How to fix NotPrimaryNoSecondaryOk: not primary and secondaryOk=false in MongoDB

MongoDBINTERMEDIATEMEDIUMUpdated Dec 18, 2025· 140 views

This error occurs when attempting to perform read operations on a MongoDB secondary replica set member without proper read preference configuration. By default, MongoDB restricts read operations to the primary node to ensure strict consistency.

Quick fix

Fixes NotPrimaryNoSecondaryOk

// In mongosh
rs.status()
rs.isMaster()
  1. Verify replica set status and current node role
  2. Configure read preference in connection string
  3. Set read preference in MongoDB driver
  4. Enable secondary reads in MongoDB shell
mongodb — error
// In mongosh
rs.status()
rs.isMaster()
NotPrimaryNoSecondaryOk: not primary and secondaryOk=false

What this error means

The "NotPrimaryNoSecondaryOk" error indicates that a read operation was attempted on a secondary member of a MongoDB replica set, but the connection or query was not configured to allow reading from secondaries. MongoDB uses the `secondaryOk` flag (or read preference settings in modern drivers) to control whether reads can be executed on non-primary nodes. By default, MongoDB directs all read operations to the primary member to ensure strict consistency, as the primary reflects the latest writes. Secondary members replicate data asynchronously from the primary, which means they may have slightly stale data. To read from secondaries, you must explicitly configure your connection or query to allow it. This error commonly occurs when connecting directly to a secondary node without setting the appropriate read preference, or when the replica set topology changes (such as during a failover) and the node you're connected to is no longer primary.

Typical symptoms

  • Read operations fail with NotPrimaryNoSecondaryOk error
  • Queries work on primary but fail on secondary members
  • Application cannot connect after replica set failover
  • Database queries throw 'not primary and secondaryOk=false' exception
  • MongoDB shell commands fail on secondary nodes

Common causes

  1. Connecting directly to a secondary replica set member without setting read preference
  2. Using default connection settings that restrict reads to primary only
  3. Replica set failover occurred and the connected node is no longer primary
  4. Driver or shell not configured with secondaryOk or appropriate read preference
  5. Attempting to run admin commands on secondary that require primary access
  6. Misconfigured replica set with incorrect IP addresses or hostnames

How to fix "NotPrimaryNoSecondaryOk: not primary and secondaryOk=false"

1Verify replica set status and current node role

First, check which node you're connected to and whether it's currently primary or secondary:

javascript
// In mongosh
rs.status()
rs.isMaster()

Look for the stateStr field in the output. If it shows "SECONDARY", you're connected to a secondary node and need to configure read preferences.

2Configure read preference in connection string

The recommended approach is to set the read preference in your MongoDB connection string:

javascript
// Node.js with MongoDB driver
const uri = "mongodb://host1:27017,host2:27017,host3:27017/mydb?replicaSet=myReplicaSet&readPreference=secondaryPreferred";

const client = new MongoClient(uri);

Read preference options:
- primary - Read only from primary (default)
- primaryPreferred - Read from primary, fall back to secondary if unavailable
- secondary - Read only from secondary members
- secondaryPreferred - Read from secondary, fall back to primary if none available
- nearest - Read from member with lowest network latency

3Set read preference in MongoDB driver

You can also configure read preference programmatically in your application code:

javascript
// Node.js MongoDB driver
const { MongoClient, ReadPreference } = require('mongodb');

const client = new MongoClient(uri);
await client.connect();

const db = client.db('myDatabase');
const collection = db.collection('myCollection', {
  readPreference: ReadPreference.SECONDARY_PREFERRED
});

// Or set at query level
const results = await collection.find({}).readPref('secondaryPreferred').toArray();
python
# Python PyMongo
from pymongo import MongoClient, ReadPreference

client = MongoClient('mongodb://localhost:27017/', replicaSet='myReplicaSet')
db = client.get_database('myDatabase', read_preference=ReadPreference.SECONDARY_PREFERRED)
collection = db.myCollection
4Enable secondary reads in MongoDB shell

If you're connecting directly to a secondary node using mongosh or the legacy mongo shell:

javascript
// In mongosh (MongoDB 5.0+)
db.getMongo().setReadPref('secondaryPreferred')

// Or for legacy mongo shell
rs.slaveOk()  // Deprecated but still works

After running this command, you'll be able to execute read queries on the secondary node.

