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Using an OVH dedicated server to host VMs with public IPs

Using an OVH dedicated server to host VMs with public IPs is not hard if you know how, otherwise it can be a hellish nightmare!

Here's my little story with OVH's poorly maintained guide...



Updating the hard way

I recently learnt the hard way that iproute2 was replacing a lot of deprecated tools... So you have a bunch of things that you can't rely on anymore, depending on which Linux distribution you're using. Some dropped ifconfig. Interface names have become better, predictable, and deprecated good old eth0; so now you have eno1 or ens1 and that made me kinda angry at first because I didn't know what "predictable" meant there, since for me eth0 for the first interface found was more "predictable" than some randomy name starting with an e followed by surprise letters and numbers! Then I read about those predictable names and understood they actually made sense! And I understood why I was out of the loop! It was created in 2009 and my networking knowledge hadn't had much update between 2009 and 2019!

/etc/network/interfaces on Ubuntu is deprecated, you have to look at /etc/netplan instead.

ifconfig doesn't work on Arch Linux (I think you can still install it, but why install a deprecated tool?)


Then you have a lot of documentation that is more or less up to date. And you have that awful name for this new iproute2 tool: ip!!! Yes it's convenient to have a short name for a tool, yes this name totally makes sense. HOWEVER ip is the WORST command name if you're looking for information on Google! Okay, it might not be the worst... X isn't (wouldn't be) any better! So instead of searching ip, you have to add iproute2, hoping that the people who write about that command will mention iproute2 (like I'm doing here, haha).

Arch Linux vs Ubuntu

Bias for Ubuntu

I prefer Ubuntu because it's simpler, so many things are done for you! But then, you might argue that Ubuntu is heavy... And it certainly has become extra heavy! So heavy that for some obscure reasons, when I use Ubuntu for hosting virtual machines (VMs), it just doesn't work for me! I'm mainly a macOS user on a daily basis. But I do use Linux, from a little to a lot, but generally without a graphical user interface (GUI). But to manage VMs (creations, deletions, modifications, etc.), I don't wanna do it without a GUI because it's complicated, error-prone, and it's very useless unless you're mass-producing VMs, in which case it's mandatory to drop the GUI (or just use it to make your genesis template and then forget about it).

But Arch Linux wins

So, I used ssh -CY to connect to the host and then I use virt-manager. But when the host is Ubuntu, it's unusable under macOS. It's kinda usable when the client is a Linux as well, so I booted a Live Ubuntu using a USB key on a MacBook to have a Linux. But that's very inconvenient!

And at some point I tried Arch Linux for the host and surprisingly now I can use macOS to ssh -CY to the Arch Linux and launch virt-manager and it's quite usable!

I don't know why, I don't wanna investigate why, but I'm kinda happy I found that solution. I'm guessing of course that it's all because Arch Linux is lighter. But I really don't know why. Just like I don't know why Arch Linux's pacman will install packages much much much faster than Ubuntu's apt. That's not my problem! I can't make every little problem my own, there are too many! haha


For some reason, I couldn't get the network work without a NAT. Everytime I used a bridge, either it would make the VM lose its connection or worse, the host to become unreachable!

Long story short, now... here's the deal:

On the host

Just create your VMs. Use NAT. When the VMs are ready, add a bridge interface (hotplug should be fine, I never had to reboot the VMs). Select the host interface that has the internet. If your host uses Arch Linux, it's likely to be eno1, in which case select Host device eno1: macvtap. Enter the MAC address that OVH generated for your failover IP. If you don't have one... I actually don't know if it's necessary! About 10 years ago, it wasn't. But if it is and you don't have it, go to your OVH "manager" and get one! Actually I expected OVH to provide DHCP for the VM using the bridge; but it has never DHCPed for me so when I have time I'll try without setting the MAC address on the OVH manager side. Anyway, here's a screenshot, it might help:


As soon as you create the interface, it should become available on your VM. (It'll also appear on the host but that doesn't matter.)

Configure your VM's new network interface

If you used the NAT, the good thing is that there's already a working connection on your VM so you can do it via SSH. But if you make sure you still have a VNC access to your VM, it'll help in case you mess up and your VM becomes unreachable!

So... I used OVH's documentation but either because I'm bad at following the steps and/or because it's just outdated, it never worked for me.

Once the new network interface is added, I create a 3-line script that I'll use everytime I need to connect the failover IP to my VM.

Arch Linux VM

Run this script as user root if your new network interface is ens3, otherwise replace it by the proper name!

ip address add $FAILOVER_IP broadcast $FAILOVER_IP dev ens3
ip route add $HOST_GATEWAY_IP dev ens3
ip route add default via $HOST_GATEWAY_IP

where $FAILOVER_IP has to be replaced by your failover IP; and $HOST_GATEWAY_IP is basically your host's IP where you replace the last part with 254.

Ubuntu VM

Run this script as a sudoer if your new network interface is ens9, otherwise replace it by the proper name!

sudo ifconfig ens9 $FAILOVER_IP netmask broadcast $FAILOVER_IP
sudo route add $HOST_GATEWAY_IP dev ens9
sudo route add default gw $HOST_GATEWAY_IP

And then see if your $FAILOVER_IP is pingable!


Once you have something that works...

it's easier to get to the clean way of doing it!

That "shortcut" solution that I give you here is not a very good way of doing things! Everytime you boot your VM, you have to reconfigure your interface...

But hopefully this will be useful to some people...

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