Running Krustlet on MicroK8s

These are steps for running Krustlet node(s) and MicroK8s on the same machine.

Prerequisites

You will require a running MicroK8s cluster for this guide. The steps below assume you will run MicroK8s and the Krustlet, on a single machine. kubectl is required but is installed with MicroK8s as microk8s.kubectl. The following instructions use microk8s.kubectl for simplicity. You may use a standlone kubectl if you prefer.

In order for the bootstrap authentication token to work, your kube-apiserver needs to have the --enable-bootstrap-token-auth feature flag enabled. See bootstrap-tokens for more information.

To verify you have the bootstrap authentication feature enabled, check the process args:

$ ps -ef | grep kube-apiserver | grep "enable-bootstrap-token-auth"

If it doesn’t show up and you installed using snap, you can find the startup args in /var/snap/microk8s/current/args/kube-apiserver and add the flag.

Now you need to restart the kube-apiserver with the command:

$ systemctl restart snap.microk8s.daemon-apiserver

Step 1: Get a bootstrap config

Krustlet requires a bootstrap token and config the first time it runs. Follow the guide here to generate a bootstrap config and then return to this document. This will If you already have a kubeconfig available that you generated through another process, you can proceed to the next step. However, the credentials Krustlet uses must be part of the system:nodes group in order for things to function properly.

NOTE You should now have a file bootstrap.conf in ${HOME}/.krustlet/config

Step 2: Install and configure Krustlet

Install the latest release of Krustlet following the install guide.

Let’s use the built in krustlet-wasi provider

$ ./KUBECONFIG=${PWD}/krustlet-config \
  krustlet-wasi \
  --node-ip=127.0.0.1 \
  --node-name=krustlet \
  --bootstrap-file=${HOME}/.krustlet/config/bootstrap.conf

NOTE: To avoid the Krustlet using your default Kubernetes credentials (~/.kube/config), it is a good idea to override the default value here using KUBECONFIG. For bootstrapping, KUBECONFIG must point to a non-existent file (!). Bootstrapping will write a new configuration file to this location for you. NOTE: If you receive an error that the CSR already exists, you may safely delete the existing CSR (kubectl delete csr <hostname>-tls) and try again.

Step 2a: Approving the serving CSR

Once you have started Krustlet, there is one more manual step (though this could be automated depending on your setup) to perform. The client certs Krustlet needs are generally approved automatically by the API. However, the serving certs require manual approval. To do this, you’ll need the hostname you specified for the --hostname flag or the output of hostname if you didn’t specify anything. From another terminal that’s configured to access the cluster, run:

$ microk8s.kubectl certificate approve <hostname>-tls

NOTE: You will only need to do this approval step the first time Krustlet starts. It will generate and save all of the needed credentials to your machine

Step 3: Test that things work

Now you can see things work! Feel free to give any of the demos a try in another terminal like so:

$ microk8s.kubectl apply --filename=https://raw.githubusercontent.com/krustlet/krustlet/main/demos/wasi/hello-world-rust/k8s.yaml
$ microk8s.kubectl logs pod/hello-world-wasi-rust
hello from stdout!
hello from stderr!
POD_NAME=hello-world-wasi-rust
FOO=bar
CONFIG_MAP_VAL=cool stuff
Args are: []

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