Synchronization

• 1: Introduction
• 2: Kubernetes/OpenShift
• 2.1: Introduction
• 2.2: Configuring a LiveSynchronization
• 2.3: Recovering from a Bucket
• 2.4: Understanding logging
• 2.5: Resynchronization
• 2.6: Configuration reference
• 2.7: Components
• 2.8: Granafa setup
• 3: Zookeeper
• 3.1: Introduction
• 3.2: Configuration

1 - Introduction

Synchronization is a critical process that enables the replication of data and configurations across different platform assets. This ensures consistency, integrity and improve the platform resiliency.

Key concepts

Source and destination

Each synchronization has at least two assets:

• Source: the original location or system from which data and configurations are retrived.
• Destination: the destination location or system where data and configurations are applied or updated.

Synchronization periodicity

There are three distinct types of synchronization processes designed to meet different operational needs: Synchronization, SynchronizationPlan, and LiveSynchronization.

Synchronization

The Synchronization process is designed to run once, making it ideal for one-time data alignment tasks or initial setup processes. This type of synchronization is useful when a system or component needs to be brought up-to-date with the latest data and configurations from another source without ongoing updates.

SynchronizationPlan

The SynchronizationPlan process operates similarly to a cron job, allowing synchronization tasks to be scheduled at regular intervals. This type is ideal for systems that require periodic updates to ensure data and configuration consistency over time without the need for real-time accuracy.

LiveSynchronization

LiveSynchronization provides real-time synchronization, continuously monitoring and updating data and configurations as changes occur. This type of synchronization is essential for environments where immediate consistency and up-to-date information are crucial.

This option minimises RPO and RTO due to the minimal amount of data lost before a disaster and the low overhead and wait time to restart operations in the new instance.

Resume

Prerequisites

Before initiating the Synchronization process, ensure the following prerequisites are met:

• Both source and destiation systems have been defined as Asset.
• There is a network connectivity between the assets and the operator.

2 - Kubernetes/OpenShift

2.1 - Introduction

You can synchronize Kubernetes objects between two clusters.

Supported models

LiveSynchronization

The Kubernetes objects are syncrhonized in real-time between the defined clusters using the LiveSynchronization Kubernetes object.

Architecture

The sychronization can be executed from inside one of the clusters you want to synchronize (2-clusters architecture) or from a third clusters (3-clusters architecture).

2-clusters architecture

This configuration is recommended for training, testing, validation or when the 3-clusters option is not optimal or possible.

The currently active cluster will be the source cluster, while the passive is the destination cluster. The operator, including all the Custom Resource Definitions (CRD) and processes, is installed in the latter. The operator will listen for new resources that fulfill the requirements and clone them into the destination cluster.

The source cluster is never aware of the destination cluster and can exist and operate as normal without its presence. The destination cluster needs to have access to it through a KubernetesCluster resource.

3-clusters architecture

In addition of the already existing 2 clusters, this modality includes the management cluster. The operator synchronization workflow is delegated in it instead of depending on the destination cluster. The management cluster is in charge of reading the changes and new resources in the source cluster and syncing them to the destination. Neither source or destination cluster needs to know of the existence of the management cluster and can operate without it. Having a separate cluster that is decoupled from direct production activity lowers operational risks and eases access control to both human and software operators. The operator needs to be installed in the destination cluster as well to start the recovery process without depending on other clusters. Custom Resources that configure the synchronization are deployed in the management cluster while those only relevant when executing the recovery process are deployed in the destination cluster.

This structure fits organizations that are already depending on a management cluster for other tasks or ones that are planning to do so. Resiliency Operator does not require a standalone management cluster and can be installed and managed from an existing one.

2.2 - Configuring a LiveSynchronization

Introduction

A LiveSynchronization resource indicates a set of Kubernetes resource to replicate or synchronize between the source cluster and the destination cluster.

Requirements

• Create a KubernetesCluster resource for the source cluster.
• Create a KubernetesCluster resource for the destination cluster.

