Configure Additional Options

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You can configure the following mongod runtime options on M10+ paid tier clusters.

Atlas dynamically modifies the Oplog Size for replica sets and sharded clusters. However, for the Minimum TLS Protocol Version and Allow Server-Side JavaScript settings, it performs a rolling restart of the shard members and the config server replica set. To learn more about how Atlas supports high availability during maintenance operations, see How does MongoDB Atlas deliver high availability?.

To view these settings, open the More Configuration Options under Additional Settings in the cluster form.

Modify the oplog size of the cluster.

For sharded cluster deployments, this modifies the oplog size of each shard in the cluster.

This option corresponds to modifying the replication.oplogSizeMB configuration file option for each mongod in the cluster.

Specify your desired Oplog Size in megabytes in the input box.


Reducing the size of the oplog requires removing data from the oplog. Atlas cannot access or restore any oplog entries removed as a result of oplog reduction. Consider the ramifications of this data loss before reducing the oplog.

  • You can't set the oplog to less than 990 megabytes.
  • Atlas places no upper limit in megabytes on the oplog. However, Atlas returns an error if the oplog size you choose leaves your cluster's disk with less than 25 percent of its capacity free.

To check the oplog size:

  1. Connect to your cluster via mongosh.
  2. Authenticate as a user with the Atlas admin role.
  3. Run the rs.printReplicationInfo() method.

Atlas displays the current oplog size and time.

Don't reduce the size of the oplog as a means of increasing available disk space. Only the oplog collection ( can reclaim the space saved by reducing the oplog size. Other collections do not benefit from reducing oplog storage.

Enable or disable enforcement of the 1024-byte index key limit. Documents can only be updated or inserted if, for all indexed fields on the target collection, the corresponding index entries do not exceed 1024 bytes.

If disabled, mongod writes documents that breach the limit but doesn't index them. This option corresponds to modifying the failIndexKeyTooLong parameter via the setParameter command for each mongod in the cluster.

Index Key Limit

failIndexKeyTooLong was deprecated in MongoDB version 4.2 and is removed in MongoDB 4.4 and later.

Enable or disable execution of operations that perform server-side execution of JavaScript.


In MongoDB version 4.4 and later, security.javascriptEnabled applies to mongos' as well.

Atlas cluster TLS certificates use IdenTrust's root Certificate Authority (DST Root CA X3) by default until April 30, 2021. Beginning on May 1, 2021, new TLS certificates that MongoDB Atlas creates will use ISRG instead of IdenTrust for their root Certificate Authority in line with Let's Encrypt's announcement of this transition. All DST Root CA X3 expire on September 30, 2021.

If you wish to use ISRG instead of IdenTrust:

  1. Select ISRG Root X1 from the drop-down.
  2. Review changes to your cluster and click Apply Changes.

    Atlas triggers a rolling restart of all the nodes in your cluster after 45 minutes when you switch between certificate roots. You can verify the change after the cluster restarts.

  3. (Optional) Run the following command to verify the change:

    echo | openssl s_client -showcerts -connect ${HOSTNAME}:${PORT} \
    2> /dev/null | grep -E "(Certificate|CN\s*=|O\s*=)"

    Set $HOSTNAME to a node hostname and $PORT to the port used to connect to MongoDB (usually 27017 or 27016). If you use Private Link to connect to your cluster, verify your cluster's port.

You can revert to DST if ISRG Root X1 causes any issues.


If you switch certificate root for a shared cluster, Atlas applies the change to all shared clusters in the same project.

Sets the minimum TLS version the cluster accepts for incoming connections. This option corresponds to configuring the net.ssl.disabledProtocols configuration file option for each mongod in the cluster.

TLS 1.0 Deprecation

For users considering this option as a method for enabling the deprecated Transport Layer Security (TLS) 1.0 protocol version, please read What versions of TLS does Atlas support? before proceeding. Atlas deprecation of TLS 1.0 improves your security of data-in-transit and aligns with industry best practices. Enabling TLS 1.0 for any Atlas cluster carries security risks. Consider enabling TLS 1.0 only for as long as required to update your application stack to support TLS 1.1 or later.

Enable or disable the execution of queries that require a collection scan to return results. This option corresponds to modifying the notablescan parameter via the setParameter command for each mongod in the cluster.

Sets the default level of acknowledgment requested from MongoDB for read operations for this cluster.

MongoDB 4.4 clusters default to /reference/read-concern-available.

Sets the default level of acknowledgment requested from MongoDB for write operations for this cluster.

MongoDB 4.4 clusters default to 1.

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