Migrate a DSE Cluster to DataStax Mission Control

DataStax Mission Control is currently in Public Preview. DataStax Mission Control is not intended for production use, has not been certified for production workloads, and might contain bugs and other functional issues. There is no guarantee that DataStax Mission Control will ever become generally available. DataStax Mission Control is provided on an “AS IS” basis, without warranty or indemnity of any kind.

If you are interested in trying out DataStax Mission Control please join the Public Preview.

Migrating an existing DSE cluster to DataStax Mission Control with zero down time is trivial and allows for the management of existing clusters without moving the data to new hardware.

Prerequisities and system requirements

DataStax Mission Control Runtime must be installed prior to migration. See Services setup with DataStax Mission Control Runtime Installer.
Each node must have the same storage group rights in the DSE data directories (ownership).
- Group read-write access must be given to DSE directories or the migration cannot continue. DataStax Mission Control changes file system groups and write access during migration.
User running DataStax Mission Control mcctl commands must have access to the DSE’s data directories (running with sudo -u is an acceptable solution).
Only JDK8 is supported as the source and target platform.
Linux is the only supported platform.
Kubernetes must be installed on every DSE node before running the migration.
Only DSE server versions 6.8.26 and later are supported. Check your version with:
```
nodetool version
```

Procedure

The migration process consists of three phases; import init, import add, and import commit.

The import init phase validates the cluster and gathers the necessary configuration data to be used as the base to determine if the migration is possible. It also creates the necessary seed services, the project in which the cluster is created, and related metadata so that migrated nodes can continue communicating with the non-migrated ones, and ensuring that the cluster stays healthy during the process. Run the import init phase only once on the first DSE node.
The import add phase runs on every DSE node in the datacenter. The import add command performs the per-node migration, using the configuration fetched in the import init phase. import add supports running in parallel and takes care of serializing the migrations.
The final import commit phase requires that the import add phase be run on every node in the cluster. It creates the necessary Kubernetes configurations. It activates all the migrated nodes to DataStax Mission Control and then reconciles them to the desired state. After achieving this state, the cluster and all of its nodes should be managed using DataStax Mission Control.

As you step through these phases, here are some useful Command Line Interface (CLI) flags for reference:

--nodetool-path: Where the nodetool command is located. This assumes a complete path including the nodetool executable. cqlsh must reside in the same path.
--nodetool status: Describes status and information about nodes in a datacenter.
--cass-config-dir: Directory where cassandra.yaml is located.
--dse-config-dir: Directory where dse.yaml is located.
--cassandra-home: Directory where DSE is installed.
--username: DSE admin account name.
--password: DSE admin password.
--jmxusername: Local JMX authentication username.
--jmxpassword: Local JMX authentication password.
--kubeconfig: Path to the kubeconfig file. If not specified, the default kubeconfig file is used.
--namespace/-n: The project/namespace in which the cluster is imported/located. If not specified, the default namespace is used.

`import init` phase

The import init phase verifies that the cluster is ready to be migrated. It must be run from a node in the cluster because it connects to the running DSE node to fetch its state. JMX access credentials are required because this phase uses nodetool. After verifying the node state, the configuration from this node is used as the base to which all of the other nodes in the managed cluster must conform. Choose a node with a good configuration to use as a generic base.

It is possible to review the configuration (or a failed run), modify the setup, and rerun the import init command. Rerunning import init replaces the values previously written to the cluster.

If the cluster is using authentication and you wish to use existing superuser username/password combination for communication, then enter them using --username and --password parameters. When no credentials are given, DataStax Mission Control creates and instates its own superuser to the cluster. Likewise, if the JMX local authentication is enabled, this DataStax Mission Control migration tool requires the JMX useraccount and password.

Run the import init command:
```
mcctl import init -n dse
```

`import add` phase

import add is the process of migrating an existing DSE node to DataStax Mission Control. The DSE node must be running before continuing. You can run multiple nodes at the same with the import add command. The command sequentially runs all the migrations, migrating a single node at a time.

The import add command requires access to modify the data directories that the running DSE instance is using. Ownership and groups of directories must be unified prior to migration. When running under DataStax Mission Control, the nodes may use a user id or group id that differs from the existing deployment, thus requiring modification as part of migration.

The import add command supports (and requires) the same parameters as does the import init command if the installation is using a custom path instead of auto-detected paths.

When jmxpassword/jmxusername/username/password parameters are not available, the values used in the import init phase are reused in the import add phase . If a .deb/.rpm package installation was used, the configuration and tool paths are using the defaults provided by the package manager. In some cases these values might not match values currently in use, and might require overriding.

To aid in detection, the import add command uses the DSE_HOME environment variable. If either the cassandra-home or the DSE_HOME environment variable is set, DataStax Mission Control tries to detect cassandra.yaml, dse.yaml, and nodetool-path from its subdirectories.

Run the import add command:
```
sudo mcctl import add -n dse
```
The import add command sequentially deletes the DSE nodes and recreates them in a K8s cluster while the cluster remains up and running.
Verify by running:
```
nodetool status
```
and
```
kubectl get pods -n dse
```

Reversing operation

At this point, the operation is reversible. This may be required if certain prerequisites are not met on every node and a particular node requires certain operations. The migration has not broken the existing DSE cluster installation, but you must remove the migrated node before continuing.

Delete the pod which this node created by running:
```
kubectl delete pod/<name> -n dse
```

List and then delete all the PersistentVolumeClaim (PVC)s and PersistentVolume (PV)s that this node mounted:

kubectl get pvc -n dse
kubectl delete pvc <pvc-name> -n dse

kubectl get pv |grep "pvc-server-data"
kubectl delete pv <pv-name>

Modify the ClusterConfig
```
kubectl edit clusterconfig cluster-migrate-config -n dse
```
and set the migrated field to false instead of true.
Restart the node using the OpsCenter procedure.

`import commit` phase

Before running the import commit phase, all the nodes must first be migrated. DataStax Mission Control checks every node’s migration status, and if any node is not migrated it exits in the validation phase. Upon successful validation, the final cluster configuration is changed and applied to all the migrated nodes. This causes a rolling restart of the cluster.

Run the import commit command:
```
mcctl import commit -n dse
```
The import commit command creates the MissionControlCluster (mccluster in short) object and finalizes the migration.

Verify by running:

kubectl command
Sample result

kubectl get mccluster -n dse

NAMESPACE         NAME      AGE
dse               dsetest   73m

At the completion of these three phases the DSE cluster is fully migrated to DataStax Mission Control with zero down time.