container directly to the given network instead of the default bridge.

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Inspect a Network

docker network inspect <network_name>

Displays:

• Connected containers
• Container IP addresses
• Network configuration

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By - Chinmay Bagad