Feature Compatibility Version Issue

I want to add new servers to my replica set.
So I used rs.add("<IP>:<PORT>") to add the servers.
But the servers became not reachable. On checking Logs I found out it was feature compatibility version issue. So I updated the feature Compatibility Version using, db.adminCommand({ setFeatureCompatibilityVersion: "3.6" }).
But on checking status I got,

rspp1:PRIMARY> db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )
        "featureCompatibilityVersion" : {
                "version" : "3.4",
                "targetVersion" : "3.6"
        "ok" : 1,
        "$gleStats" : {
                "lastOpTime" : {
                        "ts" : Timestamp(1681888293, 1),
                        "t" : NumberLong(27)
                "electionId" : ObjectId("7fffffff000000000000001b")
        "$configServerState" : {
                "opTime" : {
                        "ts" : Timestamp(1681889207, 1),
                        "t" : NumberLong(5)

This means for some reason my upgrade is stuck and not finished.
I need a way to revert it back to 3.4.
Also db.adminCommand({ setFeatureCompatibilityVersion: "3.4" }) doesn’t work because the first upgrade is not completed yet.
I want ot stop the update and revert it back to 3.4
Kindly help me.

Hello @19_231_Chirag_Sharma,

I see that you are currently using an older version of MongoDB. The said version has reached its end of life (refer Legacy Support Policy). Therefore, it’s highly recommended that you upgrade to a newer version, such as 4.4.20, which is the latest stable release at the time of this writing.

To perform the upgrade, you can use the mongodump and mongorestore utilities to backup and restore your data. While there is no guarantee that this will work, it may be worth considering. However, before proceeding with the upgrade, it’s important to take a complete backup of your data to avoid any potential data loss.

  • Could you please provide more information on how you accessed the logs?
  • Did you happen to encounter any error messages? If so, could you kindly share the details?
  • Additionally, share the output of rs.conf() and rs.status() commands which can provide insights into the replica set’s configuration and status.
  • Also, can you share the upgrade steps you followed to upgrade and at what point it failed? Meanwhile, I’ll suggest you refer to Upgrade a Replica Set to 3.6.

Also, I’ll recommend using hostname instead of an actual IP address as per the recommendation in the documentation.