🌐 Docker Networking

Documentation covering Docker networks, ports, and container-to-container communication.

---

🧩 Network Types

• bridge — default network; containers can communicate by service name
• host — no network isolation; container shares host network
• overlay — multi-host networking for Swarm / Kubernetes
• macvlan — container receives its own MAC/IP on the physical network

---

🔧 Common Commands

docker network ls
docker network inspect traefik-net
docker network create mynetwork
docker network rm mynetwork

---

🛠️ Compose Configuration Example

services:
  app:
    networks:
      - traefik-net

networks:
  traefik-net:
    external: true

Notes:

• external: true → the network must exist beforehand
• containers in the same network can communicate via DNS (service name)

---

🔗 Container-to-Container Communication

• Containers in the same network can reach each other using service names Example: http://postgres:5432
• Containers in different networks cannot communicate unless added to a shared network
• ports: is not required for internal communication

---

🚨 Common Issues & Solutions

Problem	Cause	Solution
Container cannot reach another	Different networks	Add both to the same network
Traefik cannot see service	Service not in traefik-net	Add networks: - traefik-net
Port unreachable	Port not exposed or firewall blocking	Check ports: and firewall rules
Port conflict	Another process uses the port	sudo lsof -i :PORT
DNS not working	Corrupted bridge network	Recreate network
Container fails after adding network	Network missing	docker network create traefik-net

---

📘 Example: App + Database + Traefik

services:
  api:
    image: myapp
    networks:
      - backend
      - traefik-net

  db:
    image: postgres
    networks:
      - backend

networks:
  backend:
  traefik-net:
    external: true

Result:

• api ↔ db communicate via backend
• Traefik ↔ api communicate via traefik-net
• db is isolated (no public ports)