Process

1. Configure the live synchronization

Create the livesynchronization.yaml file according to your requirements. For this example, the goal is to synchronize deployments with the disaster-recovery label set to enabled. It is also desirable that when its replication is completed that no pod is created in the destination cluster and that after a recovery is launched the deployment launches active pods again.

Let’s dissect the following YAML:

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: livesynchronization-sample
spec:
  suspend: false
  plugin: kubernetes-objects-to-kubernetes
  config:
    sourceName: source
    destinationName: destination
    observability:
      enabled: false
    replication:
      resources:
        - group: apps
          version: v1
          resource: deployments
          transformation:
            patch:
              - op: replace
                path: /spec/replicas
                value: 0
          filters:
            namespaceSelector:
              matchLabels:
                disaster-recovery: enabled
          recoveryProcess:
            fromPatch:
              - op: replace
                path: /spec/replicas
                value: 1

spec.config.sourceName and spec.config.destinationName refers to the name and namespace of the KubernetesCluster resources for the corresponding clusters.

The spec.config.replication.resources is a list of the set of resources to deploy. A single LiveSynchronization can cover multiple types or groups of resources, although this example only manages deployments.

The type of the resource is defined at spec.config.replication.resources[*].resource. The filters can be located in spec.config.replication.resources[*].filters. In this case, the RecoveryPlan is matching the content of the disaster-recovery label.

The spec.config.replication.resources[*].transformation and spec.config.replication.resources[*].recoveryProcess establish the actions to take after each resource is synchronized and after they are affected by the recovery process respectively. In this case, while being replicated, each deployment will set their replicas to 0 in the destination cluster and will get back to one after a successful recovery. The resource parameters are always left intact in the source cluster.

2. Suspending and resumen a recovery plan

A keen eye might have noticed the spec.suspend parameter. In this example it is set to true to indicate that the recovery plan is inactive. An inactive or suspended recovery plan will not replicate new or existing resources until it is resumed. Resuming a recovery plan can be done by setting spec.suspend to false and applying the changes in yaml. Alternatively, a patch with kubectl will work as well and will not require the original yaml file:

kubectl patch livesynchronization <livesynchronization_name> -p '{"spec":{"suspend":false}}' --type=merge

3. Deploy the Live Synchronization

The live synchronizarion can be deployed as any other Kubernetes resource:

kubectl -n <namespace_name> apply -f livesynchronization.yaml

Additional steps

For more examples, take a look at our [samples](../../samples/kubernetes-objects-to-kubernetes" >}} “samples”).

Modifying synchronized resources.

Depending on the use case and the chosen solution for Resiliency Operator, it is convenient that resources synchronized in the destination cluster differ from the original copy. Taking as example a warm standby scenario, in order to optimize infrastructure resources, certain objects such as Deployments or Cronjobs do not need to be actively running until there is a disaster. The standby destination cluster can run with minimal computing power and autoscale as soon as the recovery process starts, reducing the required overhead expenditure.

While a resource is being synchronized into the destination cluster, its properties can be transformed to adapt them to the organization necessities. Then, if and when a disaster occurs, the resource characteristics can be restored to either its original state or an alternative one with the established recover process.

Filters

FIlters are useful to select only the exact objects to synchronize. They are set in the spec.config.replication.resources[*].filters parameter.

Name selector

The nameSelector filters by the name of the resources of the version and type indicated. The following example selects only the Configmaps that follow the regular expression config.*:

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: livesynchronization-sample
spec:
  plugin: kubernetes-objects-to-kubernetes
  suspend: false
  config:
    sourceName: source
    destinationName: destination
    observability:
      enabled: false
    replication:
      resources:
      - version: v1
        resource: configmaps
        filters:
          nameSelector:
            regex:
              - "config.*"

This selector can also be used negatively with excludeRegex. The following example excludes every configmap that ends in .test:

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: livesynchronization-sample
spec:
  plugin: kubernetes-objects-to-kubernetes
  suspend: false
  config:
    sourceName: source
    destinationName: destination
    observability:
      enabled: false
    replication:
      resources:
      - version: v1
        resource: configmaps
        filters:
          nameSelector:
            excludeRegex:
            - "*.test"

