Scale a MongoDB Cluster Horizontally

DBaaS allows you to scale up and down the number of database replicas. Increased replica count may result in a cluster with improved availability, performance (capacity to handle more data reads), and fault tolerance for upgrades. A new IP address must be provided for each new instance. To do so, send a PATCH request with the new instances count (supported values are: 1, 3):

Endpoint

Use the following endpoint to request the new instance count: https://api.ionos.com/databases/mongodb/clusters/{clusterId}

Note: The sample UUID is d02de413-d5af-4104-a6f9-3a3c2766ee61.

Request

curl --include \
    --request PATCH \
    --user "[email protected]:Mb2.r5oHf-0t" \
    --header "Content-Type: application/json" \
    --data-binary '{
      "properties": {
        "instances": 3,
        "connections": [
          {
            "datacenterId": "b72ebcf5-6158-4ddb-8f65-31b20d82b6c7",
            "lanId": "2",
            "cidrList": [
              "10.7.222.3/24",
              "10.7.222.4/24",
              "10.7.222.5/24"
            ]
          }
       ]
      }
    }' 
    https://api.ionos.com/cloudapi/databases/mongodb/clusters/d02de413-d5af-4104-a6f9-3a3c2766ee61

Response

{
  "type": "cluster",
  "id": "d02de413-d5af-4104-a6f9-3a3c2766ee61",
  "metadata": {
    "state": "BUSY",
    "health": "HEALTHY",
    "createdDate": "2020-12-10T12:37:50.000Z",
    "createdBy": "[email protected]",
    "createdByUserId": "012342f-411f-1eeb-9d07-046c59cc737e"
  },
  "properties": {
    "type": "replicaset",
    "edition": "enterprise",
    "cores": 2,
    "ram": 2048,
    "storageSize": 10240,
    "storageType": "HDD",
    "displayName": "Represents database name",
    "location": "de/fra",
    "connections": [
      {
        "datacenterId": "b72ebcf5-6158-4ddb-8f65-31b20d82b6c7",
        "lanId": "2",
        "cidrList": [
          "10.1.1.3/24",
          "10.1.1.4/24",
          "10.1.1.5/24"
        ]
      }
    ],
    "instances": 3,
    "maintenanceWindow": {
      "time": "16:30:59",
      "dayOfTheWeek": "Monday"
    },
    "connectionString": "mongodb+srv://m-65f4a879f126e3c4.mongodb.de-fra.ionos.com"
  }
}

The patch example takes a previous cluster with one replica and adds two more replicas to it. The two new IP addresses are added to the connection properties cidrList, and the instances property receives the total number of replicas.

New servers are provisioned and added one at a time to the pool of replicas, implying an incremental rollout.

Downgrading a cluster follows the same pattern, with replica sets being removed one at a time and the desired replica set is reached.

Note: Only MongoDB Business edition provides an option to downscale the number of instances. Scaling down may result in one or more failovers and the disruption of open connections.

For more information, see Replica Set Elections.