AM-14456: Use case - Distribute MongoDB for MultiCloud (#218)

* updated sidebar/config

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* fixed typos

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* updated the service export steps

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* updated the prerequisites and description

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versioned_docs/version-1.3.0/use-cases/mongodb/overview.mdx

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+# Overview
+
+Businesses are increasingly adopting multi-cloud, hybrid-cloud, multi-k8s-cluster deployment strategy for their high 
+availability, disaster recovery, scalability, customer experience and regulatory compliance goals and to maximize the 
+service continuity and uptime. The strategy involves spreading the MongoDb (Postgres/other) database cluster across 
+multiple Kubernetes clusters deployed in multiple data centers, multiple clouds (regions/zones).
+
+KubeSlice can help realize the multi-cluster deployment strategy.
+
+KubeSlice combines network, application, and deployment services in a framework to create tenancy in a Kubernetes cluster and 
+extends it to multi-cluster.
+
+KubeSlice creates logical application boundaries known as slices that allow pods and services to communicate seamlessly across 
+clusters, clouds, edges, and data centers regardless of their physical location. Each slice is assigned its own set of namespaces, 
+resource quotas, traffic profiles that creates an isolated virtual network for each tenant (a team or a customer) in a single 
+cluster or multiple clusters. KubeSlice service discovery enables pods/services to discover and communicate with each other. 
+KubeSlice export/import mechanisms and KubeSlice meshDNS enables service discovery across the slice (across all the clusters 
+registered with slice).
+
+KubeSlice enables Kubernetes clusters to communicate over a slice specific overlay network enabling a seamless communication 
+across the database cluster members (replica sets). The members (replicas) can be distributed across multiple Kubernetes clusters 
+and are reachable over the slice overlay network using the member's FQDN address of the overlay network. By enabling a simplified 
+FQDN/DNS based communication across geographically distributed Kubernetes clusters KubeSlice enables MongoDB (database) cluster 
+members to communicate and coordinate the changes, streaming replication, replication, election, and so on to meet 
+resiliency, consistency and high availability requirements.
+
+KubeSlice creates a slice overlay network across all the clusters with slice VPN gateways and provides service discovery across 
+the slice to provide FQDN/IP based communication between Pods that are deployed on the slice.
+
+:::note
+KubeSlice does not require Istio or other service mesh to provide FQDN based service discovery across the clusters (across slice).
+:::
+
+MongoDB database deployment models can take advantage of KubeSlice connectivity and service discovery (FQDN based) across the 
+slice to spread database members (replica sets) across geographically distributed Kubernetes clusters.
+
+MongoDB (Postgres/other) supports several deployment models based on the business deployment strategy requirements: 
+multi-cloud, hybrid-cloud, multi-k8s-cluster deployment strategy for high-availability, disaster recovery, scalability, 
+customer experience and regulatory compliance goals and to maximize the service continuity and uptime.
+
+The following are some of the multi-cluster deployment models:
+
+- Single cloud/data center for high availability
+- Active/Standby deployment for DR in multiple clouds/data centers
+- Active/Active sharding based deployment for HA/scalability/in multiple clouds/data centers
+- Primary/Secondary replica sets for DR in multiple clouds/data centers
+
+KubeSlice slice can help with the above deployment models with its simplified multi-cluster connectivity
+
+- with secure slice overlay network and service discovery - between replica set members to achieve the MongoDB multi-cluster 
+deployment strategy requirements.
+
+The following figure shows the demo setup with mongoDB replica sets deployed over three clusters.
+
+![mongodb](/images/version1.3.0/use-cases/configure-mongodb/overview.png)

