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Configure a Highly Available Ops Manager Application

The Ops Manager Application provides high availability through use of multiple Ops Manager Application servers behind a load balancer and through use of a replica set to host the Ops Manager Application Database.


Load Balancer

The Ops Manager Application’s components are stateless between requests. Any Ops Manager Application server can handle requests as long as all the servers read from the same Ops Manager Application Database. If one Ops Manager Application becomes unavailable, another fills requests.

To take advantage of this for high availability, configure a load balancer of your choice to balance between the pool of Ops Manager Application hosts. To do this in Ops Manager, perform the following actions:

  • Set the URL to Access Ops Manager property to the load balancer URL.

  • Set the Load Balancer Remote IP Header property to X-Forwarded-For, which is the HTTP header field the load balancer uses to identify the originating client’s IP address.


    If you are using a Layer-4 load balancer that does not support X-Forwarded-For by default, either enable X-Forwarded-For, or use Proxy Protocol.

The Ops Manager Application uses the client’s IP address for auditing, logging, and setting an access list for the API.

After the load balancer is configured and started, you should not log in to the Ops Manager Application from its individual host URLs.


To disallow access to each Ops Manager Application server, configure your firewall rules accordingly.


If you have two Ops Manager hosts serving the following URLs:


and put them behind a load balancer at the following URL:


After you configure and start that load balancer, you should not log in to Log in to instead.


If you set these parameters using the configuration file, change mms.remoteIp.header to the URL for the load balancer and mms.centralUrl to the URL for the Ops Manager host and port.

File System Snapshots Require Shared File System

If you configure Ops Manager to use multiple Ops Manager application servers behind an HTTP or HTTPS load balancer and use file system snapshots, FCV 4.2 or later backup snapshot jobs run in parallel on one or more servers. Ensure that you have a shared file system mounted on each Ops Manager server. The Ops Manager application server might open and write different offsets of the same files. Ensure that the shared file system allows this. Otherwise, you will encounter access errors.

Diagnostic Archive

To give your Ops Manager diagnostic archive time to generate, set the HTTP idle timeout parameter for the load balancer to 180 seconds.

Appliance Network Layer Support

Any load balancing appliance must support Layer 7 (the Application Layer) of the OSI model.

Replica Set for the Ops Manager Application Database

Deploy a replica set rather than a standalone to host the Ops Manager Application Database. Replica sets have automatic failover if the primary becomes unavailable.

If the replica set has members in multiple facilities, ensure that a single facility has enough votes to elect a primary if needed. Choose the facility that hosts the core application systems. Place a majority of voting members and all the members that can become primary in this facility. Otherwise, network partitions could prevent the set from being able to form a majority. For details on how replica sets elect primaries, see Replica Set Elections.

You can back up the replica set using file system snapshots. File system snapshots use system-level tools to create copies of the device that holds replica set’s data files.

To deploy the replica set that hosts the Ops Manager Application Database, see backing MongoDB instance.

The gen.key File

gen.key file is a 24-byte binary file used to encrypt and decrypt Ops Manager’s backing databases and user credentials. An identical gen.key file must be stored on every server that is part of a highly available Ops Manager deployment.

The gen.key file can be generated automatically or manually.

To have Ops Manager generate the file:
Start one Ops Manager server. Ops Manager will create a gen.key file if none exists.
To create the file manually:

Generate a 24-byte binary file.


The following creates the gen.key file using openssl:

openssl rand 24 > /<keyPath>/gen.key

Protect the gen.key file like any sensitive file. Change the owner to the user running Ops Manager and set the file permission to read and write for the owner only.

Once you have the gen.key file (either created automatically or manually), before starting the other Ops Manager servers, copy the file to the appropriate directory on the current server and to the appropriate directory on the other Ops Manager servers:

  • /etc/mongodb-mms/ for RPM or Ubuntu installations
  • ${HOME}/.mongodb-mms/ for archive (.tar) file installations


  • Any shared storage resource that stores the gen.key file should be configured for high availability so as not to introduce a potential single point of failure.
  • Any Ops Manager server that does not have the gen.key file installed cannot connect to the backing databases and become part of an HA Ops Manager instance.
  • Once you have generated the gen.key for your Ops Manager instance on the first Ops Manager server, back up the gen.key file to a secure location.

