3.1 Basics of bridge-network
Bridge network is the default network driver in Docker and is used to create an isolated network where containers can interact with each other. This network lets containers communicate using IP addresses and hostnames, providing an easy way to organize interaction between various components of multi-container applications.
Bridge network creates a private internal network at the host level that is isolated from the host's external network. Containers connected to this network can communicate with each other but cannot be directly accessed from outside without configuring port forwarding.
Automatic creation of bridge-network
By default, Docker creates a bridge network during installation, and containers launched without specifying a particular network automatically connect to this network.
Example of creating and using containers in a bridge-network
1. Launching containers in the bridge network:
In this example, we launch two containers: container1 with Nginx and container2 with Busybox. Both containers are connected to the default bridge network.
docker run -d --name container1 nginx
docker run -d --name container2 busybox sleep 1000
2. Checking the containers' IP addresses:
To check the IP addresses of the containers, use the docker inspect command.
These commands will output the IP addresses of the containers, which can be used for communication between them.
docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' container1
docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' container2
3. Communicating between containers using IP addresses:
To test the communication between containers, use the ping command from container2 to ping container1.
If the containers are properly connected to the bridge network, the ping command will succeed.
docker exec container2 ping -c 4 <IP_ADDRESS_OF_CONTAINER1>
Explanation: The bridge network provides a simple solution for local applications where containers need to interact with each other while remaining isolated from the external network. Pinging via IP address is a basic way to test network connection, but for more complex applications, DNS configuration or additional network drivers might be required.
3.2 Using Hostnames
Using hostnames to connect containers
Aside from using IP addresses, Docker also lets you use container names to connect them. This makes configuration easier since container names stay constant, unlike IP addresses, which can change when containers are restarted.
Example of connecting via hostname
1. Start containers specifying the bridge network:
docker run -d --name webserver --network bridge nginx
docker run -d --name appserver --network bridge busybox sleep 1000
2. Check connection via hostname:
Use the ping command from the appserver container to ping webserver:
docker exec appserver ping -c 4 webserver
Creating a custom bridge network
Instead of using the default bridge network, you can create a custom bridge network to have better control over container interactions.
Example of creating a custom network
1. Create a custom network:
docker network create --driver bridge my_bridge_network
2. Start containers in the custom network:
docker run -d --name webserver --network my_bridge_network nginx
docker run -d --name appserver --network my_bridge_network busybox sleep 1000
3. Check connection via hostname:
docker exec appserver ping -c 4 webserver
3.3 Examples of Multiple Hosts
Examples of practical usage
Example 1: Web Server and Database
Create a file docker-compose.yml for a web server and database:
version: '3.8'
services:
web:
image: nginx:latest
networks:
- my_bridge_network
db:
image: postgres:latest
environment:
POSTGRES_USER: user
POSTGRES_PASSWORD: password
networks:
- my_bridge_network
networks:
my_bridge_network:
driver: bridge
Run Docker Compose:
docker compose up -d
Check the connection between containers:
docker compose exec web ping -c 4 db
Example 2: Microservices Architecture
Create a file docker-compose.yml for a microservices application:
version: '3.8'
services:
frontend:
image: nginx:latest
networks:
- my_bridge_network
backend:
image: mybackend:latest
networks:
- my_bridge_network
db:
image: postgres:latest
environment:
POSTGRES_USER: user
POSTGRES_PASSWORD: password
networks:
- my_bridge_network
networks:
my_bridge_network:
driver: bridge
Run Docker Compose:
docker compose up -d
Check the connection between containers:
docker compose exec backend ping -c 4 db
docker compose exec frontend ping -c 4 backend
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