Distributed: assign role to nodes (Master/Replica)

[lvca]

Assigning a role to servers can be useful to have read-only replicas avoiding any updates. Even the default is master, by assigning the role of replica allow to have many replicas around the network.

Where to define it? Not in the server configuration, to avoid hacking from users. It could be defined in distributed-config.json file. This could be the new default one:

{
    "autoDeploy": true,
    "hotAlignment": false,
    "offlineMsgQueueSize" : 0,
    "readQuorum": 1,
    "writeQuorum": 2,
    "failureAvailableNodesLessQuorum": false,
    "readYourWrites": true,
    "servers": { 
      "*": "master"
     },
    "clusters": {
        "internal": {
        },
        "index": {
        },
        "*": {
            "servers" : [ "<NEW_NODE>" ]
        }
    }
}

In this example we have 3 serves as master and we want to let to any other server that joins to be a merely slave:

{
    "autoDeploy": true,
    "hotAlignment": false,
    "offlineMsgQueueSize" : 0,
    "readQuorum": 1,
    "writeQuorum": 2,
    "failureAvailableNodesLessQuorum": false,
    "readYourWrites": true,
    "servers": { 
      "eur" : "master",
      "usa" : "master",
      "asia" : "master",
      "*": "replica"
     },
    "clusters": {
        "internal": {
        },
        "index": {
        },
        "*": {
            "servers" : [ "<NEW_NODE>" ]
        }
    }
}