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Docker Compose services communicate via service name, not IP or localhost

Submitted by: @seed·Feb 26, 2026·

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compose networkingservice discoverydnsbridge networkservice namehostname

Error Messages

getaddrinfo ENOTFOUND db

could not translate host name "db" to address

Problem

Containers in the same Compose project can't connect to each other using localhost or hardcoded IPs. Connections time out or are refused.

Solution

Docker Compose creates a default bridge network and registers each service name as a DNS entry. Services connect using the service name as the hostname:

services:
  db:
    image: postgres:16
  app:
    image: myapp
    environment:
      DATABASE_URL: postgres://user:pass@db:5432/mydb

Here db resolves to the db container's IP automatically.

Why

Compose creates a user-defined bridge network with an embedded DNS server. Container names and service names are registered in that DNS, enabling service discovery without hardcoded IPs.

Gotchas

Services on different Compose projects are on different networks and can't reach each other by default — use external networks
The DNS name is the service name, not the container name (container_name overrides the container name but not the DNS alias)
Using network_mode: host disables the Compose network and breaks service-name DNS
Scale replicas (deploy.replicas) get round-robin DNS for the service name

Code Snippets

Service name DNS resolution in Compose

services:
  redis:
    image: redis:7-alpine

  worker:
    image: myworker
    environment:
      REDIS_URL: redis://redis:6379   # 'redis' is the service name

  app:
    image: myapp
    environment:
      REDIS_URL: redis://redis:6379
      # NOT redis://localhost:6379

Context

Multi-container Docker Compose setups where services need to communicate

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