Each Managed Service for Elasticsearch cluster consists of one or more Elasticsearch hosts with different roles: Data node or Master node.
Dedicated hosts with the Data noderole
Hosts with this role store one or more indexes and handle search and analysis queries. To ensure index scalability and fault tolerance, configure sharding and replication for this index.
There should be at least one host with the Data node role in the cluster.
Dedicated hosts with the Master noderole
Hosts with this role monitor the state of the cluster and manage its configuration, ensuring the performance of all Elasticsearch components.
When using dedicated hosts with the Master node role, 3 such hosts are added to the cluster and you can't change their number.
If no hosts with the Master node role are used, this role will be supported by hosts with the Data node role. However, the presence of dedicated hosts with the Master node role increases the overall cluster reliability and reduces the load on hosts with the Data node role.