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Red Hat CoreOS

This tutorial will guide you through the basics of Red Hat CoreOS.

Red Hat CoreOS is the immutable, container-optimized operating system for OpenShift.

Accessing the host

To access the host, we will ssh into a master.

oc get nodes -l node-role.kubernetes.io/master -o wide

Select a machine, and export EXTERNAL_IP=<EXTERNAL IP>

To access the host:

ssh -i $PEM_FILE core@$EXTERNAL_IP
Red Hat CoreOS 4.0
 Information: https://url.corp.redhat.com/redhat-coreos
 Bugs: https://github.com/openshift/os

---

NOTE In the future, accessing a host via ssh will taint the node.

RHEL Kernel and Content

Red Hat CoreOS runs a RHEL kernel and uses RHEL content.

To view the RHEL kernel, execute the following command:

uname -rs
Linux 3.10.0-957.1.3.el7.x86_64

Ignition

Executes during early boot and writes files (regular files, systemd units, etc.) required to configure the host.

The configuration is served from the control plane.

Kubelet

The kubelet is packaged with the operating system. It is not run in a container. It is configured to use cri-o as the runtime.

To view status for kubelet, execute the following:

systemctl status kubelet -l
● kubelet.service - Kubernetes Kubelet
   Loaded: loaded (/etc/systemd/system/kubelet.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2018-12-03 19:49:15 UTC; 49min ago
  Process: 4104 ExecStartPre=/bin/mkdir --parents /etc/kubernetes/manifests (code=exited, status=0/SUCCESS)
 Main PID: 4124 (hyperkube)
   Memory: 161.9M
   CGroup: /system.slice/kubelet.service
           └─4124 /usr/bin/hyperkube kubelet --config=/etc/kubernetes/kubelet.conf --bootstrap-kubeconfig=/etc/kubernetes/kubeconfig --rotate-certificates --kubeconfig=/var/lib/kubelet/kubeconfig --container-runtime=remote --container-runtime-endpoint=/var/run/crio/crio.sock --allow-privileged --node-labels=node-role.kubernetes.io/master --minimum-container-ttl-duration=6m0s --client-ca-file=/etc/kubernetes/ca.crt --cloud-provider=aws --anonymous-auth=false --register-with-taints=node-role.kubernetes.io/master=:NoSchedule

CRI-O

Container runtime for Kubernetes. To view status for cri-o, execute the following:

systemctl status crio
● crio.service - Open Container Initiative Daemon
   Loaded: loaded (/usr/lib/systemd/system/crio.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2018-12-03 19:48:28 UTC; 49min ago
     Docs: https://github.com/kubernetes-sigs/cri-o
 Main PID: 4268 (crio)
   Memory: 3.4G
   CGroup: /system.slice/crio.service
           └─4268 /usr/bin/crio --cni-config-dir=/etc/kubernetes/cni/net.d --cni-plugin-dir=/var/lib/cni/bin

Inspected and debugged via crictl

To view running pods via crictl, execute the following:

 sudo crictl pods

Podman

Executes containers required to bring up a cluster on bootstrap machine.

To view containers, execute the following command:

sudo podman ps

Next

In the next step, we will explore how OpenShift nodes are configured via an operator.

Next: Maching Config