NiFi Registry HA

NiFi Registry supports high availability (HA) through NIFI-8843. The Registry runs as a separate cluster alongside the NiFi cluster.

Architecture overview

                     ┌──────────────────────────────────────────┐
                     │            Apache ZooKeeper              │
                     │  /nifi-registry/leaders/registry-leader │
                     │  /nifi-registry/members/<nodeId>        │
                     │  /nifi-registry/cache-version/...       │
                     └──────────────────┬───────────────────────┘
                                        │ Curator / ZK client
             ┌──────────────────────────┼───────────────────────────┐
             │                          │                           │
  ┌──────────▼──────────┐  ┌────────────▼──────────┐  ┌────────────▼──────────┐
  │ NiFi Registry       │  │ NiFi Registry         │  │ NiFi Registry         │
  │ Node 0              │  │ Node 1                │  │ Node 2                │
  │ (LEADER)            │  │ (FOLLOWER)            │  │ (FOLLOWER)            │
  │                     │  │                       │  │                       │
  │ ┌─────────────────┐ │  │ ┌─────────────────┐   │  │ ┌─────────────────┐   │
  │ │ H2 Database     │ │  │ │ H2 Database     │   │  │ │ H2 Database     │   │
  │ │ (authoritative  │ │  │ │ (replica)       │   │  │ │ (replica)       │   │
  │ │ for writes)     │ │  │ └─────────────────┘   │  │ └─────────────────┘   │
  │ └─────────────────┘ │  │                       │  │                       │
  │                     │  │ WriteReplicationFilter│  │ WriteReplicationFilter│
  │ WriteReplicationFilter│ │ (307 → leader)       │  │ (307 → leader)       │
  │ (fan-out to followers)│ │                      │  │                       │
  └─────────────────────┘  └───────────────────────┘  └───────────────────────┘
             │                          ▲                           ▲
             └──── X-Registry-Replication fan-out ─────────────────┘

Traffic flows as follows:

• Reads – Any node serves read requests from its local H2 database.
• Writes to a follower – The follower returns 307 Temporary Redirect with the leader location. The client resends the request to the leader.
• Writes to the leader – The leader commits the write locally, then replicates it to all followers through internal X-Registry-Replication requests.

Coordination modes

NiFi Registry supports database and zookeeper coordination modes.

zookeeper

Recommendation: Use zookeeper mode when each node requires an isolated local H2 database. Use database mode when a shared RDBMS is available and ZooKeeper is not required.

Configure NiFi Registry HA

Configure the following properties in nifi-registry.properties on each Registry node.

# Enable HA
nifi.registry.cluster.enabled=true
nifi.registry.cluster.coordination=zookeeper
# Node identity
nifi.registry.cluster.node.identifier=registry-node-1
nifi.registry.cluster.node.address=https://node1:18443
# Shared internal authentication token
# Use the same token on all nodes. The token must contain at least 64 hexadecimal characters.
nifi.registry.cluster.node.internal.auth.token=<64-character-hex-string>
# ZooKeeper configuration for zookeeper coordination mode
nifi.registry.cluster.zookeeper.connect.string=zk1:2181,zk2:2181,zk3:2181
nifi.registry.cluster.zookeeper.root.node=/nifi-registry
# Cache polling interval for database coordination mode
nifi.registry.cluster.cache.refresh.interval.ms=15000
# HTTPS
nifi.registry.web.https.host=<this-node-hostname>
nifi.registry.web.https.port=18443

Set nifi.registry.cluster.coordination=database to use database coordination.

Use a unique value for nifi.registry.cluster.node.identifier and the correct node URL for nifi.registry.cluster.node.address on each node.

Custom Ambari Commands

The ambari-mpack provides the following custom commands for NiFi Registry maintenance:

• ENABLE_READONLY_MODE – Activates MaintenanceModeFilter. The Registry rejects write requests with 503 Service Unavailable and continues to serve read requests. Run this command before planned maintenance.
• DISABLE_READONLY_MODE – Deactivates maintenance mode and resumes write processing.

HA database tables

Database coordination uses the following HA tables.

-- Leader lease for database coordination mode.
CREATE TABLE CLUSTER_LEADER (
 id VARCHAR(100) PRIMARY KEY, -- Always 'SINGLETON'
 node_id VARCHAR(200) NOT NULL,
 acquired_at TIMESTAMP NOT NULL,
 expires_at TIMESTAMP NOT NULL -- 30-second TTL; renewed every 10 seconds
);
-- Authorization cache version for database coordination mode.
-- Increment this row to force all nodes to reload the authorization cache.
CREATE TABLE CACHE_VERSION (
 cache_name VARCHAR(200) PRIMARY KEY,
 version BIGINT NOT NULL DEFAULT 0
);
-- Cluster-wide event log.
-- Ensures that EventHookProvider fires exactly once.
CREATE TABLE REGISTRY_EVENT (
 id VARCHAR(50) PRIMARY KEY,
 event_type VARCHAR(100) NOT NULL,
 payload CLOB,
 created_at TIMESTAMP NOT NULL,
 processed_at TIMESTAMP
);