Version 1.6. This version is supported as outlined in the Anthos version support policy, offering the latest patches and updates for security vulnerabilities, exposures, and issues impacting Anthos clusters on bare metal. For more details, see the release notes 1.6. This is not the most recent version. For a complete list of each minor and patch release in chronological order, see the combined release notes.

Available versions: 1.8  |   1.7  |   1.6

Anthos clusters on bare metal known issues


Control group v2 incompatibility

Control group v2 (cgroup v2) is incompatible with Anthos clusters on bare metal 1.6. Kubernetes 1.18 does not support cgroup v2. Also Docker only offers experimental support as of 20.10. systemd switched to cgroup v2 by default in version 247.2-2. The presence of /sys/fs/cgroup/cgroup.controllers indicates that your system uses cgroup v2.

Starting with Anthos clusters on bare metal 1.6.2, the preflight checks verify that cgroup v2 is not in use on the cluster machine.

Benign error messages during installation

During highly available (HA) cluster installation, you may see errors about etcdserver leader change. These error messages are benign and can be ignored.

When you use bmctl for cluster installation, you may see a Log streamer failed to get BareMetalMachine log message at the very end of the create-cluster.log. This error message is benign and can be ignored.

When examining cluster creation logs, you may notice transient failures about registering clusters or calling webhooks. These errors can be safely ignored, because the installation will retry these operations until they succeed.

Preflight checks and service account credentials

For installations triggered by admin or hybrid clusters (in other words, clusters not created with bmctl, like user clusters), the preflight check does not verify Google Cloud Platform service account credentials or their associated permissions.

Application default credentials and bmctl

bmctl uses Application Default Credentials (ADC) to validate the cluster operation's location value in the cluster spec when it is not set to global.

For ADC to work, you need to either point the GOOGLE_APPLICATION_CREDENTIALS environment variable to a service account credential file, or run gcloud auth application-default login.

Docker service

On cluster node machines, if the Docker executable is present in the PATH environment variable, but the Docker service is not active, preflight check will fail and report that the Docker service is not active. To fix this error, either remove Docker, or enable the Docker service.

Upgrading Anthos clusters on bare metal

Upgrading is not available in the 1.6.0 release.


User cluster credentials

The bmctl reset command relies on the top-level credentials section in the cluster configuration file. For user clusters, you will need to manually update the file to add the credentials section.

Mount points and fstab

Reset does not unmount the mount points under /mnt/anthos-system and /mnt/localpv-share/. It also does not clean up the corresponding entries in /etc/fstab.

Namespace deletion

Deleting a namespace will prevent new resources from being created in that namespace, including jobs to reset machines. When deleting a user cluster, you must delete the cluster object first before deleting its namespace. Otherwise, the jobs to reset machines cannot get created, and the deletion process will skip the machine clean-up step.


The cluster CA/certificate will be rotated during upgrade. On-demand rotation support is not currently available.

Anthos clusters on bare metal rotates kubelet serving certificates automatically. Each kubelet node agent can send out a Certificate Signing Request (CSR) when a certificate nears expiration. A controller in your admin clusters validates and approves the CSR.


Pod connectivity failures and reverse path filtering

Anthos clusters on bare metal configures reverse path filtering on nodes to disable source validation (net.ipv4.conf.all.rp_filter=0). If therp_filter setting is changed to 1 or 2, pods will fail due to out-of-node communication timeouts.

Reverse path filtering is set with rp_filter files in the IPv4 configuration folder (net/ipv4/conf/all). This value may also be overridden by sysctl, which stores reverse path filtering settings in a network security configuration file, such as /etc/sysctl.d/60-gce-network-security.conf.

To restore Pod connectivity, either set net.ipv4.conf.all.rp_filter back to 0 manually, or restart the anetd Pod to set net.ipv4.conf.all.rp_filter back to 0. To restart the anetd Pod, use the following commands to locate and delete the anetd Pod and a new anetd Pod will start up in its place:

kubectl get pods -n kube-system
kubectl delete pods -n kube-system ANETD_XYZ

Replace ANETD_XYZ with the name of the anetd Pod.

Bootstrap (kind) cluster IP addresses and cluster node IP addresses overlapping and are the default pod and service CIDRs used by the bootstrap (kind) cluster. Preflight checks will fail if they overlap with cluster node machine IP addresses. To avoid the conflict, you can pass the --bootstrap-cluster-pod-cidr and --bootstrap-cluster-service-cidr flags to bmctl to specify different values.

Overlapping IP addresses across different clusters

There is no preflight check to validate overlapping IP addresses across different clusters.

hostport feature in Anthos clusters on bare metal

The hostport feature in ContainerPort is not currently supported.

Operating system endpoint limitations

On RHEL and CentOS, there is a cluster level limitation of 100,000 endpoints. This number is the sum of all pods that are referenced by a Kubernetes service. If 2 services reference the same set of pods, this counts as 2 separate sets of endpoints. The underlying nftable implementation on RHEL and CentOS causes this limitation; it is not an intrinsic limitation of Anthos clusters on bare metal.


Control plane and load balancer specifications

The control plane and load balancer node pool specifications are special. These specifications declare and control critical cluster resources. The canonical source for these resources is their respective sections in the cluster config file:

  • spec.controlPlane.nodePoolSpec
  • spec.LoadBalancer.nodePoolSpec

Consequently, do not modify the top-level control plane and load balancer node pool resources directly. Modify the associated sections in the cluster config file instead.

Mutable fields in the cluster and node pool specification

Currently, only the following cluster and node pool specification fields in the cluster config file can be updated after the cluster is created (they are mutable fields):

  • For the Cluster object (kind: Cluster), the following fields are mutable:

    • spec.anthosBareMetalVersion
    • spec.bypassPreflightCheck
    • spec.controlPlane.nodePoolSpec.nodes
    • spec.loadBalancer.nodePoolSpec.nodes
    • spec.maintenanceBlocks
    • spec.nodeAccess.loginUser
  • For the NodePool object (kind: NodePool), the following fields are mutable:

    • spec.nodes

Node shows NotReady status

Under certain load conditions, Anthos clusters on bare metal 1.6.x nodes may display a NotReady status due to Pod Lifecycle Event Generator (PLEG) being unhealthy. The node status will contain the following entry:

PLEG is not healthy: pleg was last seen active XXXmXXXs ago; threshold is 3m0s

How do I know if I'm affected?

A likely cause of this issue is the runc binary version. To confirm if you have the problematic version installed, connect to one of the cluster machines using SSH and run:

/usr/bin/runc -v

If the output is 1.0.0-rc93, then you have the problematic version installed.

Possible workarounds

To resolve this issue, we recommend upgrading to Anthos clusters on bare metal 1.7.0 or a later version.

If upgrading is not an option, you can revert the package to an earlier version on the problematic node machines. To do this, connect to the node machine using SSH and run:


apt install


dnf install