The container that cannot claim the host port

Resolve a host port collision without changing the container port.

12 min/Docker / port mapping / compose diagnostics

Observe

Investigate

Fix

Verify

Reflect

docker-compose.yml/yaml

010203040506

services:
  api:
    build: .
    ports:
      - "3000:3000"
    command: npm start

Terminal0 runs

docker: Error response from daemon:
Bind for 0.0.0.0:3000 failed: port is already allocated.

Hint: another local service already owns host port 3000.