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External Storage Cluster

An external cluster is a Ceph configuration that is managed outside of the local K8s cluster. The external cluster could be managed by cephadm, or it could be another Rook cluster that is configured to allow the access (usually configured with host networking).

In external mode, Rook will provide the configuration for the CSI driver and other basic resources that allows your applications to connect to Ceph in the external cluster.

External configuration

  • Source cluster: The cluster providing the data, usually configured by cephadm

  • Consumer cluster: The K8s cluster that will be consuming the external source cluster


Create the desired types of storage in the provider Ceph cluster:

Commands on the source Ceph cluster

In order to configure an external Ceph cluster with Rook, we need to extract some information in order to connect to that cluster.

1. Create all users and keys

Run the python script for creating all users and keys.

python3 --rbd-data-pool-name <pool_name> --cephfs-filesystem-name <filesystem-name> --rgw-endpoint  <rgw-endpoint> --namespace <namespace> --format bash
  • --namespace: Namespace where CephCluster will run, for example rook-ceph
  • --format bash: The format of the output
  • --rbd-data-pool-name: The name of the RBD data pool
  • --alias-rbd-data-pool-name: Provides an alias for the RBD data pool name, necessary if a special character is present in the pool name such as a period or underscore
  • --rgw-endpoint: (optional) The RADOS Gateway endpoint in the format <IP>:<PORT> or <FQDN>:<PORT>.
  • --rgw-pool-prefix: (optional) The prefix of the RGW pools. If not specified, the default prefix is default
  • --rgw-tls-cert-path: (optional) RADOS Gateway endpoint TLS certificate file path
  • --rgw-skip-tls: (optional) Ignore TLS certification validation when a self-signed certificate is provided (NOT RECOMMENDED)
  • --rbd-metadata-ec-pool-name: (optional) Provides the name of erasure coded RBD metadata pool, used for creating ECRBDStorageClass.
  • --monitoring-endpoint: (optional) Ceph Manager prometheus exporter endpoints (comma separated list of IP entries of active and standby mgrs)
  • --monitoring-endpoint-port: (optional) Ceph Manager prometheus exporter port
  • --skip-monitoring-endpoint: (optional) Skip prometheus exporter endpoints, even if they are available. Useful if the prometheus module is not enabled
  • --ceph-conf: (optional) Provide a Ceph conf file
  • --keyring: (optional) Path to Ceph keyring file, to be used with --ceph-conf
  • --k8s-cluster-name: (optional) Kubernetes cluster name
  • --output: (optional) Output will be stored into the provided file
  • --dry-run: (optional) Prints the executed commands without running them
  • --run-as-user: (optional) Provides a user name to check the cluster's health status, must be prefixed by client.
  • --cephfs-metadata-pool-name: (optional) Provides the name of the cephfs metadata pool
  • --cephfs-filesystem-name: (optional) The name of the filesystem, used for creating CephFS StorageClass
  • --cephfs-data-pool-name: (optional) Provides the name of the CephFS data pool, used for creating CephFS StorageClass
  • --rados-namespace: (optional) Divides a pool into separate logical namespaces, used for creating RBD PVC in a CephBlockPoolRadosNamespace (should be lower case)
  • --subvolume-group: (optional) Provides the name of the subvolume group, used for creating CephFS PVC in a subvolumeGroup
  • --rgw-realm-name: (optional) Provides the name of the rgw-realm
  • --rgw-zone-name: (optional) Provides the name of the rgw-zone
  • --rgw-zonegroup-name: (optional) Provides the name of the rgw-zone-group
  • --upgrade: (optional) Upgrades the cephCSIKeyrings(For example: client.csi-cephfs-provisioner) and client.healthchecker ceph users with new permissions needed for the new cluster version and older permission will still be applied.
  • --restricted-auth-permission: (optional) Restrict cephCSIKeyrings auth permissions to specific pools, and cluster. Mandatory flags that need to be set are --rbd-data-pool-name, and --k8s-cluster-name. --cephfs-filesystem-name flag can also be passed in case of CephFS user restriction, so it can restrict users to particular CephFS filesystem.
  • --v2-port-enable: (optional) Enables the v2 mon port (3300) for mons.
  • --topology-pools: (optional) Comma-separated list of topology-constrained rbd pools
  • --topology-failure-domain-label: (optional) K8s cluster failure domain label (example: zone, rack, or host) for the topology-pools that match the ceph domain
  • --topology-failure-domain-values: (optional) Comma-separated list of the k8s cluster failure domain values corresponding to each of the pools in the topology-pools list