Upgrade Mode

If you have an Ops Manager installation with more than one Ops Manager host pointing to the same Application Database, you can upgrade Ops Manager to a newer version without incurring monitoring downtime. After you complete the upgrade of one Ops Manager host of a highly available Ops Manager deployment, that deployment enters a state known as Upgrade Mode. In this state, Ops Manager is available during an upgrade. The benefits of this mode are that throughout the upgrade process:

  • Alerts and monitoring operate
  • Ops Manager instances remain live
  • Ops Manager Application may be accessed in read-only mode
  • Ops Manager APIs that write or delete data are disabled

Your Ops Manager instance stays in Upgrade Mode until all Ops Manager hosts have been upgraded and restarted. You should not upgrade more than one Ops Manager host at a time.


Deploy the replica set that serves the Ops Manager Application Database. To deploy a replica set, see Deploy a Replica Set in the MongoDB manual.


The following procedure assumes you generated the first gen.key using one of the Ops Manager Application hosts. If you instead create your own gen.key, distribute it to the Ops Manager hosts before starting any of the Ops Manager Applications.


The load balancer placed in front of the Ops Manager Application servers must not return cached content. The load balancer must have caching disabled.

To configure multiple Ops Manager Applications with load balancing:


Configure a load balancer with the pool of Ops Manager Application hosts.

Configure the load balancer to perform a health check on each Ops Manager health API endpoint:


Ops Manager responds with one of two HTTP codes:

HTTP Status Code Health Status
200 Ops Manager host and application database appear healthy.

Ops Manager host or application database appear unhealthy.

See also

If this endpoint returns HTTP 500 often, review the Troubleshooting section.

The load balancer must not return cached content.


Configure Ops Manager to use the load balancer.

  1. In Ops Manager, click Admin, then the General tab, and then Ops Manager Config.

  2. Set the URL to Access Ops Manager property to point to the load balancer URL.

  3. Set the Load Balancer Remote IP Header property to the name of the HTTP header field the load balancer uses to identify the client’s IP address.

    Once Load Balancer Remote IP Header is set, Ops Manager enables the following HTTP headers:

    HTTP Header Forwards to Ops Manager
    X-Forwarded-Host Original host that the client requested in the Host HTTP request header.
    X-Forwarded-Proto Protocol used to make the HTTP request.
    X-Forwarded-Server Hostname of the proxy server.
    X-Proxied-Https HTTPS status of a request.

Update each Ops Manager Application host with the replication hosts information.

On each host, edit the file to set the mongo.mongoUri property to the connection string of the Ops Manager Application Database. You must specify at least 3 hosts in the mongo.mongoUri connection string.


Change the Ops Manager URL to the Load Balancer URL in the MongoDB Agent configuration file.

Complete the following steps on each MongoDB Agent’s host.

  1. Open the MongoDB Agent configuration file.

    vi /path/to/configurationFile.config

    The location of the Automation configuration file depends on your platform:

  2. Edit the mmsBaseUrl property to point to the load balancer and save the changes.

  3. Restart the MongoDB Agent.


Start one of the Ops Manager Applications.


If you installed the Ops Manager Application with an rpm or deb package, issue the following:

service mongodb-mms start

Copy the gen.key file to each Ops Manager host.

The gen.key file is located in /etc/mongodb-mms/ for installations from a package manager and in ${HOME}/.mongodb-mms/ for installations from an archive.

Copy the gen.key file from the running Ops Manager Application’s host to the appropriate directory on the other Ops Manager Application hosts.


Start the remaining Ops Manager Applications.

Additional Information

For information on making Ops Manager Backup highly available, see Configure a Highly Available Ops Manager Backup Service.