I was originally going to use GlusterFS to provide persistent storage
for pods, but [Heketi][0], the component that provides the API for
the Kubernetes StorageClass, is in "deep maintenance" status and looks
to be practically dead. I was a bit afraid to try to use it because of
that, and went looking for guidance on Reddit, which is how I discovered
Longhorn.
This manifest deploys the *ingress-nginx* controller, which is
responsible for handing traffic from clients outside the cluster and
routing it to the proper pods. I am using host network mode here to
avoid having to have another proxy in front of the ingress controller,
which would be required in NodePort mode.
I looked at MetalLB briefly, but decided to avoid it for now. As with
everything else in the Kubernetes world, it seems massively complex.
We're going to be using Longhorn for persistent storage. Longhorn
allocates space on worker nodes and exposes iSCSI LUNs to other worker
nodes. It creates sparse filesystem images under `/var/lib/longhorn`
for each volume. Thus, we need to mount a large filesystem at that
path on each worker node for Longhorn to use.
Using two different kickstart scripts, one for the control plane nodes,
and one for the worker nodes, we can properly mount the Longhorn data
directory only on machines that will be running the Longhorn manager.
Longhorn only supports *ext4* and *XFS* filesystem types.
* Correct example hostname
* Apply `base.yml` and `hostname.yml` separately, without
`bootstrap.yml`, to avoid deploying *firewalld*
* Correct host IP address
Kubernetes, or rather mostly Calico, does not play well on a machine
with an immutable root filesyste. Specifically, Calico needs write
access to a couple of paths on the root filesystem, such as
`/etc/cni/net.d`, `/opt/cni/bin`, and
`/usr/libexec/kubernetes/kubelet-plugins/volume`. Some of those paths
can be configured, but doing so is quite cumbersome. While these paths
could be made writable, e.g. using symlinks or bind mounts, it would add
a lot of complexity to the *kubelet* Ansible role. After considering
the options for a while, I decided that the best approach was probably
to mount specific filesystems at these paths. Instead of using small
LVM logical volumes for each one, I thought it would be better to use a
single *btrfs* filesystem for all the mutable storage locations. This
way, if I discover more paths that need to be writable, I can create
subvolumes for them, without having to try to move or resize the
existing volumes.
Now that the Kubernetes nodes need their own special kickstart file for
the disk layout, it also makes sense to handle the rest of the machine
setup there, too. This eliminates the need for the *kubelet* Ansible
role altogether. Any machine provisioned with this kickstart
configuration is immediately ready to become a Kubernetes control plane
or worker node.
Dustin