LoopyLuci Docker Networking Troubleshoot
Diagnosing and fixing Docker network issues.
Diagnostics
docker network inspect mynet
docker inspect myapp --format '{{json .NetworkSettings}}' | ConvertFrom-Json
docker exec myapp ping google.com
docker exec myapp nslookup db
docker port myapp
netstat -ano | Select-String ":8080"
DNS Fix
User-defined bridge resolves by name:
services:
app: { networks: [mynet] }
db: { networks: [mynet] }
networks: { mynet: { driver: bridge } }
Port Conflicts
netstat -ano | Select-String ":80"
docker run -p 8080:80 nginx # different host port
Custom DNS
services:
app:
dns: [8.8.8.8, 1.1.1.1]
dns_search: example.com
Pitfalls
- Default bridge has no DNS by name -- use user-defined bridge
- --link is deprecated; use networks
- VPNs break Docker DNS -- set static DNS in daemon.json