How containers reach each other.
WHAT THE DEFAULT NETWORK PROVIDES
Containers able to reach the outside, and reachable through published ports.
WHAT A USER-DEFINED NETWORK ADDS
Containers reaching each other by name.
WHY THAT MATTERS
Addresses change; names do not.
WHAT THAT REPLACES
Linking containers, an older mechanism now obsolete.
HOW NAME RESOLUTION WORKS
The engine runs a resolver, answering with the container's current address.
WHAT TO USE AS A HOSTNAME
The container or service name.
WHAT PUBLISHING A PORT DOES
Makes it reachable from outside the host.
WHAT NOT PUBLISHING ACHIEVES
The service reachable only by other containers on the same network.
WHY THAT IS THE RIGHT DEFAULT FOR DATABASES
They should not be reachable from outside.
WHAT TO BE CAREFUL WITH
The engine manipulating firewall rules directly.
WHY
A published port may bypass rules you configured.
WHAT TO CHECK
What is actually listening on the host, and on which address.
HOW TO REACH THE HOST FROM INSIDE A CONTAINER
A special hostname the engine provides, which differs by platform.
WHAT TO AVOID
Hard-coding addresses Assuming a container keeps the same address across restarts
WHAT TO PREFER
Names, on a defined network.
