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Disaster Recovery

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The Kubernetes Operator can orchestrate the recovery of MongoDB replica set members to a healthy Kubernetes cluster when the Kubernetes Operator identifies that the original Kubernetes cluster is down.

The Kubernetes Operator can orchestrate either an automatic or manual remediation of the MongoDBMultiCluster resources in a disaster recovery scenario, using one of the following modes:

  • Auto Failover Mode allows the Kubernetes Operator to shift the affected MongoDB replica set members from an unhealthy Kubernetes cluster to healthy Kubernetes clusters. When the Kubernetes Operator performs this auto remediation, it evenly distributes replica set members across the healthy Kubernetes clusters.

    To enable this mode, use --set multiCluster.performFailover=true in the MongoDB Helm Charts for Kubernetes. In the values.yaml file in the MongoDB Helm Charts for Kubernetes directory, the environment's variable default value is true.

    Alternatively, you can set the multi-Kubernetes cluster MongoDB deployment environment variable PERFORM_FAILOVER to true, as in the following abbreviated example:

    spec:
    template:
    ...
    spec:
    containers:
    - name: mongodb-enterprise-operator
    ...
    env:
    ...
    - name: PERFORM_FAILOVER
    value: "true"
    ...
  • Manual(plugin-based) Failover Mode allows you to use the MongoDB kubectl plugin to reconfigure the Kubernetes Operator to use new healthy Kubernetes clusters. In this mode, you distribute replica set members across the new healthy clusters by configuring the MongoDBMultiCluster resource based on your configuration.

    To enable this mode, use --set multiCluster.performFailover=true in the MongoDB Helm Charts for Kubernetes, or set the multi-Kubernetes cluster MongoDB deployment environment variable PERFORM_FAILOVER to false, as in the following abbreviated example:

    spec:
    template:
    ...
    spec:
    containers:
    - name: mongodb-enterprise-operator
    ...
    env:
    ...
    - name: PERFORM_FAILOVER
    value: "false"
    ...

Note

You can't rely on the auto or manual failover modes when a Kubernetes cluster hosting one or more Kubernetes Operator instances goes down, or the replica set member resides on the same failed Kubernetes cluster as the Kubernetes that manages it.

In such cases, to restore replica set members from lost Kubernetes clusters to the remaining healthy Kubernetes clusters, you must first restore the Kubernetes Operator instance that manages your multi-Kubernetes cluster MongoDB deployments, or redeploy the Kubernetes Operator to one of the remaining Kubernetes clusters, and rerun the kubectl mongodb plugin. To learn more, see Manually Recover from a Failure Using the MongoDB Plugin.

When a Kubernetes cluster hosting one or more Kubernetes Operator instances goes down, or the replica set member resides on the same failed Kubernetes cluster as the Kubernetes that manages it, you can't rely on the auto or manual failover modes and must use the following procedure to manually recover from a failed Kubernetes cluster.

The following procedure uses the MongoDB kubectl Plugin to:

  • Configure new healthy Kubernetes clusters.

  • Add these Kubernetes clusters as new member clusters to the mongodb-enterprise-operator-member-list ConfigMap for your multi-Kubernetes cluster MongoDB deployment.

  • Rebalance nodes hosting MongoDBMultiCluster resources on the nodes in the healthy Kubernetes clusters.

The following tutorial for manual disaster recovery assumes that you:

  • Deployed one central cluster and three member clusters, following the Multi-Kubernetes-Cluster Quick Start. In this case, the Kubernetes Operator is installed with the automated failover disabled with --set multiCluster.performFailover=false.

  • Deployed a MongoDBMultiCluster resource as follows:

    kubectl apply -n mongodb -f - <<EOF
    apiVersion: mongodb.com/v1
    kind: MongoDBMultiCluster
    metadata:
    name: multi-replica-set
    spec:
    version: 6.0.5-ent
    type: ReplicaSet
    persistent: false
    duplicateServiceObjects: true
    credentials: my-credentials
    opsManager:
    configMapRef:
    name: my-project
    security:
    tls:
    ca: custom-ca
    clusterSpecList:
    - clusterName: ${MDB_CLUSTER_1_FULL_NAME}
    members: 3
    - clusterName: ${MDB_CLUSTER_2_FULL_NAME}
    members: 2
    - clusterName: ${MDB_CLUSTER_3_FULL_NAME}
    members: 3
    EOF

The Kubernetes Operator periodically checks for connectivity to the clusters in the multi-Kubernetes cluster MongoDB deployment by pinging the /healthz endpoints of the corresponding servers. To learn more about /healthz, see Kubernetes API health endpoints.

In the case that CLUSTER_3 in our example becomes unavailable, the Kubernetes Operator detects the failed connections to the cluster and marks the MongoDBMultiCluster resources with the failedClusters annotation for subsequent reconciliations.

The resources with data nodes deployed on this cluster fail reconciliation until you run the manual recovery steps as in the following procedure.

To rebalance the MongoDB data nodes so that all the workloads run on CLUSTER_1 and CLUSTER_2:

1
kubectl mongodb multicluster recover \
--central-cluster="MDB_CENTRAL_CLUSTER_FULL_NAME" \
--member-clusters="${MDB_CLUSTER_1_FULL_NAME},${MDB_CLUSTER_2_FULL_NAME}" \
--member-cluster-namespace="mongodb" \
--central-cluster-namespace="mongodb" \
--operator-name=mongodb-enterprise-operator-multi-cluster \
--source-cluster="${MDB_CLUSTER_1_FULL_NAME}"

This command:

  • Reconfigures the Kubernetes Operator to manage workloads on the two healthy Kubernetes clusters. (This list could also include new Kubernetes clusters).

  • Marks CLUSTER_1 as the source of configuration for the member node configuration for new Kubernetes clusters. Replicates Role and Service Account configuration to match the configuration in CLUSTER_1.

2

Reconfigure the MongoDBMultiCluster resource to rebalance the data nodes on the healthy Kubernetes clusters by editing the resources affected by the change:

kubectl apply -n mongodb -f - <<EOF
apiVersion: mongodb.com/v1
kind: MongoDBMultiCluster
metadata:
name: multi-replica-set
spec:
version: 6.0.0-ent
type: ReplicaSet
persistent: false
duplicateServiceObjects: true
credentials: my-credentials
opsManager:
configMapRef:
name: my-project
security:
tls:
ca: custom-ca
clusterSpecList:
- clusterName: ${MDB_CLUSTER_1_FULL_NAME}
members: 4
- clusterName: ${MDB_CLUSTER_2_FULL_NAME}
members: 3
EOF

For an example of use of the MongoDB kubectl plugin in a GitOps workflow with Argo CD, see multi-cluster plugin example for GitOps.

GitOps recovery requires manual reconfiguration of Role Based Access Control using .yaml resource files. To learn more, see Understand Kubernetes Roles and Role Bindings.

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