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High Availability

Digital Rebar Provision supports High Availability (HA) deployments that reduce outage windows and protect against single-node failures. HA uses the RAFT consensus protocol to maintain consistent state across a cluster of DRP endpoint nodes.

Enterprise-licensed feature

High Availability (RAFT consensus clustering) is a licensed enterprise feature. Your RackN license must include the HA entitlement, and every endpoint plus the cluster's HA ID must be listed in the license. See Licensing.

HA Architecture

DRP HA is an active-passive configuration:

  • One node is the leader and handles all write operations
  • Remaining nodes are followers that replicate state from the leader
  • If the leader becomes unavailable, RAFT elects a new leader from the followers

Note

DRP HA cannot be used for read/write load sharing. All API write operations are handled by the leader. This simplifies consistency guarantees but means HA provides fault tolerance, not horizontal scaling.

For scaling guidance, see Scaling & Sizing.

RAFT Consensus

DRP uses the RAFT protocol on port 8093/tcp for:

  • Leader election when the current leader fails
  • Log replication — changes made to the leader are replicated to followers before being committed
  • Cluster membership — nodes join and leave the HA cluster through RAFT membership changes

All DRP nodes in an HA cluster must be able to communicate bi-directionally on port 8093.

Availability Zones

HA nodes can span availability zones to protect against zone-level failures. Considerations:

  • Odd node counts — RAFT requires a majority quorum. Use 3 or 5 nodes; 2 or 4 nodes provide no additional fault tolerance over 1 or 3
  • Network latency — High latency between zones increases write commit time; keep cross-zone latency low
  • Quorum requirements — A 3-node cluster tolerates 1 failure; a 5-node cluster tolerates 2 failures

State Replication

All DRP object data (machines, workflows, content packs, plugins, files) is replicated across HA nodes via RAFT. The only exception is the DRP binary version itself — nodes may run different versions during a rolling upgrade. Once upgraded, RAFT replicates any remaining content differences.

Manager Integration

When a DRP HA cluster is registered with a Manager, the Manager treats the entire HA cluster as a single logical endpoint. Configuration pushed via VersionSets is applied to the cluster; HA then replicates it across all nodes.

See Also