Working in a really cool project with Clear ML, I had to figure out why it was not possible to install some Python packages from pypi. First feedback I received was “docker image has a bug”, but when I went deeper, I saw that behaviour was not related to the image, nvidia/cuda, or to the site, pypi. The strange behaviour affected, mainly but not always, to https, but also from other docker images: ubuntu, nginx, … Therefore, something was happening between the docker daemon and the virtual machine.

Containers were running into Genesis Cloud Ubuntu instances, so as first step, I check out the network interfaces:

$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc mq state UP group default qlen 1000
    link/ether 1b:36:33:cb:a5:f1 brd ff:ff:ff:ff:ff:ff
3: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default 
    link/ether 0e:22:c2:16:c4:7f brd ff:ff:ff:ff:ff:ff

As we can see, the network interface eth0 has a mtu (Maximum Transmission Unit) of 1450 when the Docker’s network bridge has a mtu of 1500 by default (and it is a common value). In order to make it work, network bridge’s mtu can not be greater than the physical one, therefore, we could set up docker0 to have a mtu of 1450 just customizing /etc/docker/daemon.json.


    // Other parameters
    "mtu": 1450

And restart your docker service:

$ sudo systemctl restart docker

Now, your containers will properly work.

Why does Genesis Cloud configure mtu to 1450 in their ubuntu instances? That’s a question for them ☺️.