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In this lesson, we’ll explore the distinct roles of voting and non-voting members in a Consul cluster. By default, server nodes participate in Raft’s leader election and maintain quorum. However, if you need additional read capacity without impacting election stability, add non-voting members. These nodes replicate the same data but are excluded from voting, boosting read throughput while preserving the Raft quorum.

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Comparison Table

Member TypeVotes in Raft ElectionData ReplicationPrimary Use Case
Voting MemberYesYesEnsures quorum, leader election, high availability
Non-voting MemberNoYesScales reads, redundancy zones, workload isolation
Use non-voting members to horizontally scale read operations in high-traffic environments without the risk of quorum changes.

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Configuring a Non-voting Member

You can designate a node as non-voting in two ways:
  1. In the agent’s configuration file (consul.hcl): 
    # consul.hcl
non_voting = true
  2. Via the command line when starting the agent: 
    consul agent ... --non-voting-member
Be cautious not to overload your cluster with too many non-voting members, as excessive replication traffic can impact network resources.

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Example: Verifying Peers

Start with a three-node cluster where all servers are voters. List the Raft peers: 
$ consul operator raft list-peers
Node           ID               Address            State     Voter  RaftProtocol
Consul-Node-A  10.0.10.51:8300  10.0.10.51:8300    follower  true   2
Consul-Node-B  10.0.11.23:8300  10.0.11.23:8300    leader    true   3
Consul-Node-C  10.0.10.3:8300   10.0.10.3:8300     follower  true   2
Next, add a fourth node configured as a non-voting member. Re-run the command to see the updated list: 
$ consul operator raft list-peers
Node           ID               Address            State     Voter   RaftProtocol
Consul-Node-A  10.0.10.51:8300  10.0.10.51:8300    follower  true    2
Consul-Node-B  10.0.11.23:8300  10.0.11.23:8300    leader    true    3
Consul-Node-C  10.0.10.3:8300   10.0.10.3:8300     follower  true    2
Consul-Node-D  10.0.11.62:8300  10.0.11.62:8300    follower  false   2
Here, Consul-Node-D synchronizes all data without voting, providing extra read capacity while keeping the existing quorum intact.

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References

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