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diff --git a/kubernetes.md b/kubernetes.md new file mode 100644 index 000000000..a88a76a38 --- /dev/null +++ b/kubernetes.md @@ -0,0 +1,105 @@ +# Running CRI-O on kubernetes cluster + +## Switching runtime from docker to CRI-O + +In standard docker kubernetes cluster, kubelet is running on each node as systemd service and is taking care of communication between runtime and api service. +It is reponsible for starting microservices pods (such as `kube-proxy`, `kubedns`, etc. - they can be different for various ways of deploying k8s) and user pods. +Configuration of kubelet determines which runtime is used and in what way. + +Kubelet itself is executed in docker container (as we can see in `kubelet.service`), but, what is important, **it's not** a kubernetes pod (at least for now), +so we can keep kubelet running inside container (as well as directly on the host), and regardless of this, run pods in chosen runtime. + +Below, you can find an instruction how to switch one or more nodes on running kubernetes cluster from docker to CRI-O. + +### Preparing crio + +You must prepare and install `crio` on each node you would like to switch. Here's the list of files that must be provided: + +| File path | Description | Location | +|--------------------------------------------|----------------------------|-----------------------------------------------------| +| `/etc/crio/crio.conf` | crio configuration | Generated on cri-o `make install` | +| `/etc/crio/seccomp.conf` | seccomp config | Example stored in cri-o repository | +| `/etc/containers/policy.json` | containers policy | Example stored in cri-o repository | +| `/bin/{crio, runc}` | `crio` and `runc` binaries | Built from cri-o repository | +| `/usr/local/libexec/crio/conmon` | `conmon` binary | Built from cri-o repository | +| `/opt/cni/bin/{flannel, bridge,...}` | CNI plugins binaries | Can be built from sources `containernetworking/cni` | +| `/etc/cni/net.d/10-mynet.conf` | Network config | Example stored in [README file](README.md) | + +`crio` binary can be executed directly on host, inside the container or in any way. +However, recommended way is to set it as a systemd service. +Here's the example of unit file: + +``` +# cat /etc/systemd/system/crio.service +[Unit] +Description=CRI-O daemon +Documentation=https://github.com/kubernetes-incubator/cri-o + +[Service] +ExecStart=/bin/crio --runtime /bin/runc --log /root/crio.log --log-level debug +Restart=always +RestartSec=10s + +[Install] +WantedBy=multi-user.target +``` + +### Preparing kubelet +At first, you need to stop kubelet service working on the node: +``` +# systemctl stop kubelet +``` +and stop all kubelet docker containers that are still runing. + +``` +# docker stop $(docker ps | grep k8s_ | awk '{print $1}') +``` + +We have to be sure that `kubelet.service` will start after `crio.service`. +It can be done by adding `crio.service` to `Wants=` section in `/etc/systemd/system/kubelet.service`: + +``` +# cat /etc/systemd/system/kubelet.service | grep Wants +Wants=docker.socket crio.service +``` + +If you'd like to change the way of starting kubelet (e.g. directly on host instead of docker container), you can change it here, but, as mentioned, it's not necessary. + + +Kubelet parameters are stored in `/etc/kubernetes/kubelet.env` file. +``` +# cat /etc/kubernetes/kubelet.env | grep KUBELET_ARGS +KUBELET_ARGS="--pod-manifest-path=/etc/kubernetes/manifests +--pod-infra-container-image=gcr.io/google_containers/pause-amd64:3.0 +--cluster_dns=10.233.0.3 --cluster_domain=cluster.local +--resolv-conf=/etc/resolv.conf --kubeconfig=/etc/kubernetes/node-kubeconfig.yaml +--require-kubeconfig" +``` + +You need to add following parameters to `KUBELET_ARGS`: +* `--experimental-cri=true` - Use Container Runtime Interface. Will be true by default from kubernetes 1.6 release. +* `--container-runtime=remote` - Use remote runtime with provided socket. +* `--container-runtime-endpoint=/var/run/crio.sock` - Socket for remote runtime (default `crio` socket localization). +* `--runtime-request-timeout=10m` - Optional but useful. Some requests, especially pulling huge images, may take longer than default (2 minutes) and will cause an error. + +Kubelet is prepared now. + +## Flannel network +If your cluster is using flannel network, your network configuration should be like: +``` +# cat /etc/cni/net.d/10-mynet.conf +{ + "name": "mynet", + "type": "flannel" +} +``` +Then, kubelet will take parameters from `/run/flannel/subnet.env` - file generated by flannel kubelet microservice. + +## Starting kubelet with CRI-O +Start crio first, then kubelet. If you created `crio` service: +``` +# systemctl start crio +# systemctl start kubelet +``` + +You can follow the progress of preparing node using `kubectl get nodes` or `kubectl get pods --all-namespaces` on kubernetes master. |