versioned_docs/version-1.3.0/use-cases/mongodb/replicas-access-methods.mdx

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+# Replica Access Methods
+
+Once the MongoDB replica sets are deployed over the slice across multiple clusters, there are different deployment models 
+that can be used to access the replicas.
+
+## Access Replicas from within the Clusters
+
+In this deployment model, services deployed in different namespaces within the same slice can access any of the replica sets for 
+read and write to the primary replica set.
+
+![mongodb](/images/version1.3.0/use-cases/configure-mongodb/replicaset-within-clusters.png)
+
+### Step 1: Create the mongo.sh Namespace on the Master Cluster
+
+ 1. On the master cluster, create the mongo-sh namespace using the following command:
+
+    ```
+    kubectl create ns mongo-sh
+    ```
+
+2. Onboard the namespace to the slice by applying the MongoDB slice configuration using the following command:
+
+   ``` 
+   kubectl apply -f examples/distributed-mongodb/mongodb-slice/mongodb-slice-lb-mongo-sh.yaml
+   ```
+
+### Step 2: Deploy a MongoDB Shell Pod in the mongo-sh Namespace
+
+Create and deploy a mongodb-sh pod in the mongo-sh namespace with the following configuration:
+
+```
+kubectl apply -f - <<EOF
+apiVersion: v1
+kind: Pod
+metadata:
+  name: mongodb-sh
+  namespace: mongo-sh
+spec:
+  containers:
+    - name: mongodb-shell
+      image: mongo:4.4.6 # You can adjust the version as needed
+      command: ["sleep"]
+      args: ["3600"]
+      stdin: true
+      tty: true
+EOF
+```
+
+### Step 3: Connect to the MongoDB Multi-Replica Set from the MongoDB Shell Pod
+
+1. Execute into the mongodb-sh container using the following command:
+
+
+   ```
+   kubectl exec -it mongodb-sh -c mongodb-shell -n mongo-sh -- sh
+   ```
+
+2. Inside the shell, connect to your MongoDB multi-replica set using the following command:
+
+   ```
+   mongo mongodb://multi-replica-set-0-0.mongodb.svc.slice.local:27017,multi-replica-set-1-0.mongodb.svc.slice.local:27017,multi-replica-set-2-0.mongodb.svc.slice.local:27017
+   ```
+
+
+
+   Example Output
+
+   ```
+   MongoDB shell version v4.4.6
+   connecting to: mongodb://multi-replica-set-0-0.mongodb.svc.slice.local:27017,multi-replica-set-1-0.mongodb.svc.slice.local:27017,multi-replica-set-2-0.mongodb.svc.slice.local:27017/?compressors=disabled&gssapiServiceName=mongodb
+   Implicit session: session { "id": UUID("5265d73a-ecde-4608-8fb6-713dd35203ff") }
+   MongoDB server version: 6.0.2
+   WARNING: shell and server versions do not match
+   Welcome to the MongoDB shell.
+   For interactive help, type "help".
+   For more comprehensive documentation, see
+	      https://docs.mongodb.com/
+    Questions? Try the MongoDB Developer Community Forums
+	        https://community.mongodb.com
+    ---
+    The server generated these startup warnings when booting: 
+            2024-10-16T13:55:22.237+00:00: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine. See http://dochub.mongodb.org/core/prodnotes-filesystem
+            2024-10-16T13:55:23.025+00:00: Access control is not enabled for the database. Read and write access to data and configuration is unrestricted
+            2024-10-16T13:55:23.025+00:00: vm.max_map_count is too low
+            2024-10-16T13:55:23.025+00:00:         currentValue: 524288
+            2024-10-16T13:55:23.025+00:00:         recommendedMinimum: 1677720
+            2024-10-16T13:55:23.025+00:00:         maxConns: 838860
+    ---
+    MongoDB Enterprise multi-replica-set:PRIMARY> 
+    ```
+
+### Step 4: Perform Write Operations in the MongoDB Shell
+
+After you are connected, you can perform write actions in the MongoDB shell and validate that the data is replicated across 
+your MongoDB replica set deployment.
+
+#### Disaster Recovery Failover
+
+When the primary replica set fails over to a secondary replica set, the services can connect to the new primary and 
+continue writing to it.
+
+## Access Replicas from outside the Cluster
+
+In this deployment model, MongoDB replicas will be offered as a service to external clients. The replica sets - primary and 
+secondary - are accessed from clients via MongoDB service access points.
+
+![mongodb](/images/version1.3.0/use-cases/configure-mongodb/replicaset-outside-clusters.png)
+
+MongoDB replica set services will be exposed via LB service in each cluster with each replica set with its own FQDN. MongoDB 
+clients can use the connection string to query the replica sets to determine the primary/secondary status of the replica sets 
+and connect to primary for writes and reads for any of the replicas. With appropriate global DNS LB policies the read requests 
+can connect to low-latency or geolocation based read replica set endpoints.

versioned_sidebars/version-1.3.0-sidebars.json

@@ -208,6 +208,40 @@
         "add-ons/add-ons-slack-metrics"
         ]
     },
+    {
+      "type": "category",
+      "label": "Use Cases",
+      "collapsed": true,
+      "link": {
+        "type": "generated-index",
+        "title": "use-case",
+        "description": "The use case section provides details the use cases applicable to kubeslice",
+        "keywords": [
+         "kubeslice"
+        ]
+      },
+      "items": [
+        {
+          "type": "category",
+          "label": "Distributed MongoDB",
+          "collapsed": true,
+          "link": {
+            "type": "generated-index",
+            "title": "use-case",
+            "description": "The use case section provides details the use cases applicable to kubeslice",
+            "keywords": [
+             "kubeslice"
+            ]
+          },
+
+        "items":[
+        "use-cases/mongodb/overview",
+        "use-cases/mongodb/distributed-mongodb-for-multicloud",
+        "use-cases/mongodb/replicas-access-methods"
+        ]
+        }
+      ]
+    },
 
     "troubleshooting/troubleshooting-guide", 
     {