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FAQ / Nice to know

Issues with BTRFS

  • As @jaredallard pointed out, people running k3d on a system with btrfs, may need to mount /dev/mapper into the nodes for the setup to work.
  • This will do: k3d cluster create CLUSTER_NAME -v /dev/mapper:/dev/mapper

Issues with ZFS

  • k3s currently has no support for ZFS and thus, creating multi-server setups (e.g. 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

Pods evicted due to lack of disk space

  • Pods go to evicted state after doing X
  • Related issues: #133 - Pods evicted due to NodeHasDiskPressure (collection of #119 and #130)
  • Background: somehow docker runs out of space for the k3d node containers, which triggers a hard eviction in the kubelet
  • Possible fix/workaround by @zer0def:
    • use a docker storage driver which cleans up properly (e.g. overlay2)
    • clean up or expand docker root filesystem
    • change the kubelet’s eviction thresholds upon cluster creation: k3d cluster create --k3s-agent-arg '--kubelet-arg=eviction-hard=imagefs.available<1%,nodefs.available<1%' --k3s-agent-arg '--kubelet-arg=eviction-minimum-reclaim=imagefs.available=1%,nodefs.available=1%'

Restarting a multi-server cluster or the initializing server node fails

  • What you do: You create a cluster with more than one server node and later, you either stop server-0 or stop/start the whole cluster
  • What fails: After the restart, you cannot connect to the cluster anymore and kubectl will give you a lot of errors
  • What causes this issue: it’s a known issue with dqlite in k3s which doesn’t allow the initializing server node to go down
  • What’s the solution: Hopefully, this will be solved by the planned replacement of dqlite with embedded etcd in k3s
  • Related issues: #262

Passing additional arguments/flags to k3s (and on to e.g. the kube-apiserver)

  • The Problem: Passing a feature flag to the Kubernetes API Server running inside k3s.
  • Example: you want to enable the EphemeralContainers feature flag in Kubernetes
  • Solution: k3d cluster create --k3s-server-arg '--kube-apiserver-arg=feature-gates=EphemeralContainers=true'
  • Note: Be aware of where the flags require dashes (--) and where not.

    • the k3s flag (--kube-apiserver-arg) has the dashes
    • the kube-apiserver flag feature-gates doesn’t have them (k3s adds them internally)
  • Second example: k3d cluster create k3d-one --k3s-server-arg --cluster-cidr="" --k3s-server-arg --service-cidr="" --k3s-server-arg --disable=servicelb --k3s-server-arg --disable=traefik --verbose

  • 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

Running behind a corporate proxy

Running k3d behind a corporate proxy can lead to some issues with k3d that have already been reported in more than one issue. 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.

Pods fail to start: x509: certificate signed by unknown authority

  • Example Error Message: Failed to create pod sandbox: rpc error: code = Unknown desc = failed to get sandbox image "": failed to pull image "": failed to pull and unpack image "": failed to resolve reference "": failed to do request: Head 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
  • Issue: rancher/k3d#535

Last update: April 14, 2021