Primary election isn't done after primary is killed on a MongoDB Cluster - mongodb

Question

I try to test fail over scenario of a mongoDB cluster. When I stopped the primary, I don't see any new primary election on my Java code's logs, and read/write operations are ignore and getting following:
No server chosen by ReadPreferenceServerSelector{readPreference=primary} from cluster description ClusterDescription{type=REPLICA_SET, connectionMode=MULTIPLE, serverDescriptions=[ServerDescription{address=mongo1:30001, type=UNKNOWN, state=CONNECTING, exception={com.mongodb.MongoSocketOpenException: Exception opening socket}, caused by {java.net.ConnectException: Connection refused (Connection refused)}}, ServerDescription{address=mongo2:30002, type=REPLICA_SET_SECONDARY, state=CONNECTED, ok=true, minWireVersion=0, maxWireVersion=8, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=3215664, setName='rs0', canonicalAddress=mongo2:30002, hosts=[mongo1:30001], passives=[mongo2:30002, mongo3:30003], arbiters=[], primary='null', tagSet=TagSet{[]}, electionId=null, setVersion=1, lastWriteDate=Fri Mar 26 02:08:27 CET 2021, lastUpdateTimeNanos=91832460163658}, ServerDescription{address=mongo3:30003, type=REPLICA_SET_SECONDARY, state=CONNECTED, ok=true, minWireVersion=0, maxWireVersion=8, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=3283858, setName='rs0', canonicalAddress=mongo3:30003, hosts=[mongo1:30001], passives=[mongo2:30002, mongo3:30003], arbiters=[], primary='null', tagSet=TagSet{[]}, electionId=null, setVersion=1, lastWriteDate=Fri Mar 26 02:08:27 CET 2021, lastUpdateTimeNanos=91832459878686}]}. Waiting for 30000 ms before timing out
I am using the following config:
var cfg = {
"_id": "rs0",
"protocolVersion": 1,
"version": 1,
"members": [
{
"_id": 0,
"host": "mongo1:30001",
"priority": 4
},
{
"_id": 1,
"host": "mongo2:30002",
"priority": 3
},
{
"_id": 2,
"host": "mongo3:30003",
"priority": 2,
}
]
};
rs.initiate(cfg, { force: true });
rs.secondaryOk();
db.getMongo().setReadPref('primary');
rs.isMaster() returns this:
{
"hosts" : [
"mongo1:30001"
],
"passives" : [
"mongo2:30002",
"mongo3:30003"
],
"setName" : "rs0",
"setVersion" : 1,
"ismaster" : true,
"secondary" : false,
"primary" : "mongo1:30001",
"me" : "mongo1:30001",
"electionId" : ObjectId("7fffffff0000000000000017"),
"lastWrite" : {
"opTime" : {
"ts" : Timestamp(1616719738, 1),
"t" : NumberLong(23)
},
"lastWriteDate" : ISODate("2021-03-26T00:48:58Z"),
"majorityOpTime" : {
"ts" : Timestamp(1616719738, 1),
"t" : NumberLong(23)
},
"majorityWriteDate" : ISODate("2021-03-26T00:48:58Z")
},
"maxBsonObjectSize" : 16777216,
"maxMessageSizeBytes" : 48000000,
"maxWriteBatchSize" : 100000,
"localTime" : ISODate("2021-03-26T00:49:08.019Z"),
"logicalSessionTimeoutMinutes" : 30,
"connectionId" : 28,
"minWireVersion" : 0,
"maxWireVersion" : 8,
"readOnly" : false,
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1616719738, 1),
"signature" : {
"hash" : BinData(0,"/+QXGSyYY+M/OXbZ1UixjrDOVz4="),
"keyId" : NumberLong("6942620613131370499")
}
},
"operationTime" : Timestamp(1616719738, 1)
}
Here what I see is hosts list has primary node and passives list have the secondries. I don't know when is the case that all nodes are considered under hosts in a cluster setup, so passives will be empty. The only related info I found is priority of the secondries should not be 0. Otherwise they won't be considered as candidate for the primary election.
"mongo1:30001"
],
"passives" : [
"mongo2:30002",
"mongo3:30003"
],...

Answer 1

From the docs:
isMaster.passives
An array of strings in the format of "[hostname]:[port]" listing all members of the replica set which have a members[n].priority of 0.
This field only appears if there is at least one member with a members[n].priority of 0.
Those nodes have been set to priority 0 somehow, and will therefore never attempt to become primary.