create index on existing collection on a MongoDB replica set (PRIMARY) - mongodb

Question

I want to add an index on an existing collection in a MongoDB replica set.
This replica set has only a Primary, at the moment, and is configured in this way to be able to use MongoDB change streams.
I log into Mongo shell using:
mongo -u <Account>
where <Account> is an account with role 'userAdminAnyDatabase '.
Then issue the commands:
use dbOfInterest
db.collectionOfInterest.createIndex({fieldOne:-1})
But after issuing the command above the console seems not responding anymore (after several minutes I had to stop it using CTRL+C).
The considered collection is a test one with very few documents.
What am I doing wrong?

Answer 1

Finally solved!!.
The issue is indeed related to "replica set node with auth can connect to itself" (more here).
I had to modify my mongod (file /etc/mongod.conf) configuration as follow:
# mongod.conf
# for documentation of all options, see:
# http://docs.mongodb.org/manual/reference/configuration-options/
# Where and how to store data.
storage:
dbPath: /var/lib/mongodb
journal:
enabled: true
# engine:
# mmapv1:
# wiredTiger:
# where to write logging data.
systemLog:
destination: file
logAppend: true
path: /var/log/mongodb/mongod.log
# network interfaces
net:
port: 27017
bindIp: 127.0.0.1
# how the process runs
processManagement:
timeZoneInfo: /usr/share/zoneinfo
security:
keyFile: /home/user1/Desktop/mongo.keyfile
authorization: enabled
#operationProfiling:
replication:
replSetName: AirHeritage
#sharding:
## Enterprise-Only Options:
#auditLog:
#snmp:
Note keyFile section into YAML mongod.conf file (pay attention to white spaces).
To correctly generate this mongo.keyfile I used:
openssl rand -base64 756 > <path-to-keyfile>
chmod 400 <path-to-keyfile>
Then do:
sudo chown mongodb:mongodb /home/user1/Desktop/mongo.keyfile
Check that results are something as:
ls -al /home/user1/Desktop/mongo.keyfile
-r-------- 1 mongodb mongodb 1024 gen 13 09:19 /home/user1/Desktop/mongo.keyfile
Then stop and restart mongod using:
sudo systemctl stop mongod
sudo systemctl start mongod
Check status:
sudo systemctl status mongod
● mongod.service - MongoDB Database Server
Loaded: loaded (/lib/systemd/system/mongod.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2021-01-13 09:25:59 CET; 44min ago
Docs: https://docs.mongodb.org/manual
Main PID: 10156 (mongod)
Memory: 348.6M
CGroup: /system.slice/mongod.service
└─10156 /usr/bin/mongod --config /etc/mongod.conf
gen 13 09:25:59 eanx-XPS-13-9350 systemd[1]: Started MongoDB Database Server.
Then log into mongo console as root (not sure it is necessary root, should suffice ClusterAdmin role):
mongo -u root
use dbOfInterest
db.collectionOfInterest.createIndex({field:1})
Having done all that before, index creation should have worked without hanging the console with a result as:
db.collectionOfInterest.createIndex({'field':1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"commitQuorum" : "votingMembers",
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1610526522, 5),
"signature" : {
"hash" : BinData(0,"qSqkVswHQA/IzWGYCd8HwNhXoQk="),
"keyId" : NumberLong("6877458498892857349")
}
},
"operationTime" : Timestamp(1610526522, 5)
}
To check MongoDB logs use:
sudo tail /var/log/mongodb/mongod.log | jq
(if not installed in your system use sudo apt install jq, jq is very useful to pretty print json files)
Finally check indexes on collection with:
db.collectionOfInterest.getIndexes()
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_"
},
{
"v" : 2,
"key" : {
"field" : 1
},
"name" : "field.name_1"
}
Note that two key fields are reported: "_id" (by default on collection creation) and "field"!!
Hope this can help someone else having a similar issue.
Only move the mongo.keyfile to a more suitable location (someone can suggest where?)

Answer 2

What you do is creating index "foreground" and that blocks usage of DB, until creation is ready.
You need to do it "background".
db.collectionOfInterest.createIndex({fieldOne:-1},{background:1})