Docker Compose — Default Network

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When you run docker compose up, Compose automatically creates a default network for your project. Every service joins this network and can reach other services by name.

How It Works

┌──────────────────────────────────────┐
│  Project: myapp                      │
│  Network: myapp_default (bridge)     │
│                                      │
│  ┌────────┐  ┌────────┐  ┌───────┐  │
│  │  web   │  │  api   │  │  db   │  │
│  └───┬────┘  └───┬────┘  └───┬───┘  │
│      │           │            │      │
│      └───────────┴────────────┘      │
│              DNS resolution          │
└──────────────────────────────────────┘

The network name is derived from your project directory name plus _default.

Compose File

services:
  web:
    image: nginx:alpine
    ports:
      - "80:80"
  api:
    image: node:20-alpine
    command: node server.js
  db:
    image: postgres:16

No networks: key needed — Compose handles it.

Verify the Network

docker compose up -d
docker network ls

Expected output:

NETWORK ID     NAME              DRIVER    SCOPE
a1b2c3d4e5f6   myapp_default     bridge    local

Service-to-Service Communication

From the web container you can reach api by name:

docker compose exec web ping api

PING api (172.20.0.3): 56 data bytes
64 bytes from 172.20.0.3: seq=0 ttl=64 time=0.123 ms

Inspect the Network

docker network inspect myapp_default

Key output:

{
  "Name": "myapp_default",
  "Driver": "bridge",
  "Containers": {
    "abc123": { "Name": "myapp-web-1", "IPv4Address": "172.20.0.2/16" },
    "def456": { "Name": "myapp-api-1", "IPv4Address": "172.20.0.3/16" },
    "ghi789": { "Name": "myapp-db-1", "IPv4Address": "172.20.0.4/16" }
  }
}

Network Lifecycle

Action Network Behavior
docker compose up Creates network if missing
docker compose down Removes the network
docker compose down -v Removes network + volumes
docker compose stop Keeps the network

Real-World Analogy

Think of the default network as an office LAN — every device on the same floor can find each other by hostname, no special configuration needed.

Summary

Aspect Detail
Created automatically Yes, on docker compose up
Naming convention <project>_default
Driver bridge (default)
Service discovery By service name (DNS)
Removed on docker compose down

Quick Reference

Item Detail
Auto-created Yes, by docker compose up
Name pattern projectname_default
DNS Services reachable by service name
Inspect docker network inspect
Lifecycle Created on up, removed on down

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