About one year ago I have written an article on how to get Racher running in an LXC container on a Proxmox node. I managed to get it running and described the required steps in this article.

What I did not manage to get running was adding a cluster in Rancher using LXC nodes. I left the topic aside and moved on to other things. I had a lot of other projects in the meantime with Rachner and Kubernetes in general, and now wanted to finally start using it for my own infrastructure.

Sure I could have accepted that Kubernetes is not running in LXC and used KVM based nodes to run a cluster. But I did not. There must be a way. Others are running Kubernetes as well in LXC containers. And resource usage, as well as backup is so much more efficient when using LXC containers.

No final success (yet)

Before you expect to find the final solution in this blog post, I must disappoint you. I have solved a few problems so far but still did not manage to bring up a final cluster (yet). If you have any ideas after reading this, how to get it done, please let me know.

The problem I was facing at the end is, that I was stuck at the error “network plugin is not ready: cni config uninitialized”.

The reason for the problems

The main difference between KVM and LXC is that containers are sharing the kernel with the host. Also there is no virtualization of devices. It behaves more like an advanced chroot. This means access to /proc, /sys and /dev is limited. Additionally the container lacks a lot of kernel capabilities by default. Loading of kernel modules cannot be done inside of the container, but rather needs to be done on the host.

Docker requirements

Ranchers RKE1 (which is still the only available stable version as of the date of this post), is still using docker as container runtime, even though this has been deprecated by the Kubernetes project. But as this is still the case, we need to meat the docker requirements first, in order to proceed to the next step.

Docker requires a few kernel modules to be enabled. Those are overlayfs and aufs. We will see some other required kernel modules later on as well, but lets keep it to those for now. Docker normally would load the modules for us, but as this is not permitted within the LXC container, we need to do it ourself.

Executing following commands should do the trick.

modprobe aufs
modprobe overlay

To ensure they are loaded on boot of the system the cleanest way is to create a file in /etc/modules-load.d.

cat > /etc/modules-load.d/docker.conf <<EOF

Now let’s create a container on the proxmox host. In my case it has the id 100, is using Ubuntu 20.04 as base image, has mgmt1.n.dev.localhost as hostname. Make sure to adjust the network configuration to your network.

pct create 100 local:vztmpl/ubuntu-20.04-standard_20.04-1_amd64.tar.gz --cores 4 --memory 4096 --swap 2048 --hostname mgmt1.n.dev.localhost --rootfs local:20 --net0 name=eth0,ip=,bridge=vmbr10,gw= --onboot 1

In order to run docker inside of the container, the container needs to be privileged. This is the case, if you don’t especially create the containers as unprivileged in Proxmox. This alone does not give us enough permissions, we need to enable the nesting feature in LXC as well.

pct set 100 --features nesting=1

Now we should be able to start the container, enter it, install docker and run a hello-world container.

As we don’t want the container to be accessible using ssh and only use it as docker host, we remove some unnecessary packages. Please note that the removal of apparmor is required as well.

pct start 100
pct enter 100
apt-get -y remove openssh-server postfix accountsservice networkd-dispatcher rsyslog cron dbus apparmor
wget -O - https://releases.rancher.com/install-docker/20.10.sh | sh

Please note that we install docker using the script provided by Rancher, to have be compatible with the Kubernetes version we want to install. Feel free to check the script before you just dump it into sh. If you don’t want to use Kubernetes you can also install the docker.io package from distribution repositories.

Now docker run hello-world should give you:

root@mgmt1:~# docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
2db29710123e: Pull complete 
Digest: sha256:4c5f3db4f8a54eb1e017c385f683a2de6e06f75be442dc32698c9bbe6c861edd
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
 $ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:

For more examples and ideas, visit:

Running docker containers is not enough

At some point in the rancher setup, after you have created a cluster and want to add nodes to it, you are asked to execute something like this on the node, to bootstrap the cluster.

docker run -d --privileged --restart=unless-stopped --net=host -v /etc/kubernetes:/etc/kubernetes -v /var/run:/var/run  rancher/rancher-agent:v2.6.3 --server https://rancher.localhost --token <some token> --etcd --controlplane --worker

This basically creates a new container running rancher-agent, giving it full access to the docker daemon by mounting /var/run/docker.sock. This lets rancher-agent start new containers with the Kubernetes processes on the node.

Normally you would now grab a coffee and wait 10 to 15 minutes for the node to become alive. But it’s not time for coffee yet.

You will notice that the bootstrapping of the cluster now would fail. The LXC container need more capabilities, and permissions and modules.

I did some research on the internet and adding a few lines to the LXC config, and a few modules should do the trick.

modprobe ip_vs
modprobe ip_vs_rr
modprobe ip_vs_wrr
modprobe ip_vs_sh
modprobe nf_conntrack
modprobe br_netfilter
modprobe rbd
cat >> /etc/pve/lxc/100.conf <<EOF
lxc.apparmor.profile: unconfined
lxc.cgroup.devices.allow: a
lxc.mount.auto: "proc:rw sys:rw"
cat >> /etc/modules-load.d/docker.conf <<EOF
pct stop 100
pct start 100

Now bootstraping fails because / is not shared. Ok the quick fix is to run mount --make-rshared / in the container.

But still, bootstrapping the node gives me some error like [controlPlane] Failed to upgrade Control Plane: [[host mgmt1 not ready]].

After running docker ps on the node, I noticed on container in state restarting. Looking into the logs of this container, we notice that it did not start because /dev/kmsg is not available.

The problem seems familiar, as it was the same problem we had wen running Rancher in LXC. So I tried the same fix, we did there.

lxc.mount.entry: /dev/kmsg dev/kmsg none defaults,bind,create=file

Problem seems that now /dev/kmsg exists, but is not readable. I did not managed to solve this problem, but found a workaround that seems to be sufficient. Linking /dev/kmsg to /dev/console.

So now lets make those changes persistent. Applying those changes on boot using rc.local is not pretty, but should do the job.

cat > /etc/rc.local <<EOF
#!/bin/sh -e

if [ ! -e /dev/kmsg ]; then
    ln -s /dev/console /dev/kmsg

mount --make-rshared /
chmod +x /etc/rc.local

Access to sysctl

Even after those changes, we see one container failing. Looking into it, you see that Kubernetes wants to change net.netfilter.nf_conntrack_max, as the value configured by default in Proxmox is too low.

In my case I had to change it to at least 786432. The strange thing is, I thought that using proc:rw sys:rw would allow write access to those settings. But this seems not to be the case. Those need to be changed on the host.

I changed the value and tried again. Long story short, those are the settings that need to be changed:

cat > /etc/sysctl.d/100-docker.conf  <<EOF
cat >> /etc/modules-load.d/docker.conf <<EOF
options nf_conntrack hashsize=196608

Networking problems

After all those changes, in my trys I was stuck at the Problem “network plugin is not ready: cni config uninitialized”. The directory /etc/cni/net.d on the node (which is mapped into the containers), has not been created. I tried all network plugins rancher provided in different versions.

Well, I leave it to this for now.