Namespace selector

The namespaceSelector filters resources taking in consideration the namespace they belong to. This selector is useful to synchronize entire applications if they are stored in a namespace. The following example selects every deployment that is placed in a namespace with the label disaster-recovery: enabled:

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: livesynchronization-sample
spec:
  plugin: kubernetes-objects-to-kubernetes
  suspend: false
  config:
    sourceName: source
    destinationName: destination
    observability:
      enabled: false
    replication:
      resources:
        - group: apps
          version: v1
          resource: deployments
          filters:
            selector:
              matchLabels:
                disaster-recovery: enabled

Transformations

Transformations are set in the spec.config.replication.resources[*].transformation parameter and are managed through patches.

Patch modifications alter the underlying object definiton using the same mechanism as kubectl patch. As with jsonpatch, the allowed operations are replace, add and remove. Patches are defined in the spec.config.replication.resources[*].transformation.patch list and admits an arbitary number of modifications.

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: livesynchronization-sample
spec:
  ...
  config:
    ...
    replication:
      resources:
      - ...
        transformation:
          patch:
            - op: replace
              path: /spec/replicas
              value: 0
            - op: remove
              path: /spec/strategy

RecoveryProcess

The RecoveryProcess of a LiveSynchronization is executed in the case of a disaster to recover the original status of the application in the destination cluster. A resource can be either restored from the original definition stored in a bucket or by performing custom patches like with Transformations.

To restore from the original data, read the Recovering from a Bucket section. This option will disregard performed transformations and replace the parameters with those of the source cluster.

Patching when recovering is accessible at spec.config.replication.resources[*].recoveryProcess.fromPatch list and admits an arbitary number of modifications. It will act on the current state of the resource in the destination cluster, meaning it will take into consideration the transformations performed when it was synchronized unlike when recovering from original. As with jsonpatch, the allowed operations are replace, add and remove.

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: livesynchronization-sample
spec:
  ...
  config:
    ...
    replication:
      resources:
        - ...
          recoveryProcess:
            fromPatch:
              - op: replace
                path: /spec/replicas
                value: 1

2.3 - Recovering from a Bucket

Introduction

A Bucket resource indicates an Object Storage that will be used to restore original objects when recovering from a disaster.

Object Storage stores data in an unstructured format in which each entry represents an object. Unlike other storage solutions, there is not a relationship or hierarchy between the data being stored. Organizations can access their files as easy as with traditional hierarchical or tiered storage. Object Storage benefits include virtually infinite scalability and high availability of data.

Many Cloud Providers include their own flavor of Object Storage and most tools and SDKs can interact with them as their share the same interface. Resiliency Operator officially supports the following Object Storage solutions:

AWS Simple Storage Service (S3) Google Cloud Storage

Resiliency Operator can support multiple buckets in different providers as each one is managed independently.

Contents stored in a bucket

A bucket is assigned to a LiveSynchronization by setting it in a spec.config.bucketName item. It stores every synchronized object in the destination cluster with some internal control annotations added. In the case of a disaster, resources with recoveryProcess.fromOriginal.enabled equal to true will be restored using the bucket configuration.

The path of a stored object is as follows: <bucket_namespace>/<bucket_name>/<object_group-version-resource>/<object_namespace>.<object_name>.

Requirements

• At least an instance of a ObjectStorage service in one of the supported Cloud Providers. This is commonly known as a bucket and will be referred as so in the documentation.
• At least one pair of accessKeyID and secretAccessKey that gives both write and read permissions over all objects of the bucket. Refer to the chosen cloud provider documentation to learn how to create and extract them. It is recommended that each access key pair has only access to a single bucket.

