ApplicationRegistration in AKS

With Stork, you can back up and restore customer-specific CRDs. Using this method, you create a Stork custom resource, called an ApplicationRegistration, which registers your CRD with Stork, allowing you to perform a migration, backup, and restore of your CRDs specified resources.

Prerequisites

• Your Portworx installation must contain the libopenstorage/stork:2.4.3 image.

Fetch default ApplicationRegistrations

By default, Stork supports a number of customer-specific CRDs. List the existing defaults by entering the storkctl get appreg command:

storkctl get applicationregistrations

NAME        KIND                       CRD-NAME                 VERSION    SUSPEND-OPTIONS                       KEEP-STATUS
cassandra   CassandraDatacenter        cassandra.datastax.com   v1beta1    spec.stopped,bool                     false
couchbase   CouchbaseBucket            couchbase.com            v2                                               false
couchbase   CouchbaseCluster           couchbase.com            v2         spec.paused,bool                      false
couchbase   CouchbaseEphemeralBucket   couchbase.com            v2                                               false
couchbase   CouchbaseMemcachedBucket   couchbase.com            v2                                               false
couchbase   CouchbaseReplication       couchbase.com            v2                                               false
couchbase   CouchbaseUser              couchbase.com            v2                                               false
couchbase   CouchbaseGroup             couchbase.com            v2                                               false
couchbase   CouchbaseRoleBinding       couchbase.com            v2                                               false
couchbase   CouchbaseBackup            couchbase.com            v2                                               false
couchbase   CouchbaseBackupRestore     couchbase.com            v2                                               false
ibm         IBPCA                      ibp.com                  v1alpha1   spec.replicas,int                     false
ibm         IBPConsole                 ibp.com                  v1alpha1   spec.replicas,int                     false
ibm         IBPOrderer                 ibp.com                  v1alpha1   spec.replicas,int                     false
ibm         IBPPeer                    ibp.com                  v1alpha1   spec.replicas,int                     false
redis       RedisEnterpriseCluster     app.redislabs.com        v1                                               false
redis       RedisEnterpriseDatabase    app.redislabs.com        v1                                               false
weblogic    Domain                     weblogic.oracle          v8         spec.serverStartPolicy,string,NEVER   false

Register a new CRD with Stork

To register a new CRD with Stork, perform the following steps:

1. Create an applicationregistration spec, specifying the following:

• metadata.name: With the name of the spec.

• resources.PodsPath: (Optional) With The path which stores the pods created by the CR. These will be deleted when scaling down the migration.

• resources.group: With the group of the CRD being registered.

• resources.version: With the version of the CRD being registered.

• resources.kind: With the kind of the CRD being registered.

• resources.keepStatus: (Optional) If you don't want to save the resource's status after migration, set this value to false.

• resources.suspendOptions.path: (Optional) With the path in the CRD spec which contains the option to suspend the application.

• resources.suspendOptions.type: (Optional) With the type of the field that is used to suspend the operation. For example, int, if the field contains the replica count for the application.

  apiVersion: stork.libopenstorage.org/v1alpha1
  kind: ApplicationRegistration
  metadata:
    name: myappname
  resources:
  - PodsPath: <POD_PATH> 
    group: <CRD_GROUP_NAME>
    version: <CRD_VERSION>
    kind: <CR_KIND>
    # to keep status of CR on migration <!-- where does this apply? to keepStatus below it? can you elaborate more on the statement? -->
    keepStatus: false
    # To disable CR on migration, 
    # CR spec path for disable 
    suspendOptions:
      path: <spec_path>
      type: <type_of_value_to_set> (can be "int"/"bool")

  The following example ApplicationRegistration allows Stork to back-up, restore, or migrate a datastax/cassandra operator:

  apiVersion: stork.libopenstorage.org/v1alpha1
  kind: ApplicationRegistration
  metadata:
    name: cassandra
  resources:
  - PodsPath: ""
    group: cassandra.datastax.com
    version: v1beta1
    kind: CassandraDatacenter
    keepStatus: false #cassandra datacenter status will not be migrated
    suspendOptions:
      path: spec.stopped #path to disable cassandra datacenter
      type: bool #type of value to be set for spec.stopped

2. Apply the spec:

kubectl apply -f <application-registration-spec>.yaml

Once you've applied the spec, you can verify it by entering the following storkctl get command, specifying your own application name:

storkctl get appreg <app-name>

NAME        KIND                  CRD-NAME                 VERSION   SUSPEND-OPTIONS     KEEP-STATUS
cassandra   CassandraDatacenter   cassandra.datastax.com   v1beta1   spec.stopped,bool   false

note

If you register your CRD with Stork using an applicationRegistration CRD, you do not need to modify the migration, backup, or restore specs.

Managing application migrations with Stork

Migration of applications controlled by operators in Stork can be conducted with either asynchronous or synchronous DR methods. When the startApplications parameter is set to false for migrations, it is expected that the application pods will not be running in the destination cluster once the migration is completed. For DR scenarios, the startApplications flag is by default set to false since the applications need to be in a scale down state on the destination cluster.

Different applications may require specific scaling down procedures by modifying certain parameters in their Custom Resource (CR) specifications. Stork provides support for modifying the CR spec to scale down these applications, utilizing the options provided by the ApplicationRegistration's suspendOptions. See here for the list of options.

Safeguarding application pods during migration with Stork's stash strategy

For certain applications controlled by clusterwide operators that do not support scaling down via CR spec modifications, the pods related to these applications may become active in the destination namespace after migration. This can be problematic if the intention is to avoid starting the application in the destination cluster before performing the actual failover.

To prevent the application pods from becoming active prematurely, Stork offers a feature known as the "Stash Strategy". This feature allows the CR content to be stashed in a config map during migration on the destination cluster. The actual CR spec is created on the destination cluster only when the applications failover to the destination cluster using storkctl.

note

The stashStrategy feature is only available starting from Stork version 23.8.0. Moreover, do not define any suspend options for application registrations with the stashStrategy enabled.

Here is an example of an application registration for Elasticsearch with the stash strategy enabled. Modifications need to be made in both the source and destination clusters before initiating the migration:

apiVersion: stork.libopenstorage.org/v1alpha1
kind: ApplicationRegistration
metadata:
  name: elasticsearch
resources:
- group: elasticsearch.k8s.elastic.co
  keepStatus: false
  kind: Elasticsearch
  stashStrategy:
    stashCR: true
  version: v1
- group: elasticsearch.k8s.elastic.co
  keepStatus: false
  kind: Elasticsearch
  stashStrategy:
    stashCR: true
  version: v1beta1
- group: elasticsearch.k8s.elastic.co
  keepStatus: false
  kind: Elasticsearch
  stashStrategy:
    stashCR: true
  version: v1alpha1