FAQ about Managed Service for MongoDB

General questionsGeneral questions

• What is Managed Service for MongoDB?

• What part of database management and maintenance is Managed Service for MongoDB responsible for?

• Which tasks are best addressed using Managed Service for MongoDB, and which using VMs with databases?

• What is a database host and database cluster?

• How do I get started with Managed Service for MongoDB?

• How many database hosts can there be in one cluster?

• How can I access a running DB host?

• How many clusters can I create within a single cloud?

• How are DB clusters maintained?

• Which MongoDB version does Managed Service for MongoDB use?

• What happens when a new DBMS version is released?

• What happens when a DBMS version becomes deprecated?

• How do you calculate usage cost for a database host?

• How can I change the computing resources and storage size for a database cluster?

• Is database host backup enabled by default?

• When are backups performed? Is a database cluster available during a backup?

• Can I change the retention period of automatic backups?

• What metrics and processes can be tracked using monitoring?

• How do I set up an alert that triggers as soon as a certain percentage of disk space has been used up?

Questions about MongoDBQuestions about MongoDB

• Why should I use MongoDB in Managed Service for MongoDB rather than my own VM-based installation?

• What happens to a cluster if one of its hosts fails?

• Can I deploy a MongoDB cluster in multiple availability zones?

• What is the backup procedure for MongoDB clusters?

• How does replication work for MongoDB?

• What limitations do MongoDB clusters have?

• Why is the cluster slow even though the computing resources are not used fully?

• How do I get access to the local.oplog.rs service collection?

• Can I connect to cluster hosts via SSH or get superuser permissions on hosts?

• What do I do if I get the revocation check error when using PowerShell to obtain an SSL certificate?

General questionsGeneral questions

What is Managed Service for MongoDB?What is Managed Service for MongoDB?

Managed Service for MongoDB is a service that helps you create, operate, and scale MongoDB databases in a cloud infrastructure.

With Managed Service for MongoDB, you can:

• Create a database with the required performance characteristics.
• Scale processing power and storage dedicated for your databases.
• Get database logs.

Managed Service for MongoDB takes on time-consuming MongoDB infrastructure administration tasks:

• Monitors resource usage.
• Automatically creates DB backups.
• Provides fault tolerance through automatic failover to backup replicas.
• Keeps database software updated.

You interact with database clusters in Managed Service for MongoDB the same way you interact with regular databases in your local infrastructure. This allows you to manage internal database settings to meet your app requirements.

What part of database management and maintenance is Managed Service for MongoDB responsible for?What part of database management and maintenance is Managed Service for MongoDB responsible for?

When you create clusters, Managed Service for MongoDB allocates resources, installs the DBMS, and creates databases.

For the created and running databases, Managed Service for MongoDB automatically creates backups and applies fixes and updates to the DBMS.

Managed Service for MongoDB also provides data replication between database hosts (both inside and between availability zones) and automatically switches the load over to a backup replica in the event of a failure.

Which tasks are best addressed using Managed Service for MongoDB, and which using VMs with databases?Which tasks are best addressed using Managed Service for MongoDB, and which using VMs with databases?

Yandex Cloud offers two ways to work with databases:

• Managed Service for MongoDB allows you to operate template databases with no need to worry about administration.
• Yandex Compute Cloud virtual machines allow you to create and configure your own databases. This approach allows you to use any database management systems, access databases via SSH, and so on.

What is a database host and database cluster?What is a database host and database cluster?

A database host is an isolated database environment in the cloud infrastructure with dedicated computing resources and reserved data storage.

A database cluster is one or more database hosts between which replication can be configured.

How do I get started with Managed Service for MongoDB?How do I get started with Managed Service for MongoDB?

Managed Service for MongoDB is available to any registered Yandex Cloud user.

To create a database cluster in Managed Service for MongoDB, you need to define its parameters:

• Host class (performance characteristics, such as CPUs, RAM, etc.).
• Disk type and size (reserved in full when creating a cluster).
• Network your cluster will be connected to.
• Number of hosts for the cluster and the availability zone for each of them.

For detailed instructions, see Getting started with Managed Service for MongoDB.

