My home server is multi-homed (multiple outgoing network interfaces) which a lot of the times is more trouble than it's worth... This time around I had a need to route a specific Docker container's traffic through a non-default outgoing interface (i.e. an OpenVPN interface to access secured resources). Below I'll show you how I made that happen. ### Primer on multi-homed networking Controlling incoming connections is generally easier than outgoing. Listening connections can be setup on all interfaces or on a specific IP, which will bind it to a specific incoming interface. Outgoing connections, on the other hand, are a routing decision performed by the kernel. So regardless of the *incoming* connection, data flows *out* (generally) through the default route. [Policy-based routing](https://www.tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.rpdb.simple.html) customizes these routing decisions so that the route -- that is, the outgoing interface -- can be determined by a set of rules like source IP or marked packet by IP…