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About CRI-O container runtime engine

CRI-O is a Kubernetes-native container runtime implementation that integrates closely with the operating system to deliver an efficient and optimized Kubernetes experience. CRI-O provides facilities for running, stopping, and restarting containers.

The CRI-O container runtime engine is managed using a systemd service on each OpenShift Container Platform cluster node. When container runtime issues occur, verify the status of the crio systemd service on each node. Gather CRI-O journald unit logs from nodes that manifest container runtime issues.

Verifying CRI-O runtime engine status

You can verify CRI-O container runtime engine status on each cluster node.

Prerequisites
  • You have access to the cluster as a user with the cluster-admin role.

  • You have installed the OpenShift CLI (oc).

Procedure
  1. Review CRI-O status by querying the crio systemd service on a node, within a debug pod.

    1. Start a debug pod for a node:

      $ oc debug node/my-node
    2. Set /host as the root directory within the debug shell. The debug pod mounts the host’s root file system in /host within the pod. By changing the root directory to /host, you can run binaries contained in the host’s executable paths:

      # chroot /host

      OpenShift Container Platform 4.7 cluster nodes running Red Hat Enterprise Linux CoreOS (RHCOS) are immutable and rely on Operators to apply cluster changes. Accessing cluster nodes using SSH is not recommended and nodes will be tainted as accessed. However, if the OpenShift Container Platform API is not available, or the kubelet is not properly functioning on the target node, oc operations will be impacted. In such situations, it is possible to access nodes using ssh core@<node>.<cluster_name>.<base_domain> instead.

    3. Check whether the crio systemd service is active on the node:

      # systemctl is-active crio
    4. Output a more detailed kubelet.service status summary:

      # systemctl status crio

Gathering CRI-O journald unit logs

If you experience CRI-O issues, you can obtain CRI-O journald unit logs from a node.

Prerequisites
  • You have access to the cluster as a user with the cluster-admin role.

  • Your API service is still functional.

  • You have installed the OpenShift CLI (oc).

  • You have the fully qualified domain names of the control plane, or control plane machines (also known as the master machines).

Procedure
  1. Gather CRI-O journald unit logs. The following example collects logs from all control plane nodes (within the cluster:

    $ oc adm node-logs --role=master -u crio
  2. Gather CRI-O journald unit logs from a specific node:

    $ oc adm node-logs <node_name> -u crio
  3. If the API is not functional, review the logs using SSH instead. Replace <node>.<cluster_name>.<base_domain> with appropriate values:

    $ ssh core@<node>.<cluster_name>.<base_domain> journalctl -b -f -u crio.service

    OpenShift Container Platform 4.7 cluster nodes running Red Hat Enterprise Linux CoreOS (RHCOS) are immutable and rely on Operators to apply cluster changes. Accessing cluster nodes using SSH is not recommended and nodes will be tainted as accessed. Before attempting to collect diagnostic data over SSH, review whether the data collected by running oc adm must gather and other oc commands is sufficient instead. However, if the OpenShift Container Platform API is not available, or the kubelet is not properly functioning on the target node, oc operations will be impacted. In such situations, it is possible to access nodes using ssh core@<node>.<cluster_name>.<base_domain>.

Cleaning CRI-O storage

You can manually clear the CRI-O ephemeral storage if you experience the following issues:

  • A node cannot run on any pods and this error appears:

    Failed to create pod sandbox: rpc error: code = Unknown desc = failed to mount container XXX: error recreating the missing symlinks: error reading name of symlink for XXX: open /var/lib/containers/storage/overlay/XXX/link: no such file or directory
  • You cannot create a new container on a working node and the “can’t stat lower layer” error appears:

    can't stat lower layer ...  because it does not exist.  Going through storage to recreate the missing symlinks.
  • Your node is in the NotReady state after a cluster upgrade or if you attempt to reboot it.

  • The container runtime implementation (crio) is not working properly.

  • You are unable to start a debug shell on the node using oc debug node/<nodename> because the container runtime instance (crio) is not working.

Follow this process to completely wipe the CRI-O storage and resolve the errors.

Prerequisites:
  • You have access to the cluster as a user with the cluster-admin role.

  • You have installed the OpenShift CLI (oc).

Procedure
  1. Use cordon on the node. This is to avoid any workload getting scheduled if the node gets into the Ready status. You will know that scheduling is disabled when SchedulingDisabled is in your Status section:

    $ oc adm cordon <nodename>
  2. Drain the node as the cluster-admin user:

    $ oc adm drain <nodename> --ignore-daemonsets --delete-local-data
  3. When the node returns, connect back to the node via SSH or Console. Then connect to the root user:

    $ ssh core@node1.example.com
    $ sudo -i
  4. Manually stop the kubelet:

    # systemctl stop kubelet
  5. Stop the containers and pods:

    # crictl rmp -fa
  6. Manually stop the crio services:

    # systemctl stop crio
  7. After you run those commands, you can completely wipe the ephemeral storage:

    # crio wipe -f
  8. Start the crio and kubelet service:

    # systemctl start crio
    # systemctl start kubelet
  9. You will know if the clean up worked if the crio and kubelet services are started, and the node is in the Ready status:

    $ oc get nodes
    Example output
    NAME				    STATUS	                ROLES    AGE    VERSION
    ci-ln-tkbxyft-f76d1-nvwhr-master-1  Ready, SchedulingDisabled   master	 133m   v1.22.0-rc.0+75ee307
  10. Mark the node schedulable. You will know that the scheduling is enabled when SchedulingDisabled is no longer in status:

    $ oc adm uncordon <nodename>
    Example output
    NAME				     STATUS	      ROLES    AGE    VERSION
    ci-ln-tkbxyft-f76d1-nvwhr-master-1   Ready            master   133m   v1.22.0-rc.0+75ee307