How many database hosts can there be in one cluster?How many database hosts can there be in one cluster?

The minimum number of hosts per cluster depends on the following:

• Selected platform and host class.
• Selected disk type.

The maximum number of hosts in a cluster is only limited by the requested computing resources and the size of the storage for the cluster.

For more information, see Quotas and limits.

How can I access a running DB host?How can I access a running DB host?

You can connect to Managed Service for MongoDB databases using standard DBMS methods.

Learn more about connecting to clusters.

How many clusters can I create within a single cloud?How many clusters can I create within a single cloud?

For more information on MDB technical and organizational limitations, see Quotas and limits.

How are DB clusters maintained?How are DB clusters maintained?

In Managed Service for MongoDB, maintenance implies:

• Automatic installation of DBMS updates and revisions for DB hosts (including disabled clusters).
• Changes to the host class and storage size.
• Other Managed Service for MongoDB maintenance activities.

For more information, see Maintenance.

Which MongoDB version does Managed Service for MongoDB use?Which MongoDB version does Managed Service for MongoDB use?

Managed Service for MongoDB supports MongoDB versions 5.0 and 6.0 Community Edition.

What happens when a new DBMS version is released?What happens when a new DBMS version is released?

When new minor versions are released, the cluster software is updated after a short testing period. Owners of the affected DB clusters are notified of expected work times and DB availability in advance.

What happens when a DBMS version becomes deprecated?What happens when a DBMS version becomes deprecated?

One month after the database version becomes deprecated, automatically sends email notifications to the owners of DB clusters created with this version.

New hosts can no longer be created using deprecated DBMS versions. Database clusters are automatically upgraded to the next supported version seven days after notification for minor versions and one month after notification for major versions. Deprecated major versions are going to be upgraded even if you have disabled automatic updates.

How do you calculate usage cost for a database host?How do you calculate usage cost for a database host?

In Managed Service for MongoDB, the usage cost is calculated based on the following parameters:

• Selected host class.
• Size of the storage reserved for the database host.
• Size of the database cluster backups. Backup size equal to the storage size is free of charge. Backup storage that exceeds this size is charged at special rates.
• Number of hours of database host operation. Partial hours are rounded to an integer value. You can find the cost per hour data for each host class in the Pricing policy section.

How can I change the computing resources and storage size for a database cluster?How can I change the computing resources and storage size for a database cluster?

You can change computing resources and storage size from the management console. All you need to do is choose a different host class for the required cluster.

The cluster characteristics change within 30 minutes. During this period, other maintenance activities may also be enabled for the cluster, such as installing updates.

Is database host backup enabled by default?Is database host backup enabled by default?

Yes, backup is enabled by default. For MongoDB, a full backup is performed once a day with the possibility to restore it to any saved backup.

By default, backups are stored for seven days.

When are backups performed? Is a database cluster available during backup?When are backups performed? Is a database cluster available during backup?

The backup window is an interval during which a full daily backup of the DB cluster is performed. The backup window is from 01:00 to 05:00 (UTC+3).

Clusters remain fully accessible during the backup window.

Can I change the retention period of automatic backups?Can I change the retention period of automatic backups?

You can set the retention period for automatic backups when creating or modifying a cluster.

What metrics and processes can be tracked using monitoring?What metrics and processes can be tracked using monitoring?

For all DBMS types, you can track:

• CPU, memory, network, or disk usage, in absolute terms.
• Memory, network, or disk usage as a percentage of the set limits for the corresponding cluster host class.
• Amount of data in the DB cluster and the remaining free space in the data storage.

For DB hosts, you can track metrics specific to the corresponding type of DBMS. For example, for MongoDB, you can track:

• Number of queries per second.
• Amount of disk space used.
• Number of connections, and so on.

Monitoring can be performed with a minimum granularity of five seconds.

How do I set up an alert that triggers as soon as a certain percentage of disk space has been used up?How do I set up an alert that triggers as soon as a certain percentage of disk space has been used up?

Create an alert with the disk.used_bytes metric in Yandex Monitoring. This metric shows the disk space usage in the Managed Service for MongoDB cluster.

