How to Fix Docker Compose Network Error

In this tutorial, you'll learn about How to Fix Docker Compose Network Error. We cover key concepts, practical examples, and best practices.

You run <a href="/devops/docker-compose/">docker compose</a> up and get network not found or subnet overlaps with another network — Docker Compose cannot find or create the required network.

The Problem

network myapp_default declared as external but could not be found

Or:

Error response from daemon: Pool overlaps with other one on this address space

Step-by-Step Fix

Step 1: List existing Docker networks

docker network ls

Expected:

NETWORK ID     NAME              DRIVER    SCOPE
abc123         bridge            bridge    local
def456         myapp_default     bridge    local

Step 2: Create the missing external network

If your compose file references an external network:

networks:
  my-network:
    external: true

Create it:

docker network create my-network

Step 3: Inspect network configuration

docker network inspect myapp_default

Check for subnet conflicts:

"Subnet": "172.18.0.0/16",
"Gateway": "172.18.0.1"

Step 4: Fix subnet conflicts

If subnets overlap, specify a custom subnet in docker-compose.yml:

networks:
  app-network:
    driver: bridge
    ipam:
      config:
        - subnet: 10.10.0.0/16
          gateway: 10.10.0.1

Then restart:

docker compose down && docker compose up

Step 5: Remove orphaned networks

docker network prune

Step 6: Use project-specific networks

Ensure COMPOSE_PROJECT_NAME is consistent:

export COMPOSE_PROJECT_NAME=myapp
docker compose up

Prevention Tips

• Name your networks explicitly in compose files
• Use unique subnets to avoid overlaps
• Always create external networks before referencing them
• Use <a href="/devops/docker-compose/">docker compose</a> down -v to clean up networks when testing

Common Mistakes with compose network

1. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
2. Using head and tail instead of pattern matching, causing runtime errors on empty lists
3. Forgetting that lazy evaluation defers computation until the value is forced, causing space leaks with unevaluated thunks

These mistakes appear frequently in real-world DOCKER code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

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