Add support for http_interface

[alandsidel]

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Description

Some providers support http_interface in addition to the other http_ options. This is desirable functionality.

Use Case(s)

Packer is being run on disparate machines with multiple non-loopback interfaces that do not have static IPs, making use of http_bind_address cumbersome.

In particular this would be useful for users running packer on a machine that is sometimes on-prem and connected directly to the corporate network, and at other times is off-prem and connecting with a VPN tunnel.

Using http_bind_address as a workaround does work, but it's more cumbersome to look up your dynamic address each time than to simply enter the easy to remember name of the appropriate interface.

Potential configuration

As in existing plugins that support the feature

http_interface = "vmx0" // or tun0, eth0, ens160, etc.

Potential References

hashicorp/packer#10168

[alandsidel]

Upon further investigation, I believe that both options are present but simply being ignored. http_bind_address and http_interface can both be used in the configuration, and having both at the same time results in the same error as expected -- however regardless of what you set either one to, the plugin seems to ignore the setting and use the normal selection method.

In my test environment I have a Ubuntu 20 VM which has an address of 192.168.128.54/24 on eth0 and 192.168.122.16/24 on tun0. Setting http_interface = "tun0" or http_bind_address = "192.168.122.16" both result in the output during packer build of HTTP server is working at http://192.168.128.54:40251/

The http_port_min and http_port_max options are clearly working.

[alandsidel]

A bit of further investigation.

http_bind_address does seem to be working, and netstat -anl shows it listening on the specified address, even though the HTTP server is working at... message shows the wrong address. Unfortunately the incorrect address is not just being printed on the console, but is the address the remote side is being instructed to connect to.

Meanwhile, http_interface causes the module to listen on all interfaces rather than the specified one, which would work as a workaround if nothing else is using the port on any interface, but it only listens on the ipv6 socket.

[alandsidel]

Closed in favor of bug #247