CODEWITHSUNDEEP
mongodbdatabase-replication
kk2449
kk2449

Reputation: 87

MongoDB replica set write when secondary down

I am trying to create a master-slave mongo instances. I created to instances:

mongod.exe --config "C:\mongodb\config\repl1.cfg"
mongod.exe --config "C:\mongodb\config\repl2.cfg"

Then I logged into my first node and created replicas, second node is started as well:

mongo.exe --port 27031
mongo.exe --port 27032


rs.initiate( {
   _id : "replKK",
   members: [
      { _id: 0, host: "localhost:27031", priority:5 },
      { _id: 1, host: "localhost:27032", hidden: true, priority:0 }
   ]
})

I can read and write when both nodes are up. But when I shut down the secondary node I can insert into collection, because I'm getting following error:

WriteCommandError({
        "topologyVersion" : {
                "processId" : ObjectId("6149c7170fc6426b073f16c3"),
                "counter" : NumberLong(11)
        },
        "ok" : 0,
        "errmsg" : "not master",
        "code" : 10107,
        "codeName" : "NotWritablePrimary",
        "$clusterTime" : {
                "clusterTime" : Timestamp(1632225689, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1632225689, 1)
})

What I am doing wrong? How can I achieve that first node is the instance that can insert rows and secondary is just kind of backup (master-slave)? I'm using MongoDB 5.0.3

Upvotes: 1

Views: 1625

Answers (1)

Wernfried Domscheit
Wernfried Domscheit

Reputation: 59456

In order to elect a writable PRIMARY node, the majority of all nodes must be up.

1 out of 2 is not the majority. Typical solution is to create an Arbiter. An Arbiter is a very lightweight mongod process, it does not store any data.

Upvotes: 1

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