Preparing and setting the bucket

• Cloud Providers
• Google Cloud Storage
• Amazon Web Services S3

apiVersion: v1
kind: Secret
metadata:
  name: bucket-credentials
stringData:
  accessKeyID: <access_key_id>
  secretAccessKey: <secret_access_key>

apiVersion: assets.astronetes.io/v1alpha1
kind: Bucket
metadata:
  name: gcp
  namespace: <namespace>
spec:
  generic:
    endpoint: storage.googleapis.com
    name: <bucket_name>
    useSSL: true
    secretName: bucket-credentials

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: livesynchronization-sample
spec:
  plugin: kubernetes-objects-to-kubernetes
  config:
    sourceName: source
    destinationName: destination
    bucketName: <bucket_object_name>
    observability:
      enabled: false
    replication:
      resources:
        - group: apps
          version: v1
          resource: deployments
          transformation:
            patch:
              - op: replace
                path: /spec/replicas
                value: 0
          filters:
            namespaceSelector:
              matchLabels:
                env: pre
          recoveryProcess:
            fromPatch:
              - op: replace
                path: /spec/replicas
                value: 1
        - group: apps
          version: v1
          resource: deployments
          transformation:
            patch:
              - op: replace
                path: /spec/replicas
                value: 0
          filters:
            namespaceSelector:
              matchLabels:
                env: pre-second
          recoveryProcess:
            fromPatch:
              - op: replace
                path: /spec/replicas
                value: 1
        - group: ""
          version: v1
          resource: services
          filters:
            namespaceSelector:
              matchLabels:
                env: pre
        - group: ""
          version: v1
          resource: services
          filters:
            namespaceSelector:
              matchLabels:
                env: pre-second
        - group: ""
          version: v1
          resource: secrets
          filters:
            namespaceSelector:
              matchLabels:
                env: pre

apiVersion: v1
kind: Secret
metadata:
  name: bucket-credentials
stringData:
  accessKeyID: <access_key_id>
  secretAccessKey: <secret_access_key>

apiVersion: assets.astronetes.io/v1alpha1
kind: Bucket
metadata:
  name: gcp
spec:
  generic:
    endpoint: s3.<bucket-region>.amazonaws.com
    name: <bucket-name>
    useSSL: true
    secretName: bucket-credentials

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: livesynchronization-sample
spec:
  plugin: kubernetes-objects-to-kubernetes
  config:
    sourceName: source
    destinationName: destination
    bucketName: <bucket_object_name>
    observability:
      enabled: false
    replication:
      resources:
        - group: apps
          version: v1
          resource: deployments
          transformation:
            patch:
              - op: replace
                path: /spec/replicas
                value: 0
          filters:
            namespaceSelector:
              matchLabels:
                env: pre
          recoveryProcess:
            fromPatch:
              - op: replace
                path: /spec/replicas
                value: 1
        - group: apps
          version: v1
          resource: deployments
          transformation:
            patch:
              - op: replace
                path: /spec/replicas
                value: 0
          filters:
            namespaceSelector:
              matchLabels:
                env: pre-second
          recoveryProcess:
            fromPatch:
              - op: replace
                path: /spec/replicas
                value: 1
        - group: ""
          version: v1
          resource: services
          filters:
            namespaceSelector:
              matchLabels:
                env: pre
        - group: ""
          version: v1
          resource: services
          filters:
            namespaceSelector:
              matchLabels:
                env: pre-second
        - group: ""
          version: v1
          resource: secrets
          filters:
            namespaceSelector:
              matchLabels:
                env: pre

2.4 - Understanding logging

Disaster Recovery Operator implements a logging system throughout all its pieces so that the end user can have visibility on the system.

JSON fields

Examples

An object read from the source cluster.

{
  "level": "info",
  "timestamp": "2023-11-28T18:05:26.904276629Z",
  "msg": "object read from cluster",
  "process": {
    "id": "eventslistener"
  },
  "sourceCluster": {
    "name": "source",
    "namespace": "dr-config",
    "resourceVersion": "91015",
    "uid": "3c39aaf0-4216-43a8-b23c-63f082b22436"
  },
  "sourceObject": {
    "apiGroup": "apps",
    "apiVersion": "v1",
    "name": "nginx-deployment-five",
    "namespace": "test-namespace-five",
    "resource": "deployments",
    "resourceVersion": "61949",
    "uid": "5eb6d1d1-b694-4679-a482-d453bcd5317f"
  },
  "oldSourceObject": {
    "apiGroup": "apps",
    "apiVersion": "v1",
    "name": "nginx-deployment-five",
    "namespace": "test-namespace-five",
    "resource": "deployments",
    "resourceVersion": "61949",
    "uid": "5eb6d1d1-b694-4679-a482-d453bcd5317f"
  },
  "lastUpdate": {
    "time": "2023-11-25T13:12:28.251894531Z",
    "userUID": "165d3e9f-04f4-418e-863f-07203389b51e",
    "username": "kubernetes-admin"
  },
  "event": {
    "type": "update"
  }
}

An object was uploaded to a recovery bucket.