For disk.used_bytes, use notification thresholds. The recommended values are as follows:

• Alarm: 90% of disk space
• Warning: 70% of disk space

Thresholds are set in bytes only. For example, the recommended values for a 100 GB disk are as follows:

• Alarm: 96636764160 bytes (90%)
• Warning: 75161927680 bytes (70%)

Questions about MongoDBQuestions about MongoDB

Why should I use MongoDB in Managed Service for MongoDB rather than my own VM-based installation?Why should I use MongoDB in Managed Service for MongoDB rather than my own VM-based installation?

Managed Service for MongoDB automates routine database maintenance:

• Quick DB deployment with the necessary available resources.
• Data backup.
• Regular software updates.
• Providing DB cluster failover.
• Database usage monitoring and statistics.

What happens to a cluster if one of its hosts fails?What happens to a cluster if one of its hosts fails?

If there are more than one replica in the database cluster, it will continue working if a host fails.

The only way data may be lost is if the cluster's only host fails.

Can I deploy a MongoDB cluster in multiple availability zones?Can I deploy a MongoDB cluster in multiple availability zones?

Yes. A database cluster may consist of hosts that reside in different availability zones and even different availability regions.

What is the backup procedure for MongoDB clusters?What is the backup procedure for MongoDB clusters?

Backups are created every 24 hours and stored for seven days after being created. You can restore data only as of the backup creation time.

How does replication work for MongoDB?How does replication work for MongoDB?

Managed Service for MongoDB uses the standard MongoDB replication mechanism: if a cluster has more than one active host, one of them is automatically selected as the primary server to handle write requests.

For more information about how replication works in MongoDB, read the relevant documentation.

What limitations are imposed on MongoDB database clusters?What limitations are imposed on MongoDB database clusters?

For more information on limits in Managed Service for MongoDB, see Quotas and limits.

Why is the cluster slow even though the computing resources are not used fully?Why is the cluster slow even though the computing resources are not used fully?

Perhaps, the maximum storage IOPS and bandwidth values are insufficient for processing the current number of requests. In this case, throttling is triggered and the performance of the entire cluster degrades.

The maximum IOPS and bandwidth values increase by a fixed value when the storage size increases by a certain step. The step and increment values depend on the disk type:

To increase the maximum IOPS and bandwidth values and make throttling less likely, increase the storage size when you update your cluster.

If you are using the network-hdd storage type, consider switching to network-ssd or network-ssd-nonreplicated by restoring the cluster from a backup.

How do I get access to the local.oplog.rs service collection?How do I get access to the local.oplog.rs service collection?

To grant a user read access to oplog, assign them the mdbReplication role in the admin database. To do this, run the following command in the Yandex Cloud CLI:

yc managed-mongodb user update <username> \
  --cluster-name <cluster_name> \
  --permission database=admin,role=mdbReplication,role=<other_role>,... \
  --permission database=<other_DB_name>,role=<role>,...

To avoid deleting user roles that are already assigned, list both the existing and new roles in the command.

Can I connect to cluster hosts via SSH or get superuser permissions on hosts?Can I connect to cluster hosts via SSH or get superuser permissions on hosts?

You cannot connect to hosts via SSH, nor can you get superuser permissions. This is done for the sake of security and user cluster fault tolerance because direct changes inside a host can render it completely inoperable.

What do I do if I get the revocation check error when using PowerShell to obtain an SSL certificate?What do I do if I get the revocation check error when using PowerShell to obtain an SSL certificate?

Here is the full text of the error:

curl: (35) schannel: next InitializeSecurityContext failed: Unknown error (0x80092012)
The revocation function was unable to check revocation for the certificate

This means, when connecting to the website, the service failed to check whether or not the website’s certificate is on the list of revoked certificates.

To fix this error:

• Make sure the corporate network settings do not block the check.

• Run the command with the --ssl-no-revoke parameter.

   mkdir $HOME\.mongodb; curl.exe --ssl-no-revoke -o $HOME\.mongodb\root.crt https://storage.yandexcloud.net/cloud-certs/CA.pem