Connecting Containers with Docker Compose Networks
Use Docker Compose to define multi-container apps and let them communicate over an automatically created bridge network using service names.
Connecting Containers with Docker Compose Networks is a free Docker & Kubernetes for Developers lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Docker & Kubernetes for Developers learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why Compose for Networking
Running many containers and wiring their networks by hand is tedious. Docker Compose describes your whole stack in one YAML file and creates a dedicated network so services can find each other.
The Default Compose Network
When you run docker compose up, Compose creates a single user-defined bridge network for the project. Every service joins it automatically, so no manual docker network create is needed.
Service Names as Hostnames
On a Compose network, each service is reachable by its service name via built-in DNS. A service named db is reachable at the hostname db from any other service.
A Minimal Compose File
Two services on one network: a web app and a database.
version: "3.9"
services:
web:
image: myapp:latest
ports:
- "8080:80"
db:
image: postgres:16
environment:
POSTGRES_PASSWORD: secretConnecting to db by Name
Inside the web container, the connection string points to the service name, not an IP:
DATABASE_URL=postgres://postgres:secret@db:5432/postgresDefining Custom Networks
You can declare named networks to isolate groups of services.
services:
web:
image: myapp
networks: [frontend]
api:
image: myapi
networks: [frontend, backend]
db:
image: postgres
networks: [backend]
networks:
frontend:
backend:Network Isolation in Practice
In the example above, web can reach api but NOT db, because they share no network. This limits the blast radius if a frontend container is compromised.
Exposing vs Publishing Ports
expose makes a port reachable only to other containers on the network. ports publishes it to the host. Internal services like databases should usually only be exposed, never published.
Aliases for Services
You can give a service extra DNS names with aliases, handy when migrating from an old hostname.
services:
db:
image: postgres
networks:
backend:
aliases:
- database
- legacy-db
networks:
backend:Connecting to External Networks
Set a network as external: true to attach services to a network created outside this Compose file, sharing it across projects.
networks:
shared:
external: trueInspecting the Network
List and inspect the network Compose created to confirm which containers are attached.
docker network ls
docker network inspect myproject_defaultQuick Check
Test what you have learned.
Recap
You learned that Docker Compose creates a network per project, lets services talk by service name, and supports custom networks for isolation, expose vs ports, aliases, and external networks.
Frequently asked questions
Is the “Connecting Containers with Docker Compose Networks” lesson free?
Yes — the full text of “Connecting Containers with Docker Compose Networks” is free to read here on the web, and the Docker & Kubernetes for Developers course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Docker & Kubernetes for Developers course, upgrade to CoddyKit PRO.
What will I learn in “Connecting Containers with Docker Compose Networks”?
Use Docker Compose to define multi-container apps and let them communicate over an automatically created bridge network using service names. You practise Docker & Kubernetes for Developers with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Docker & Kubernetes for Developers?
No prior experience is required. Docker & Kubernetes for Developers on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Connecting Containers with Docker Compose Networks” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Docker & Kubernetes for Developers lesson?
Yes. Every Docker & Kubernetes for Developers lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Understanding Docker Network Types
- Configuring Container Networks
- Data Persistence with Volumes
- Connecting Containers with Docker Compose Networks