{
  "level": "info",
  "timestamp": "2023-11-28T18:05:27.593493962Z",
  "msg": "object uploaded in bucket",
  "sourceObject": {
    "apiGroup": "apps",
    "apiVersion": "v1",
    "name": "helloworld",
    "namespace": "test-namespace-one",
    "resource": "deployments",
    "resourceVersion": "936",
    "uid": "7c2ac690-3279-43ca-b14e-57b6d57e78e1"
  },
  "oldSourceObject": {
    "apiGroup": "apps",
    "apiVersion": "v1",
    "name": "helloworld",
    "namespace": "test-namespace-one",
    "resource": "deployments",
    "resourceVersion": "936",
    "uid": "7c2ac690-3279-43ca-b14e-57b6d57e78e1"
  },
  "process": {
    "id": "processor",
    "consumerID": "event-processor-n74"
  },
  "bucket": {
    "name": "bucket-dev",
    "namespace": "dr-config",
    "resourceVersion": "91006",
    "uid": "47b50013-3058-4283-8c0d-ea3a3022a339"
  },
  "bucketObject": {
    "path": "dr-config/pre/apps-v1-deployments/test-namespace-one.helloworld"
  },
  "lastUpdate": {
    "time": "2023-11-25T13:12:29.625399813Z",
    "userUID": "165d3e9f-04f4-418e-863f-07203389b51e",
    "username": "kubernetes-admin"
  }
}

Managing logs

Messages structure vary depending on the operation that originated it.

The sourceCluster and destinationCluster are only present for operations that required direct access to either cluster. For the former, only messages originating from either the eventsListener, processor or reconciler services can include it in their logs. The latter will only be present in synchronizer or reconciler logs messages. These parameters will not be present for internal messages such as those coming from the nats since there is no direct connection with either cluster.

oldSourceObject is the previous state of the object when performing an update operation. It is not present in other types.

When the bucket and bucketObject parameters are present, the operation is performed against the indicated bucket without any involvement of the source and destination clusters. For create operations, an object was uploaded for the first time to the bucket, for updates an existing one is modified and for delete an object was deleted from the specified bucket.

These characteristics can be exploited to improve log searches by narrowing down the messages to those that are relevant at the moment. Serving as an example, the following command will output only those logs that affect the source managed cluster by filtering the messages that lack the sourceCluster.

kubectl -n dr-config logs pre-eventslistener-74bc689665-fwsjc | jq '. | select(.sourceCluster != null)'

This could be useful when trying to debug and solve connection issues that might arise.

Log messages

The log message is located in the msg parameter. It can be read and interpreted to establish the severity of the log. The following tables group every different log message depending on whether it should be treated as error or informative.

Error messages

Informative messages

2.5 - Resynchronization

Introduction

Due to particular circumstances it might be possible that there are objects that were not synchronized from the source cluster to the destination cluster. To cover this case, Resiliency Operator offers a reconciliation process that adds, deletes or updates objects in the destination cluster if its state differs from the source.

Architecture

Reconciliation is performed at the LiveSynchronization level. Every Live Synchronization is in charge of their covered objects and that they are up to date with the specification. Reconciliation is started by two components, EventsListener and Reconciler. The former is in charge of additive reconciliation and the latter of substractive reconciliation.

Additive reconciliation

Refers to the reconciliation of missing objects that are present in the source cluster but, for any reason, are not present or are not up to date in the destination cluster. The entry point is the EventsListener service which receives events with the current state in the source cluster of all the objects covered by the Recovery Plan with a period of one hour by default.

