Setup Mongo Replica Set for gate and mold

[yentsun]

A replica set needs to be setup

[yentsun]

How Mongo distiguish read/write members of replica set: https://docs.mongodb.com/manual/applications/replication/

We probably just need to define primary replica, which will have the write previledge.

[yentsun]

Write concern is set during doc insertion time (or in a global config).

• w: 1 means doc will be inserted into primary replica (probably what we need)
• w: "majority" means the doc insertion will wait for it to reach majority of replicas (not what we need)

[yentsun]

Read preference could be set to secondary to direct read operation to secondary replicas only https://docs.mongodb.com/manual/core/read-preference/

[yentsun]

Actual replicaset setup on local: https://docs.mongodb.com/manual/tutorial/deploy-replica-set-for-testing/

[yentsun]

Launching alpha (primary) replica:

C:\"Program Files"\MongoDB\Server\4.2\bin\mongod --replSet rs0 --port 27017 --bind_ip localhost --dbpath C:\mongoReplicas\alpha --oplogSize 128

bravo (secondary)

C:\"Program Files"\MongoDB\Server\4.2\bin\mongod --replSet rs0 --port 27018 --bind_ip localhost --dbpath C:\mongoReplicas\bravo --oplogSize 128

delta (secondary)

C:\"Program Files"\MongoDB\Server\4.2\bin\mongod --replSet rs0 --port 27019 --bind_ip localhost --dbpath C:\mongoReplicas\delta --oplogSize 128

ReplicaSet config:

rsconf = {
    _id: "rs0",
    members: [
        { _id: 0,
          tags: { name: "alpha" },
          priority: 10,
          host: "localhost:27017" },

        { _id: 1,
          tags: { name: "bravo" },
          priority: 0,
          host: "localhost:27018" },

        { _id: 2,
          tags: { name: "delta" },
          priority: 0,
          host: "localhost:27019" }
    ]
}

[yentsun]

TODO:

• How to designate a primary replica