To enable multi-tenancy, run the script with the --restricted-auth-permission flag and pass the mandatory flags with it, It will generate the secrets which you can use for creating new Consumer cluster deployment using the same Source cluster(ceph cluster). So you would be running different isolated consumer clusters on top of single Source cluster.


Restricting the csi-users per pool, and per cluster will require creating new csi-users and new secrets for that csi-users. So apply these secrets only to new Consumer cluster deployment while using the same Source cluster.

python3 --cephfs-filesystem-name <filesystem-name> --rbd-data-pool-name <pool_name> --k8s-cluster-name <k8s-cluster-name> --restricted-auth-permission true --format <bash> --rgw-endpoint <rgw_endpoint> --namespace <rook-ceph>

RGW Multisite

Pass the --rgw-realm-name, --rgw-zonegroup-name and --rgw-zone-name flags to create the admin ops user in a master zone, zonegroup and realm. See the Multisite doc for creating a zone, zonegroup and realm.

python3 --rbd-data-pool-name <pool_name> --format bash --rgw-endpoint <rgw_endpoint> --rgw-realm-name <rgw_realm_name>> --rgw-zonegroup-name <rgw_zonegroup_name> --rgw-zone-name <rgw_zone_name>>

Topology Based Provisioning

Enable Topology Based Provisioning for RBD pools by passing --topology-pools, --topology-failure-domain-label and --topology-failure-domain-values flags. A new storageclass named ceph-rbd-topology will be created by the import script with volumeBindingMode: WaitForFirstConsumer. The storageclass is used to create a volume in the pool matching the topology where a pod is scheduled.

For more details, see the Topology-Based Provisioning

Upgrade Example

  1. If consumer cluster doesn't have restricted caps, this will upgrade all the default csi-users (non-restricted):

    python3 --upgrade
  2. If the consumer cluster has restricted caps: Restricted users created using --restricted-auth-permission flag need to pass mandatory flags: '--rbd-data-pool-name(if it is a rbd user), --k8s-cluster-name and --run-as-user' flags while upgrading, in case of cephfs users if you have passed --cephfs-filesystem-name flag while creating csi-users then while upgrading it will be mandatory too. In this example the user would be client.csi-rbd-node-rookstorage-replicapool (following the pattern csi-user-clusterName-poolName)

    python3 --upgrade --rbd-data-pool-name replicapool --k8s-cluster-name rookstorage --run-as-user client.csi-rbd-node-rookstorage-replicapool


An existing non-restricted user cannot be converted to a restricted user by upgrading. The upgrade flag should only be used to append new permissions to users. It shouldn't be used for changing a csi user already applied permissions. For example, you shouldn't change the pool(s) a user has access to.

Admin privileges

If in case the cluster needs the admin keyring to configure, update the admin key rook-ceph-mon secret with client.admin keyring


Sharing the admin key with the external cluster is not generally recommended

  1. Get the client.admin keyring from the ceph cluster

    ceph auth get client.admin
  2. Update two values in the rook-ceph-mon secret:

    • ceph-username: Set to client.admin
    • ceph-secret: Set the client.admin keyring

After restarting the rook operator (and the toolbox if in use), rook will configure ceph with admin privileges.

