CUSTOM DOCKER NETWORK

Think of a custom Docker network as a private LAN inside the Docker host (or across hosts, if using Swarm). When you create one, Docker sets up a virtual switch that containers can plug into. This gives us-

• Automatic DNS-based service discovery: Containers can talk to each other using names like web, db, etc.
• Traffic isolation: Containers on different networks can’t talk unless explicitly connected.
• Custom IP ranges: You can define subnets and gateways to avoid conflicts or match your infrastructure.
• Multi-network support: A container can belong to multiple networks, acting as a bridge between services.

REASONS TO REPLACE DEFAULT BRIDGE WITH CUSTOM DOCKER NETWORK-

• Scoped isolation– Custom networks isolate traffic, reducing the risk of unintended cross-container communication.
• Dynamic connect/disconnect– You can attach or detach containers from custom networks at runtime—no restart needed.
• Custom IP/subnet control– Define your own subnets and gateways to avoid conflicts and align with your infrastructure.
• DNS-based service discovery– Containers on a custom network can resolve each other by name—no need for IP juggling.
• Compatibility with orchestration tools– Tools like Docker Compose and Swarm work seamlessly with custom networks for scalable deployments.
• Better debugging and observability– Named networks make it easier to trace traffic and understand container relationships.

TYPES OF DOCKER NETWORK DRIVERS

DRIVER	DESCRIPTION
bridge	Default for single-host container communication
overlay	Enables multi-host networking (requires Docker Swarm)
macvlan	Assigns MAC addresses to containers for direct LAN access
host	Shares the host’s network stack (no isolation)
none	Disables networking entirely for the container

CODE TO CREATE A CUSTOM BRIDGE

docker network create \
–driver bridge \
–subnet 192.168.100.0/24 \
–gateway 192.168.100.1 \
my_custom_net

The above code creates a bridge network with a defined subnet and gateway. Containers attached to this network can talk to each other using container names.

ADVANTAGES OF USING CUSTOM DOCKER NETWORK

1. Traffic isolation– Containers on different custom networks can’t talk to each other unless explicitly connected—great for security and segmentation.
2. Custom IP and subnet control– You can define your own subnets, gateways, and IP ranges to avoid conflicts and align with your infrastructure.
3. Dynamic container management– Attach or detach containers from networks at runtime without restarting them—super handy for CI/CD and scaling.
4. Multi-network support– A container can belong to multiple networks, acting as a bridge between services or layers (e.g., frontend and backend).
5. Better orchestration compatibility– Tools like Docker Compose and Swarm rely on custom networks for clean service grouping and scalable deployments.
6. Service Discovery by name- Containers can communicate using names like db or web instead of IP addresses, thanks to Docker’s built-in DNS.

DISADVANTAGES OF USING CUSTOM DOCKER NETWORK

1. Risk of subnet conflicts– If you define overlapping subnets (e.g., with VPNs or cloud VPCs), it can lead to routing issues and broken connectivity.
2. Debugging challenges– Network-related bugs (like DNS failures or misrouted traffic) can be tricky to diagnose without proper tooling or logging.
3. Performance overhead– Overlay networks (used in Swarm or multi-host setups) introduce latency due to encryption and encapsulation layers.
4. Security misconfigurations– While custom networks offer isolation, misconfigured rules or overly permissive settings can expose services unintentionally.
5. Increased Complexity- Managing multiple networks, subnets, and aliases can make your setup harder to understand and maintain, especially in large environments.
6. Learning curve- For teams new to Docker, understanding how custom networks interact with containers, services, and orchestration tools can be daunting.