E-R Model of Redis Cluster

The Redis module organizes Redis in production as clusters—logical entities composed of a group of Redis instances deployed on one or more nodes.

Each cluster is an autonomous high-performance cache/storage unit consisting of at least one Redis instance, exposing service capabilities through ports.

There are three core entities in Pigsty’s Redis module:

• Cluster: An autonomous Redis service unit serving as the top-level namespace for other entities.
• Instance: A single Redis server process running on a specific port on a node.
• Node: A hardware resource abstraction running Linux + Systemd environment, can host multiple Redis instances, implicitly declared.

Unlike PostgreSQL, Redis uses a single-node multi-instance deployment model: one physical/virtual machine node typically deploys multiple Redis instances to fully utilize multi-core CPUs. Therefore, nodes and instances have a 1:N relationship. Additionally, production typically advises against Redis instances with memory > 12GB.

Operating Modes

Redis has three different operating modes, specified by the redis_mode parameter:

• Standalone: Default mode, replication via replica_of parameter. Requires additional Sentinel cluster for HA.
• Sentinel: Stores no business data, dedicated to monitoring standalone Redis clusters for auto-failover; multi-node itself provides HA.
• Native Cluster: Data auto-sharded across multiple primaries, each can have multiple replicas, built-in HA, no sentinel needed.

Examples

Let’s look at concrete examples for each mode:

Standalone Cluster

Classic master-replica on a single node:

redis-ms:
  hosts:
    10.10.10.10:
      redis_node: 1
      redis_instances:
        6379: { }
        6380: { replica_of: '10.10.10.10 6379' }
  vars:
    redis_cluster: redis-ms
    redis_password: 'redis.ms'
    redis_max_memory: 64MB

Sentinel Cluster

Three sentinel instances on a single node for monitoring standalone clusters. Sentinel clusters specify monitored standalone clusters via redis_sentinel_monitor:

redis-sentinel:
  hosts:
    10.10.10.11:
      redis_node: 1
      redis_instances: { 26379: {}, 26380: {}, 26381: {} }
  vars:
    redis_cluster: redis-sentinel
    redis_password: 'redis.sentinel'
    redis_mode: sentinel
    redis_max_memory: 16MB
    redis_sentinel_monitor:
      - { name: redis-ms, host: 10.10.10.10, port: 6379, password: redis.ms, quorum: 2 }

Native Cluster

A Redis native distributed cluster with two nodes and six instances (minimum spec: 3 primaries, 3 replicas):

redis-test:
  hosts:
    10.10.10.12: { redis_node: 1, redis_instances: { 6379: {}, 6380: {}, 6381: {} } }
    10.10.10.13: { redis_node: 2, redis_instances: { 6379: {}, 6380: {}, 6381: {} } }
  vars:
    redis_cluster: redis-test
    redis_password: 'redis.test'
    redis_mode: cluster
    redis_max_memory: 32MB

This creates a 3 primary 3 replica native Redis cluster.

Identity Parameters

Pigsty uses the REDIS parameter group to assign deterministic identities to each Redis module entity. Three parameters are required:

With cluster name defined at cluster level and node number/instance definition assigned at node level, Pigsty automatically generates unique identifiers for each entity:

The Redis module does not assign additional identity to host nodes; nodes are identified by their existing hostname or IP address. redis_node is used for instance naming, not host node identity.

Instance Definition

redis_instances is a JSON object with port number as key and instance config as value:

redis_instances:
  6379: { }                                      # Primary instance, no extra config
  6380: { replica_of: '10.10.10.10 6379' }       # Replica, specify upstream primary
  6381: { replica_of: '10.10.10.10 6379' }       # Replica, specify upstream primary

Each Redis instance listens on a unique port within the node. You can choose any port number, but avoid system reserved ports (< 1024) or conflicts with Pigsty used ports. The replica_of parameter sets replication relationship in standalone mode, format '<ip> <port>', specifying upstream primary address and port.

Additionally, each Redis node runs a Redis Exporter collecting metrics from all local instances:

Redis’s single-node multi-instance deployment model has some limitations:

• Node Exclusive: A node can only belong to one Redis cluster, not assigned to different clusters simultaneously.
• Port Unique: Redis instances on the same node must use different ports to avoid conflicts.
• Password Shared: Multiple instances on the same node cannot have different passwords (redis_exporter limitation).
• Manual HA: Standalone Redis clusters require additional Sentinel configuration for auto-failover.

Monitoring Label System

Pigsty provides an out-of-box monitoring system that uses the above identity parameters to identify various Redis entities.

redis_up{cls="redis-ms", ins="redis-ms-1-6379", ip="10.10.10.10", job="redis"}
redis_up{cls="redis-ms", ins="redis-ms-1-6380", ip="10.10.10.10", job="redis"}

For example, the cls, ins, ip labels correspond to cluster name, instance name, and node IP—the identifiers for these three core entities. They appear along with the job label in all Redis monitoring metrics collected by VictoriaMetrics. The job name for collecting Redis metrics is fixed as redis.