These resync events are then treated like regular events and follow the syncronization communication flow. If the object does not exist in the destination cluster, the Synchronizer will apply it. In the case of updates, only those with a resourceVersion greater than the existing one for that object will be applied, updating the definition of said object.

Substractive reconciliation

In the case that an object was deleted in the source cluster but it was not in the destination, the Additive Reconciliation will not detect it. The source cluster can send events containing the current state of its existing components, but not of those that ceased to exist in it.

For that, the Reconciler is activated with a period of one hour by default. It compares the state of the objects covered the Recovery Plan in both source and destination clusters. If a change is found, it creates a delete event in the NATS. This event is then processed as an usual delete event throughout the rest of the communication process.

Modifying the periodic interval

By default, the resynchronization process will be launched every hour. It can be changed by modifying the value at spec.config.resyncPeriod in the LiveSynchronization object. The admitted format is %Hh%Mm%Ss e.g. 1h0m0s for intervals of exactly one hour. Modifying this variable updates the schedule for both additive and substractive reconciliations.

apiVersion: automation.astronetes.io/v1alpha1
kind: LiveSynchronization
metadata:
  name: resync-3h-25m-12s
spec:
  ...
  config:
    replication:
      resyncPeriod: 3h25m12s

2.6 - Configuration reference

LiveSynchronization

Configuration

UserConfig

Resource

Transformation

PatchOpts

PatchOperation

Filters

RecoveryProcess

FromOriginal

ObservabilityConfig

Components

Component

2.7 - Components

Synchronization across clusters is managed through Kubesync, Astronetes solution for Kubernetes cluster replication. The following components are deployed when synchronization between two clusters is started:

2.8 - Granafa setup

Resiliency Operator offers the option of leveraging an existing Grafana installation to monitor the state of the synchronization and recovery process. Users can incorporate the provided visualizations to their workflows in a transparent manner without affecting their operability.

Prerequisites

Grafana Operator

The operator installation includes the necessary tools to extract the information from it. To view that information with the official dashboard, is required that the management cluster has the Grafana Operator installed.

Process

Create the Dashboard

Create the GrafanaDashboard from the release manifests:

kubectl apply -f https://astronetes.io/deploy/disaster-recovery-operator/v1.2/grafana-v5-dashboard.yaml

Working with the dashboard

The dashboard shows detailed information about the write, read and computing processes alongside a general overview of the health of the operator.

General view of the status of the operator:

The dashboard can be filtered attending the following characteristics:

• Namespace. Only shows information related to the LiveSynchronizations in a specified namespace.
• Recovery Plan. Filters by a specific LiveSynchronizaton.
• Object Namespace. Only shows information of the objects located in a given namespace regardless their associated LiveSynchronization.
• Object API Group. Objects are filtered attending to the API Group that they belong to.

Filters can be combined to get more specific results e.g. Getting the networking related objects that belong to a LiveSynchronization that is deployed in a namespace.

3 - Zookeeper

3.1 - Introduction

You can synchronize Zookeeper data between two clusters using the Zookeeper protocol.

Supported models

One time synchronization

You can synchronize the data just once with the Synchronization Kubernetes object.

Periodic synchronization

You can synchronize periodically the SynchronizationPlan Kubernetes object.

Samples

Synchronize once

Synchronize the data once only in the /test path:

apiVersion: automation.astronetes.io/v1alpha1
kind: Synchronization
metadata:
  generateName: synchronize-zookeeper-
spec:
  plugin: zookeeper-to-zookeeper-nodes
  config:
    sourceName: zookeeper-source
    destinationName: zookeeper-destination
    rootPath: /test
    createRoutePath: true

Scheduled synchronization

Synchronize data every hour in the /test path:

apiVersion: automation.astronetes.io/v1alpha1
kind: SynchronizationPlan
metadata:
  name: synchronize-zookeeper
spec:
  schedule: "0 * * * *"
  template:
    spec:
      plugin: zookeeper-to-zookeeper-nodes
      config: 
        sourceName: zookeeper-source
        destinationName: zookeeper-destination
        rootPath: /test

3.2 - Configuration

Synchronization

Configuration