Bind to specific output network interface and/or IP

Feature Request

For systems with multiple network interfaces (e.g., eth0 and VPN tun0) it could happen that Telegraf takes the wrong one, because sometimes the default routing is not the correct for Telegraf.

Proposal:

It should be possible to specify which network IP or network interface Telegraf should be using.

Current behavior:

Output plugin, e.g., InfluxDB, uses the first/default routing interface.

Desired behavior:

A configuration option "bind" or "interface" should be introduced allowing to specify which specific network interface "e.g., "tun0") or IP address Telegraf should be using.

Use case:

• Normally, Telegraf (LAN, Raspi) is sending metrics to an InfluxDB (Internet, VPS).
• However, sometimes I activate a VPN on the Raspi. Then there's an additional network interface (e.g., tun0) which becomes the default network gateway/routing.
• But, the VPS accepts only certain IPs (from my local network).
• So, Telegraf is collecting, it's sending, via tun0, but because this has the VPN IP, the collected data does not arrive the InfluxDB (on VPS) because of IP restrictions.

No implementation files or tests are named. Start by tracing how the InfluxDB output plugin establishes connections and reads configuration, then determine whether binding should apply to that output or to outputs generally. Done means a configuration option can select an interface or IP and the selected route is used reliably, with coverage for the supported behavior.