Anthos clusters on bare metal is now Google Distributed Cloud (software only) for bare metal. For more information, see the product overview.

Create hybrid clusters

In Google Distributed Cloud, hybrid clusters perform the dual role of an admin cluster and a user cluster. They run workloads, and at the same time, manage other clusters, and themselves.

Hybrid clusters eliminate the need to run a separate admin cluster in resource-constrained scenarios, and can provide highly available (HA) reliability. In an HA hybrid cluster, if one node fails, then others will take its place.

Hybrid clusters are different from standalone clusters in that they can also manage other clusters. Standalone clusters can't create or manage other clusters.

When you create hybrid clusters, there is some tradeoff between flexibility and security, however. Since hybrid clusters manage themselves, running workloads on the same cluster increases the risk of security exposure to sensitive administrative data, like SSH keys.

You create a hybrid cluster with a high availability (HA) control plane using the bmctl command. The bmctl command can be run on a separate workstation or on one of the hybrid cluster nodes.

Prerequisites

Latest bmctl is downloaded (gs://anthos-baremetal-release/bmctl/1.30.200-gke.101/linux-amd64/bmctl) from Cloud Storage.
Workstation running bmctl has network connectivity to all nodes in the target hybrid cluster.
Workstation running bmctl has network connectivity to the control plane VIP of the target hybrid cluster.
SSH key used to create the hybrid cluster is available to root, or there is SUDO user access on all nodes in the target hybrid cluster.
Connect-register service account is configured for use with Connect.

See the Google Distributed Cloud quickstart for expanded step-by-step instructions for creating a hybrid cluster.

Enable SELinux

If you want to enable SELinux to secure your containers, you must make sure that SELinux is enabled in Enforced mode on all your host machines. Starting with Google Distributed Cloud release 1.9.0 or later, you can enable or disable SELinux before or after cluster creation or cluster upgrades. SELinux is enabled by default on Red Hat Enterprise Linux (RHEL). If SELinux is disabled on your host machines or you aren't sure, see Securing your containers using SELinux for instructions on how to enable it.

Google Distributed Cloud supports SELinux in only RHEL systems.

Log into gcloud and create a cluster configuration file

Log into the gcloud CLI as a user using gcloud auth application-default login:
```
gcloud auth application-default login
```
You need to have a Project Owner or Editor role to use the automatic API enablement and Service Account creation features, described in the following sections.

You can also add the following IAM roles to the user:
- Service Account Admin
- Service Account Key Admin
- Project IAM Admin
- Compute Viewer
- Service Usage Admin
Alternatively, if you already have a service account with those roles, run:
```
export GOOGLE_APPLICATION_CREDENTIALS=JSON_KEY_FILE
```
Replace JSON_KEY_FILE with the path of your service account JSON key file.
Get your Google Cloud project ID to use with cluster creation:
```
export CLOUD_PROJECT_ID=$(gcloud config get-value project)
```

Create the cluster configuration file with `bmctl`

After you've logged into the gcloud CLI and have your project set up, you can create the cluster configuration file with the bmctl command.

To create a cluster configuration file:

Run the following command creates the cluster configuration file, creates all needed service accounts, and enables all required APIs:
```
bmctl create config -c CLUSTER_NAME</var> --enable-apis \
    --create-service-accounts --project-id=CLOUD_PROJECT_ID
```
Replace the following:
- CLUSTER_NAME: the name of the cluster you're creating.
- CLOUD_PROJECT_ID: the ID of your Google Cloud project.
By default, the configuration file is written to bmctl-workspace/CLUSTER_NAME/CLUSTER_NAME.yaml.

If you've already enabled APIs and created service accounts, you can create configuration files without enabling APIs and creating service accounts. You also aren't required to use the --project-id flag. However, you'll need to specify credentials in your configuration file manually.

For more information about command options, see create config.

Edit the cluster configuration file

Now that you have a cluster configuration file, edit it to make the following changes:

Provide the SSH private key to access the hybrid cluster nodes:

# bmctl configuration variables. Because this section is valid YAML but not a valid Kubernetes
# resource, this section can only be included when using bmctl to
# create the initial admin/hybrid cluster. Afterwards, when creating user clusters by directly
# applying the cluster and node pool resources to the existing cluster, you must remove this
# section.
gcrKeyPath: bmctl-workspace/.sa-keys/my-gcp-project-anthos-baremetal-gcr.json
sshPrivateKeyPath: /path/to/your/ssh_private_key
gkeConnectAgentServiceAccountKeyPath: bmctl-workspace/.sa-keys/my-gcp-project-anthos-baremetal-connect.json
gkeConnectRegisterServiceAccountKeyPath: bmctl-workspace/.sa-keys/my-gcp-project-anthos-baremetal-register.json
cloudOperationsServiceAccountKeyPath: bmctl-workspace/.sa-keys/my-gcp-project-anthos-baremetal-cloud-ops.json

Register your clusters to a fleet. The project ID that you specified in the bmctl create config command is automatically added to the gkeConnect.projectID field in the cluster configuration file. This project is referred to as the fleet host project.
- If you created your configuration file, using the automatic API enablement and Service Account creation features, you can skip this step.
- If you created the configuration file without using the automatic API enablement and Service Account creation features, reference the downloaded service account JSON keys in the corresponding gkeConnectAgentServiceAccountKeyPath and gkeConnectRegisterServiceAccountKeyPath fields of the cluster configuration file.

Change the config to specify a cluster type of hybrid instead of admin:

spec:
  # Cluster type. This can be:
  #   1) admin:  to create an admin cluster. This can later be used to create user clusters.
  #   2) user:   to create a user cluster. Requires an existing admin cluster.
  #   3) hybrid: to create a hybrid cluster that runs admin cluster components and user workloads.
  #   4) standalone: to create a cluster that manages itself, runs user workloads, but does not manage other clusters.
  type: hybrid

Change the config to specify a multi-node, high availability control plane. You want to specify an odd number of nodes to be able to have a majority quorum for HA:
```
  # Control plane configuration
  controlPlane:
    nodePoolSpec:
      nodes:
      # Control plane node pools. Typically, this is either a single machine
      # or 3 machines if using a high availability deployment.
      - address: 10.200.0.4
      - address: 10.200.0.5
      - address: 10.200.0.6
```
Note: If you have an even number of nodes temporarily while adding or removing nodes for maintenance or replacement, your deployment maintains HA as long as you have enough quorum.
Specify the pod density of cluster nodes:
```
....
# NodeConfig specifies the configuration that applies to all nodes in the cluster.
nodeConfig:
  # podDensity specifies the pod density configuration.
  podDensity:
    # maxPodsPerNode specifies at most how many pods can be run on a single node.
    maxPodsPerNode: 250
....
```
For hybrid clusters, allowable values for maxPodsPerNode are 32-250 for HA clusters and 64-250 for non-HA clusters. The default value for maxPodsPerNode if unspecified is 110. Once the cluster is created, this value cannot be updated.

Pod density is also limited by your cluster's available IP resources. For details, see Pod networking.

Create the hybrid cluster with the cluster configuration

Use the bmctl command to create the cluster:

bmctl create cluster -c CLUSTER_NAME

Replace CLUSTER_NAME with the name you used when you created the cluster configuration file the previous section.

The following shows an example of the command to create a cluster named hybrid1:

bmctl create cluster -c hybrid1

Sample hybrid cluster configurations

For example hybrid cluster configurations, see Hybrid clusters in the Cluster configuration samples.