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Consul Enterprise’s Redundancy Zones feature partitions your server cluster into distinct fault domains—such as cloud availability zones or separate on-premise racks—to improve both scaling and high availability. By assigning exactly one voting server per zone and running additional non-voting peers alongside it, Consul ensures automatic promotion and maintains quorum if a voting member fails.
The image is a slide titled "Redundancy Zones," explaining the benefits of using non-voting servers for scaling and resiliency, and the process of promoting non-voting members if a voting member or zone fails.

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How Redundancy Zones Work

  1. Define fault domains (e.g., AZs or data center racks).
  2. Deploy one voting server and one or more non-voting servers in each zone.
  3. On voting-server failure, a non-voting peer is automatically promoted within the same zone.
Fault domains can be any logical grouping—availability zones, racks, or even geographic regions. This setup prevents a single domain failure from taking down your entire cluster.

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Example: Three Availability Zones

Imagine an AWS setup with three availability zones (AZ1, AZ2, AZ3) and a six-node Consul server cluster:
The image illustrates redundancy zones with voting and non-voting servers across three availability zones (AZ1, AZ2, AZ3), highlighting features like quorum and resiliency. It is labeled as an "Enterprise Feature" and includes a visual representation of server status.
Availability ZoneVoting ServersNon-Voting Servers
AZ111
AZ211
AZ311
  • If the voting server in AZ2 fails, its non-voting peer in AZ2 is promoted.
  • Quorum (3 of 5 voting servers) is maintained with one voting member in each zone.
  • Topology still spans three zones, giving you time to replace the failed node.

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Handling an Entire Zone Failure

If a entire zone (for example, AZ1) goes offline:
  • AZ2: 1 voting, 1 non-voting
  • AZ3: 1 voting, 1 non-voting
  • Quorum remains intact (2 of 3 voting servers), and Consul continues to serve requests.
The image illustrates redundancy zones with servers, highlighting a failed zone (AZ1) and showing that quorum and resiliency are maintained in AZ2 and AZ3. It emphasizes enterprise features with a focus on maintaining system integrity despite failures.
If two or more zones fail simultaneously, you risk losing quorum. Always monitor zone health and automate node replacements.

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Benefits of Using Redundancy Zones

  • High availability with cross-zone failover
  • Automated promotion of non-voting peers
  • Fault-domain isolation to prevent cascade failures
  • Simplified operations in multi-region or hybrid environments

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