2. Copy the bash output

Example Output:

export ROOK_EXTERNAL_FSID=797f411a-aafe-11ec-a254-fa163e1539f5
export ROOK_EXTERNAL_USERNAME=client.healthchecker
export ROOK_EXTERNAL_CEPH_MON_DATA=ceph-rados-upstream-w4pdvq-node1-installer=
export RBD_POOL_NAME=replicated_2g
export RGW_POOL_PREFIX=default

Commands on the K8s consumer cluster

Helm Installation

To install with Helm, the rook cluster helm chart will configure the necessary resources for the external cluster with the example values-external.yaml.

cd deploy/examples/charts/rook-ceph-cluster
helm repo add rook-release
helm install --create-namespace --namespace $clusterNamespace rook-ceph rook-release/rook-ceph -f values.yaml
helm install --create-namespace --namespace $clusterNamespace rook-ceph-cluster \
--set operatorNamespace=$operatorNamespace rook-release/rook-ceph-cluster -f values-external.yaml

Skip the manifest installation section and continue with Cluster Verification.

Manifest Installation

If not installing with Helm, here are the steps to install with manifests.

  1. Deploy Rook, create common.yaml, crds.yaml and operator.yaml manifests.

  2. Create common-external.yaml and cluster-external.yaml

Import the Source Data

  1. Paste the above output from into your current shell to allow importing the source data.

  2. The import script in the next step uses the current kubeconfig context by default. If you want to specify the kubernetes cluster to use without changing the current context, you can specify the cluster name by setting the KUBECONTEXT environment variable.

    export KUBECONTEXT=<cluster-name>
  3. Here is the link for import script. The script has used the rook-ceph namespace and few parameters that also have referenced from namespace variable. If user's external cluster has a different namespace, change the namespace parameter in the script according to their external cluster. For example with new-namespace namespace, this change is needed on the namespace parameter in the script.

  4. Run the import script.


    If your Rook cluster nodes are running a kernel earlier than or equivalent to 5.4, remove fast-diff, object-map, deep-flatten,exclusive-lock from the imageFeatures line.


Cluster Verification

  1. Verify the consumer cluster is connected to the source ceph cluster:

    $ kubectl -n rook-ceph  get CephCluster
    rook-ceph-external   /var/lib/rook                162m   Connected   HEALTH_OK
  2. Verify the creation of the storage class depending on the rbd pools and filesystem provided. ceph-rbd and cephfs would be the respective names for the RBD and CephFS storage classes.

    kubectl -n rook-ceph get sc
  3. Then you can now create a persistent volume based on these StorageClass.

Connect to an External Object Store

Create the external object store CR to configure connection to external gateways.

cd deploy/examples/external
kubectl create -f object-external.yaml

Consume the S3 Storage, in two different ways:

  1. Create an Object store user for credentials to access the S3 endpoint.

    cd deploy/examples
    kubectl create -f object-user.yaml
  2. Create a bucket storage class where a client can request creating buckets and then create the Object Bucket Claim, which will create an individual bucket for reading and writing objects.

    cd deploy/examples/external
    kubectl create -f storageclass-bucket-delete.yaml
    kubectl create -f object-bucket-claim-delete.yaml


For more details see the Object Store topic

Connect to v2 mon port

If encryption or compression on the wire is needed, specify the --v2-port-enable flag. If the v2 address type is present in the ceph quorum_status, then the output of 'ceph mon data' i.e, ROOK_EXTERNAL_CEPH_MON_DATA will use the v2 port(3300).

NFS storage

Rook suggests a different mechanism for making use of an NFS service running on the external Ceph standalone cluster, if desired.

Exporting Rook to another cluster

If you have multiple K8s clusters running, and want to use the local rook-ceph cluster as the central storage, you can export the settings from this cluster with the following steps.

  1. Copy into the directory /etc/ceph/ of the toolbox.

    toolbox=$(kubectl get pod -l app=rook-ceph-tools -n rook-ceph -o jsonpath='{.items[*]}')
    kubectl -n rook-ceph cp deploy/examples/external/ $toolbox:/etc/ceph
  2. Exec to the toolbox pod and execute with needed options to create required users and keys.


For other clusters to connect to storage in this cluster, Rook must be configured with a networking configuration that is accessible from other clusters. Most commonly this is done by enabling host networking in the CephCluster CR so the Ceph daemons will be addressable by their host IPs.