Single Instance Mongodb Replica Set - cannot perform query/insert operations

As above answers said, the config is not set correctly.

I tried to re-init the replica, but got the error msg:

singleNodeRepl:OTHER> rs.initiate({ _id: "rs0", members: [ { _id: 0, host : "localhost:27017" } ] } )
{
    "info" : "try querying local.system.replset to see current configuration",
    "ok" : 0,
    "errmsg" : "already initialized",
    "code" : 23,
    "codeName" : "AlreadyInitialized"
}

The solution is to reconf the mongo:

singleNodeRepl:OTHER> rsconf = rs.conf()
singleNodeRepl:OTHER> rsconf.members = [{_id: 0, host: "localhost:27017"}]
[ { "_id" : 0, "host" : "localhost:27017" } ]
singleNodeRepl:OTHER> rs.reconfig(rsconf, {force: true})
{ "ok" : 1 }
singleNodeRepl:OTHER>
singleNodeRepl:SECONDARY>
singleNodeRepl:PRIMARY>

Short Answer:

I needed to do:

rs.initiate({_id:'rs0', version: 1, members: [{_id: 0, host:'localhost:27017'}]}

rather than rs.initiate().

Long Answer:

I am almost the same as @Madbreaks and @Yihe 's comment, but I was in the different background so that I'm adding my comment here.

Background

I used docker container of mongoDB and initiated the replicaset by rs.initiate(). (The data volume is mounted to the host, but it is out-of-topic here).

What Happend

When I restart the mongoDB container, the error "MongoError: not master and slaveOk=false" happened. Yes, the error message was different from @d0c_s4vage 's, but the workaround is the same as @Yihe 's.

Root Cause

The root cause was dynamically assigned hostname as follows:

rs0:PRIMARY> rs.conf()
{
    "_id" : "rs0",
    ...
    "members" : [
        {
            ...
            "host" : "ee4ed99b555e:27017",  # <----- !!!!

Where, the host "ee4..." above comes from docker container's internal hostname; this is set by my first rs.initiate(). This would be changed when recreate container. In my case, localhost is fine because of single server and single replicaset for 'rocketchat' app evaluation purpose.

Problem here is that you ran rs.initiate().. As EMPTY! You didn't tell what machines belongs to that replica set.

So..

rs.initiate({
      _id: "rs0",
      version: 1,
      members: [
         { _id: 0, host : "address.to.this.machine:27017" }
      ]
   }
)