[Yandex Cloud documentation](../../index.md) > [Yandex Managed Service for OpenSearch](../index.md) > [Concepts](index.md) > Host roles

# Host roles in Managed Service for OpenSearch

Each Managed Service for OpenSearch cluster consists of one or more host groups of the `OpenSearch` and `Dashboards` (optional) types:

* An `OpenSearch` host group may contain hosts with the [DATA](#data) or [MANAGER](#manager) roles.
  
  The cluster must contain hosts with both roles. If a cluster has a single `OpenSearch` group, its hosts will have both roles.

* A `Dashboards` host group may only contain hosts with the [DASHBOARDS](#dashboards) role.

## Hosts with the DATA role {#data}

Hosts with this role store one or more indexes and handle search, write, and analysis queries.


For a cluster to be highly available and covered by a [service level agreement (SLA)](https://yandex.ru/legal/cloud_sla_mdb/), it must have two or more hosts with the `DATA` role.


[More on high-availability of clusters](high-availability.md).

### Use cases {#examples-data}

* [Migrating data from Elasticsearch](../tutorials/migration-to-opensearch.md)
* [Configuring an index policy in Managed Service for OpenSearch](../tutorials/opensearch-index-policy.md)
* [Configuring a cold storage policy in Managed Service for OpenSearch](../tutorials/opensearch-cold-storage-policy.md)
* [Loading data from Yandex Managed Service for OpenSearch to Yandex Object Storage using Yandex Data Transfer](../tutorials/opensearch-to-object-storage.md)
* [Using the yandex-lemmer plugin in Managed Service for OpenSearch](../tutorials/opensearch-yandex-lemmer.md)

## Hosts with the MANAGER role {#manager}

Hosts with this role monitor the state of the cluster and manage its configuration, ensuring the performance of all OpenSearch components.

If you are using hosts with the `MANAGER` role, a group containing three such hosts will be added to the cluster.

If no hosts with the `MANAGER` role are used, make sure to assign this role to the hosts with the `DATA` role. However, having dedicated hosts with the `MANAGER` role allows you to increase the overall cluster reliability and reduce the load on hosts with the `DATA` role.

{% note warning %}

If you add a host group with the `MANAGER` role to a cluster where this role is assigned to hosts with the `DATA` role, you will be unable to delete that group. The only way to restore the previous host configuration is to [restore the cluster from a backup](../operations/cluster-backups.md#restore).

{% endnote %}

## Hosts with the DASHBOARDS role {#dashboards}

Hosts with this role run OpenSearch Dashboards, a data visualization tool to use in such scenarios as real-time application monitoring, threat detection, incident management, or personalized search.

### Use cases {#examples-dashboards}

* [Authentication in OpenSearch Dashboards using Keycloak](../tutorials/saml-keycloak.md)
* [Uploading logs from Yandex Audit Trails](../tutorials/trails-to-opensearch.md)
* [Migrating data from Elasticsearch](../tutorials/migration-to-opensearch.md)