Consul: Add -bind-iface to bind consul to a specific interface

[cruatta]

:thought_balloon: Add an option to bind consul to a specific interface and whatever the ip address of that interface is. For example, if I'm provisioning 100 servers, I might know I'll have a bond1 on my servers that I know I want consul to bind to. If it's not the first private interface, I won't be able to rely on 0.0.0.0 and I don't want to have to specify the IP addresses for 100 servers in my configs. Just a thought since a lot of people seem to be having issues with consul binding to interfaces it should not be binding to. Does that make sense?

[ryanuber]

In general the concept makes sense to me, but I wonder what we do in cases where we have multiple IP aliases on a single interface. I'll mark this as a thought ticket for now.

[cruatta]

Ryan, good point. I was thinking about a use case specifically where this is not the case. I think it would be safe to assume if you're using this feature and there is more than one IP on a NIC, consul could issue a warning that it cannot bind reliably to the NIC and fall back on binding as it does to 0.0.0.0

[jness]

This would be a great addition, and would help greatly during our packer base box provisions.

[bof]

May I suggest an alternative configuration to the same end? Instead of specifying an interface name using a distinct option, I'd prefer specifying a network with the existing options, e.g. 10.1.2.0/24 - with the implementation then picking the local address found being inside that network.

For the deployment I'm planning, I have three types of boxes that all share the same network, but each type has a different interface naming convention.

[sean-]

@cruatta / @jness / @bof : Please give the latest code in master a twirl. The syntax for supporting IP addresses or getting the first "usable" IP address on an interface is included below and can be passed to any address parameter within Consul (e.g. -bind or bind_addr, or any other *_addr-like parameter):

-bind='{{ GetInterfaceIP "eth0" }}'
-bind='{{ GetAllInterfaces | include "network" "192.168.0.0/16" }}'

There is now a configurable template language for examples and docs) behind this that you can use to create a customizable heuristic that should allow you to get whatever it is that you need from your environment when using an immutable image (see hashicorp/go-sockaddr/template and cmd/sockaddr.