Use Google BBR as the default TCP congestion control

[jigsaw-code]

Use Google BBR as the default TCP congestion control

DigitalOcean has updated their images to include Ubuntu 18.04, which ships with kernel 4.15, so we've modified the installation script for DigitalOcean servers to enable BBR by default. Note that this doesn't affect 'advanced installation' servers yet, though we plan to do that too (with the caveat that we'll only do it if the Kernel already supports BBR, rather than attempt patching it or upgrading it).

[tobyxdd]

Docker containers don't have their own TCP/IP stacks. The install script has to enable BBR on the host (if it's available).

[fortuna]

Thanks for the suggestion.

Unfortunately the kernel of our image is 4.4, so it doesn't come with BBR

# sysctl net.ipv4.tcp_available_congestion_control
net.ipv4.tcp_available_congestion_control = cubic reno

We'll investigate how easy it is to use a different kernel. Any guidance is appreciated.

[fortuna]

Ok, I learned that Docker actually uses the host kernel. So there's no way in our docker image to guarantee the use of BBR.

I guess we can enhance the install script to check if BBR support is available, and enable it if so.

[OneHappyForever]

It should work on KVM vps, like digitalocean. It will NOT work on openvz.

However, based on my personal testing, I HIGHLY recommend implementing this feature.

[trevj]

Related performance issue:
#63

[jab]

When calling the DO API to create the host VM, could the OS be switched from Ubuntu to DO’s Debian 9 image? Looks like that comes with the 4.9 kernel by default.

[jab]

Or maybe switching to Ubuntu 18.04 LTS when it comes out later this month is the better move. That has the 4.15 kernel by default.

[fortuna]

Those are good ideas. However they don't come with Docker pre-installed, and installing it significantly increased the server creation time the last time we tried.

Ideally DO would update the docker image to have the latest kernel

[jab]

For sure. (And if we haven't already maybe let's open a DO support request for this and/or write to the DO user forums.)

In the meantime though, for affected users I can imagine it being well worth it to grab a coffee during a longer server creation step in return for actually getting a usable proxy at the end.

Another idea could be including a

[ ] Use BBR for better connectivity from China / lossy networks
    (increases setup time by 5 minutes)

checkbox, possibly buried under an "advanced" section of the UI, during server creation.

I get the same speed with or without BBR, but I get higher speeds with KCP. Maybe we should use kcptun instead? It doesn't require replacing the kernel too.