Question

Send outbound traffic over floating IP

Is it possible to route outbound traffic from a droplet through its floating IP. I.e., make http requests from the droplet that appear to originate from the floating IP?


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Accepted Answer

The short answer is yes. The longer answer is that it depends on the software you are using to make the request. It needs to expose some way of binding to a particular interface. If it does, you’ll need to find what we call the “anchor IP” and use it. The easiest way to find the anchor IP is to inspect your Droplet’s metadata. From the Droplet, run:

  1. curl -s http://169.254.169.254/metadata/v1/interfaces/public/0/anchor_ipv4/address

In my case, it returns 10.10.0.8 If you wanted to make your request with curl you could then use:

  1. curl --interface 10.10.0.8 https://example.com

Or with wget you would use:

  1. wget --bind-address=10.10.0.8 https://example.com

In both cases, example.com would now see the request as coming from my Floating IP not my Droplet’s IP address.

Check out this tutorial for more info on Floating IPs: How To Use Floating IPs on DigitalOcean In particular, see the section on “Droplet Anchor IPs.”

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The following worked for me on ubuntu:

Find the IPv4 gateway anchor:

curl -s http://169.254.169.254/metadata/v1/interfaces/public/0/anchor_ipv4/gateway | xargs route add default gw

If you’re concerned about copy / pasting random things (and you should be); the Floating IP gateway documentation can be found here:

https://developers.digitalocean.com/documentation/metadata/#interface-anchor_ipv4-gateway

It’s crazy that I would think this would be such an essential, important feature of floating ips and yet it’s nearly impossible. After fighting this for about 2 or 3 ours on Ubuntu (Tried pretty much everything here, I could not get it to work).

What I ended up doing is using Squid proxy to handle this. If anyone is interested, here’s a bash script to setup Squid locally (with authentication) and have it route traffic through the floating IP (the line with tcp_outgoing_address $GATEWAY ev is basically where the magic happens).

Hopefully DO can shed some light on how to do this properly soon.

@ComputerUser I was on 18.10 I believe when I was trying this. However as I could not get system services to use the floating IP I gave up on it and switched back to the main IP. It would have saved so much time not having to update DNS on a load of domains and just switch the floating IP between servers but when your email is being received on the floating IP but sent out on the main IP this does not work and leads to the mail server being blacklisted. DO did agree it was too difficult to work with floating IPs and recommended giving up on them until they worked better (e.g. so the server saw it as the primary IP ). Floating IPs could be a great feature for disaster recovery features (i.e. switch the IP from one server to another without having to edit a load of DNS entries and wait for the cache to update) but it seems they are not there yet.