Backing up and restoring

You can backup and restore your Event Processing flows and Flink instances as follows.

Event Processing flows

You can export your existing Event Processing flows to save them, making them available to import later, as described in exporting flows.

Flink instances

A Flink savepoint is a consistent image of a Flink job’s execution state. Backing up your Flink instances involves backing up savepoints. This document is intended for Flink jobs running in an application mode Flink cluster.

Prerequisites

This procedure assumes that you have the following deployed:

An instance of Flink deployed by the IBM Operator for Apache Flink and configured with persistent storage with a PersistentVolumeClaim (PVC).
Flink jobs as application deployments.

The FlinkDeployment custom resource that configures your Flink instance must define the hereafter parameters, each pointing to a different directory on the persistent storage.

spec.flinkConfiguration.state.checkpoints.dir
spec.flinkConfiguration.state.savepoints.dir
spec.flinkConfiguration.high-availability.storageDir (if high availability is required)

Note: These directories are automatically created by Flink if they do not exist.

Backing up

The backup process captures the latest state of a running Flink job and its specification, allowing to re-create the job from the saved state when required. To back up your Flink instance, update each of your deployed instances by editing their respective FlinkDeployment custom resources as follows:

Ensure that the status section indicates that a JobManager is ready and the Flink job is running by checking the FlinkDeployment custom resource.
```
status:
  jobManagerDeploymentStatus: READY
  jobStatus:
    state: RUNNING
```
Edit the FlinkDeployment custom resource and make the following changes:

a. Set the value of spec.job.upgradeMode to savepoint.

b. Set the value of spec.job.state to running.

c. Set the value of spec.job.savepointTriggerNonce to an integer that has never been used before for that option.

For example:
```
job:
   jarURI: local:///opt/flink/usrlib/sql-runner.jar
   args: ["/opt/flink/usrlib/sql-scripts/statements.sql"]
   savepointTriggerNonce: <integer value>
   state: running
   upgradeMode: savepoint
```
Save a copy of the FlinkDeployment custom resource.
Keep the FlinkDeployment custom resource and the PVC bound to a persistent volume (PV) containing the savepoint to make them available later for restoring your deployment.

Restoring

To restore a previously backed-up Flink instance, ensure that the PVC bound to a persistent volume (PV) containing the snapshot is available, then update your FlinkDeployment custom resource as follows.

Create a new PVC pointing to the PV containing the snapshot.
Edit the saved FlinkDeployment custom resource that you saved when backing up your instance:

a. Set the value of spec.job.upgradeMode to savepoint.

b. Set the value of spec.job.state to running to resume the Flink job.

c. Ensure that the same directory is set for the parameters spec.job.initialSavepointPath and spec.flinkConfiguration["state.savepoints.dir"].

For example:
```
job:
   jarURI: local:///opt/flink/usrlib/sql-runner.jar
   args: ["/opt/flink/usrlib/sql-scripts/statements.sql"]
   state: running
   upgradeMode: savepoint
   initialSavepointPath: <savepoint directory>
   allowNonRestoredState: true
```
Apply the modified FlinkDeployment custom resource.