5Use replica set connection string instead of direct connection

If you're connecting to a single host, switch to a replica set-aware connection string:

Instead of:

javascript
mongodb://secondary-host:27017/mydb

Use:

javascript
mongodb://primary-host:27017,secondary1:27017,secondary2:27017/mydb?replicaSet=myReplicaSet&readPreference=secondaryPreferred

This allows the driver to:
- Automatically discover all replica set members
- Handle failovers gracefully
- Route reads according to your preference
- Reconnect to the new primary if the topology changes

6Fix replica set configuration if misconfigured

If the error persists due to replica set misconfiguration (wrong IP addresses):

javascript
// Connect to the primary
mongosh "mongodb://primary-host:27017"

// Check current configuration
rs.conf()

// If IPs are incorrect, reconfigure
cfg = rs.conf()
cfg.members[0].host = "correct-ip-1:27017"
cfg.members[1].host = "correct-ip-2:27017"
cfg.members[2].host = "correct-ip-3:27017"
rs.reconfig(cfg)

For Docker environments, ensure the replica set configuration uses hostnames or IPs that are accessible from your application.

Advanced notes

Read Consistency Trade-offs:
When reading from secondaries, be aware that you may see stale data due to replication lag. Secondary members replicate asynchronously from the primary, typically with a lag of milliseconds to seconds depending on write load and network conditions. For applications requiring strong consistency, always use readPreference=primary.

Read Concern and Causal Consistency:
For applications that need to read their own writes from secondaries, use causal consistency sessions (MongoDB 3.6+):

javascript
const session = client.startSession({ causalConsistency: true });
await collection.insertOne({ ... }, { session });
const doc = await collection.findOne({ ... }, { session, readPreference: 'secondary' });
await session.endSession();

Tag Sets for Geographically Distributed Replica Sets:
You can configure read preferences to target specific replica set members using tags:

javascript
const readPreference = {
  mode: 'secondary',
  tags: [{ datacenter: 'east' }, { datacenter: 'west' }]
};

Hedged Reads (MongoDB 4.4+):
Enable hedged reads to send queries to multiple replica set members simultaneously and use the first response, reducing tail latency:

javascript
mongodb://host1:27017,host2:27017/?readPreference=nearest&hedged=true

Legacy Terminology:
Older MongoDB documentation and APIs may refer to slaveOk instead of secondaryOk. These terms are functionally equivalent, but modern drivers use "secondary" terminology. The rs.slaveOk() method is deprecated but still functional for backward compatibility.

Frequently asked questions

What does "NotPrimaryNoSecondaryOk" mean?
The "NotPrimaryNoSecondaryOk" error indicates that a read operation was attempted on a secondary member of a MongoDB replica set, but the connection or query was not configured to allow reading from secondaries. MongoDB uses the secondaryOk flag (or read preference settings in modern drivers) to control whether reads can be executed on non-primary nodes. By default, MongoDB directs all read operations to the primary member to ensure strict consistency, as the primary reflects the latest writes.
How do I fix "NotPrimaryNoSecondaryOk"?
This error occurs when attempting to perform read operations on a MongoDB secondary replica set member without proper read preference configuration. By default, MongoDB restricts read operations to the primary node to ensure strict consistency.
What causes "NotPrimaryNoSecondaryOk"?
Connecting directly to a secondary replica set member without setting read preference Using default connection settings that restrict reads to primary only Replica set failover occurred and the connected node is no longer primary
Is the "NotPrimaryNoSecondaryOk" error serious?
It is a medium-severity error — more of a blocker than a risk. The steps above resolve it.

Official resources & further reading