Replication

The Container Storage Modules Operator installs the Replication module for supported Dell CSI Drivers, deploying the Replication sidecar and Controller Manage.

Prerequisites

To configure Replication prior to installation via Container Storage Modules Operator, you need:

• a source cluster, which is the main cluster

• a target cluster, which will serve as the disaster recovery cluster

  NOTE: If using a single Kubernetes cluster in a stretched configuration, there will be only one cluster. The source cluster is also the target cluster.

• (Optional) If Container Storage Modules Replication is being deployed using two clusters in an environment where the DNS is not configured, and the cluster API endpoints are FQDNs, it is necessary to add the <FQDN>:<IP> mapping in the /etc/hosts file in order to resolve queries to the remote API server. This change will need to be made to the /etc/hosts file on:

  • The bastion node(s) (or wherever repctl is used).
  • Either the Container Storage Modules Operator Deployment or ClusterServiceVersion custom resource if using an Operator Lifecycle Manager (such as with an OperatorHub install).
  • Both dell-replication-controller-manager deployments covered in Configuration Steps below.

  Update the ClusterServiceVersion before continuing. Execute the command below, replacing the fields for the remote cluster’s FQDN and IP.

     kubectl patch clusterserviceversions.operators.coreos.com -n <operator-namespace> dell-csm-operator-certified.v1.3.0 \
     --type=json -p='[{"op": "add", "path": "/spec/install/spec/deployments/0/spec/template/spec/hostAliases", "value": [{"ip":"<remote-IP>","hostnames":["<remote-FQDN>"]}]}]'
  

Cloning the GitHub Repository and Building repctl

The csm-replication GitHub repository is cloned to your source cluster as part of the installation. On your source cluster run the following to clone and build the repctl tool:

git clone -b v1.12.0 https://github.com/dell/csm-replication.git
cd csm-replication/repctl
make build

Alternately, you can download a pre-built repctl binary from our Releases page.

wget https://github.com/dell/csm-replication/releases/download/v1.12.0/repctl-linux-amd64
mv repctl-linux-amd64 repctl
chmod +x repctl

The rest of the instructions will assume that your current working directory is the csm-replication/repctl directory.

Configuration Steps

To configure Replication perform the following steps:

1. Collect the cluster admin configurations for each of the clusters. In the following example the source cluster, cluster-1 uses configuration /root/.kube/config-1 and the target cluster, cluster-2 uses the configuration /root/.config/config-2. Use repctl to add the clusters:

   ./repctl cluster add -f "/root/.kube/config-1","/root/.kube/config-2" -n "cluster-1","cluster-2"
   

   NOTE: If using a single Kubernetes cluster in a stretched configuration there will be only one cluster. Adding this cluster to repctl and performing the service account configuration injection in step 3 are still mandatory.

2. Inject the service account’s configuration into the clusters.

   ./repctl cluster inject
   

   NOTE: To inject the service account’s configuration for each cluster individually, use the following command:

   ./repctl cluster inject --custom-configs $HOME/.repctl/clusters/<config-name>
   

   Example:

    ./repctl cluster inject --custom-configs "/root/.repctl/clusters/config-1"
   

3. Customize the examples/<storage>_example_values.yaml sample config. Set the values for sourceClusterID and targetClusterID to the same names used in step 1. For a stretched cluster set both fields to self.

4. Create the replication storage classes using the modified configuration from step 3:

   ./repctl create sc --from-config ./examples/<storage>_example_values.yaml
   

5. On both source and target clusters, configure any driver-specific prerequisites for deploying the driver via Dell CSM Operator.

6. Install the CSI driver for your chosen storage platform on the source cluster according to the instructions for installing the drivers using CSM Operator. Ensure that replication is set to enabled in the custom resource YAML used to install the driver, under the components field.

   NOTE: As of CSM release 1.14, all Custom Resource Definitions that are required for Replication functionality are installed by the CSM Operator automatically when a Replication-enabled driver is installed.

7. Repeat the installation of the CSI driver for your chosen storage platform on the target cluster. Again, ensure that replication is set to enabled in the custom resource YAML used for installation, under the components field. This is not necessary in stretched-cluster configurations that do not have a separate target cluster.

8. (Optional) If CSM Replication is deployed using two clusters in an environment where the DNS is not configured, it is necessary to update the dell-replication-controller-manager Kubernetes deployment to map the API endpoint FQDN to an IP address by adding the hostAliases field and associated FQDN:IP mappings.

   To update the dell-replication-controller-manager deployment, execute the command below, replacing the fields for the remote cluster’s FQDN and IP. Make sure to update the deployment on both the primary and disaster recovery clusters.

   kubectl patch deployment -n dell-replication-controller dell-replication-controller-manager \
   -p '{"spec":{"template":{"spec":{"hostAliases":[{"hostnames":["<remote-FQDN>"],"ip":"<remote-IP>"}]}}}}'