OpenSearch cluster fault tolerance

The fault tolerance of an OpenSearch managed database cluster is affected by:

• index replication;
• number of nodes in node groups with Manager and Data roles. For more details on node groups and their roles, see the OpenSearch Node Groups; guide.
• node allocation type in node groups.

Index replication

The cluster uses a standard index replication mechanism—for each primary shard, the number of replica shards specified during index creation is created. Writing to the index is performed only through primary shards, while reading can be performed simultaneously from both primary and replica shards.

Number of nodes in node groups

The node group with the Manager role contains three nodes. You cannot change the number of nodes in this group or add another node group with the Manager role.

The node group with the Data role consists of one node by default. To increase cluster fault tolerance, you can:

• increase the number of nodes in the group with the Data role in an existing cluster or when creating a cluster. You can add from one to ten nodes to each node group;
• add another node group with the Data role in an existing cluster or when creating a cluster. There can be no more than two node groups with the Data role in a cluster.

Node allocation type

The node allocation type in a cluster depends on:

• the number of nodes in a group;
• the type of pool where the cluster is located;
• the number of segments in the pool;
• configuration line.

You can view the list of pools and segments in the Servercore Infrastructure table in the Locations: countries, regions, availability zones, pools, and data center addresses guide.

Four node allocation types are available:

• Single-Segment;
• Multi-Segment;
• Single-AZ;
• Multi-AZ.

Single-Segment

Nodes are placed in the same segment of a single-zone pool. Applicable to:

• for single-node node groups;
• node groups with multiple nodes, if the cluster is located in a pool with only one segment;
• multi-node node groups in configurations of the HighFreq line.

note

For example, if you created a cluster in the ru-2 pool and used configurations from the HighFreq line for node groups with Manager and Data roles, all nodes of both groups will be placed in the same pool segment, for example, ru-2c.

Multi-Segment

Nodes are placed in different segments of a single-AZ pool. Applicable to multi-node node groups if the cluster is located in a pool with multiple segments.

Segments are located in different racks of the same data center. Nodes are distributed across segments sequentially.

note

For example, you created a cluster in the ru-1 pool and specified one node in the node group with the Data role. All three nodes of the group with the Manager role will be placed sequentially in the ru-1a, ru-1b, and ru-1c pool segments. The node of the group with the Data role will be placed in the ru-1a segment. If you add a second node to the group with the Data role, it will be placed in the ru-1b pool segment.

Single-AZ

Nodes are placed in the same segment of a multi-AZ pool. Applicable to:

• single-node node groups if the cluster is located in the ru-6 or uz-1 pools;
• multi-node node groups if the cluster uses a HighFreq line configuration and is located in the uz-1 pool.

note

For example, you created a cluster in the uz-1 pool and specified three nodes in a node group with the Data role. For the node groups with the Manager and Data roles, you used configurations from the HighFreq line. All nodes will be placed in the same pool segment, for example, in uz-1b.

Multi-AZ

Nodes are placed in different segments of a multi-AZ pool. Applicable to:

• multi-node node groups if the cluster is located in the ru-6 pool;
• multi-node node groups if the node groups do not use HighFreq line configurations and the cluster is located in the uz-1 pool.

Each pool segment is located in a separate data center. Nodes are distributed across segments sequentially.

note

For example, you created a cluster in the ru-6 pool and specified four nodes in a node group with the Data role. All three nodes of the groups with the Manager and Data roles will be placed sequentially in the ru-6a, ru-6b, and ru-6c pool segments. The fourth node of the group with the Data role will be placed in the ru-6a segment. If you add a fifth node to this group, it will be placed in the ru-6b pool segment.

Increase the number of nodes in a group with the Data role

You can add up to ten nodes to a node group with the Data role.

1. In the Control panel, in the top menu, click Products and select Managed Databases.
2. Open the Active tab.
3. Open the database cluster page → Settings tab.
4. In the menu of the node group with the Data role, select Edit configuration.
5. Specify the number of nodes in the group.
6. Click Save.

Add a node group with the Data role

The total number of node groups with the Data role in a cluster cannot exceed two.

1. In the Control panel, in the top menu, click Products and select Managed Databases.

2. Open the Active tab.

3. Open the database cluster page → Settings tab.

4. In the Cluster block, click Add node group.

5. Optional: change the node group name.

6. Select a node group with the Data role.

7. Select a configuration line.

8. If you selected a line with custom configurations, specify the number of vCPUs, RAM size, and disk size.

9. If you selected a line with fixed configurations, choose a configuration.

10. Specify the number of nodes in the group.

11. Optional: to make group nodes accessible from the Internet, select the Enable public access checkbox. A dedicated public IP address will be assigned to each node in the group.

    If the cluster subnet does not meet the requirements, enabling public access is unavailable. You can assign a public IP address after adding the group.

12. Click Save.