Set up a quorum node

To reduce infrastructure costs, you can set up a quorum-only node with minimal resources.

Clusters require an odd number of nodes to maintain quorum and avoid split-brain scenarios when making decisions. If you need to add another node to a cluster for quorum but want to provision fewer resources and reduce infrastructure costs, you can set up a quorum node instead of a regular node.

Quorum nodes participate in cluster quorum decisions and can act as a tiebreaker. However, they do not host database shards or endpoints, which reduces their resource requirements. A quorum node should have at least 2 cores and 8 GB of RAM. See the hardware requirements for more details and considerations.

Enable quorum_only setting

1. Run rladmin status nodes and find a node with no shards.

   In the following example, nodes without shards have 0/100 for the SHARDS column.

   $ rladmin status nodes
   CLUSTER NODES:
   NODE:ID    ROLE      ADDRESS             EXTERNAL_ADDRESS        HOSTNAME                SHARDS    CORES         FREE_RAM            PROVISIONAL_RAM        VERSION           STATUS
   node:1     master    192.0.2.0                                   3d99db1fdf4b            0/100     2             6.33GB/7.79GB       4.93GB/6.39GB          7.8.6-36          OK
   node:2     slave     198.51.100.0                                b87cc06c830f            2/100     2             6.44GB/7.79GB       1.04GB/6.39GB          7.8.6-36          OK
   *node:3    slave     203.0.113.0                                 fc7a3d332458            0/100     2             6.45GB/7.79GB       4.93GB/6.39GB          7.8.6-36          OK
   

2. Enable quorum_only for the node using rladmin tune node:

   $ rladmin tune node <node-id> quorum_only enabled
   

3. Rerun rladmin status nodes to verify the quorum node shows 0/0 for SHARDS and 0KB/0KB for PROVISIONAL_RAM.

   $ rladmin status nodes
   CLUSTER NODES:
   NODE:ID    ROLE      ADDRESS             EXTERNAL_ADDRESS        HOSTNAME                SHARDS    CORES         FREE_RAM            PROVISIONAL_RAM        VERSION           STATUS
   node:1     master    192.0.2.0                                   3d99db1fdf4b            0/100     2             6.33GB/7.79GB       4.93GB/6.39GB          7.8.6-36          OK
   node:2     slave     198.51.100.0                                b87cc06c830f            2/100     2             6.44GB/7.79GB       1.04GB/6.39GB          7.8.6-36          OK
   *node:3    slave     203.0.113.0                                 fc7a3d332458            0/0       2             6.45GB/7.79GB       0KB/0KB                7.8.6-36          OK