- As [@jaredallard](https://github.com/jaredallard) [pointed out](https://github.com/k3d-io/k3d/pull/48), people running `k3d` on a system with **btrfs**, may need to mount `/dev/mapper` into the nodes for the setup to work.
- k3s currently has [no support for ZFS](https://github.com/rancher/k3s/issues/66) and thus, creating multi-server setups (e.g. `#!bash k3d cluster create multiserver --servers 3`) fails, because the initializing server node (server flag `--cluster-init`) errors out with the following log:
starting kubernetes: preparing server: start cluster and https: raft_init(): io: create I/O capabilities probe file: posix_allocate: operation not supported on socket
```
- This issue can be worked around by providing docker with a different filesystem (that's also better for docker-in-docker stuff).
- A possible solution can be found here: [https://github.com/rancher/k3s/issues/1688#issuecomment-619570374](https://github.com/rancher/k3s/issues/1688#issuecomment-619570374)
- **Note**: There are many ways to use the `"` and `'` quotes, just be aware, that sometimes shells also try to interpret/interpolate parts of the commands
## How to access services (like a database) running on my Docker Host Machine
- As of version v3.1.0, we're injecting the `host.k3d.internal` entry into the k3d containers (k3s nodes) and into the CoreDNS ConfigMap, enabling you to access your host system by referring to it as `host.k3d.internal`
Some can be fixed by passing the `HTTP_PROXY` environment variables to k3d, some have to be fixed in docker's `daemon.json` file and some are as easy as adding a volume mount.
Failed to create pod sandbox: rpc error: code = Unknown desc = failed to get sandbox image "docker.io/rancher/pause:3.1": failed to pull image "docker.io/rancher/pause:3.1": failed to pull and unpack image "docker.io/rancher/pause:3.1": failed to resolve reference "docker.io/rancher/pause:3.1": failed to do request: Head https://registry-1.docker.io/v2/rancher/pause/manifests/3.1: x509: certificate signed by unknown authority
- Problem: inside the container, the certificate of the corporate proxy cannot be validated
- Possible Solution: Mounting the CA Certificate from your host into the node containers at start time via `k3d cluster create --volume /path/to/your/certs.crt:/etc/ssl/certs/yourcert.crt`
- When you perform cluster create and deletion operations multiple times with **same cluster name** and **shared volume mounts**, it was observed that `grep k3d /proc/*/mountinfo` shows many spurious entries
- Problem: Due to above, at times you'll see `no space left on device: unknown` when a pod is scheduled to the nodes
- If you observe anything of above sort you can check for inaccessible file systems and unmount them by using below command (note: please remove `xargs umount -l` and check for the diff o/p first)
- As per the conversation on [k3d-io/k3d#594](https://github.com/k3d-io/k3d/issues/594#issuecomment-837900646) above issue wasn't reported/known earlier and so there are high chances that it's not universal.
- When: This happens when running k3d on a Linux system with a kernel version >= 5.12.2 (and others like >= 5.11.19) when creating a new cluster
- the node(s) stop or get stuck with a log line like this: `<TIMESTAMP> F0516 05:05:31.782902 7 server.go:495] open /proc/sys/net/netfilter/nf_conntrack_max: permission denied`
- Why: The issue was introduced by a change in the Linux kernel ([Changelog 5.12.2](https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.12.2): [Commit](https://github.com/torvalds/linux/commit/671c54ea8c7ff47bd88444f3fffb65bf9799ce43)), that changed the netfilter_conntrack behavior in a way that `kube-proxy` is not able to set the `nf_conntrack_max` value anymore
- **Note**: k3d v4.4.5 already uses rancher/k3s:v1.21.1-k3s1 as the new default k3s image, so no workarounds needed there!
This is going to be fixed "upstream" in k3s itself in [rancher/k3s#3337](https://github.com/k3s-io/k3s/pull/3337) and backported to k3s versions as low as v1.18.
- **The fix was released and backported in k3s, so you don't need to use the workaround when using one of the following k3s versions (or later ones)**
You're deploying something to the cluster using an image from DockerHub and the image fails to be pulled, with a `429` response code and a message saying `You have reached your pull rate limit. You may increase the limit by authenticating and upgrading`.
### Cause
This is caused by DockerHub's pull rate limit (see <https://docs.docker.com/docker-hub/download-rate-limit/>), which limits pulls from unauthenticated/anonymous users to 100 pulls per hour and for authenticated users (not paying customers) to 200 pulls per hour (as of the time of writing).
### Solution
a) use images from a private registry, e.g. configured as a pull-through cache for DockerHub
b) use a different public registry without such limitations, if the same image is stored there
c) authenticate containerd inside k3s/k3d to use your DockerHub user
#### (c) Authenticate Containerd against DockerHub
1. Create a registry configuration file for containerd:
3. Profit. That's it. In the test for this, we pulled the same image 120 times in a row (confirmed, that pull numbers went up), without being rate limited (as a non-paying, normal user)
Longhorn is not working when deployed in a K3s cluster spawned with k3d.
### Cause
The container image of K3s is quite limited and doesn't contain the necessary libraries. Also, additional volume mounts and more would be required to get Longhorn up and running properly.
So basically Longhorn does rely too much on the host OS to work properly in the dockerized environment without quite some modifications.
### Solution
There are a few ways one can build a working image to use with k3d.
See <https://github.com/k3d-io/k3d/discussions/478> for more info.