Set up Redis Sentinel to monitor Redis master-replica deployments and automatically handle failover scenarios. This tutorial covers configuring a 3-node Sentinel cluster with quorum-based decision making for production-grade high availability.

Prerequisites

At least 3 servers for proper quorum
Network connectivity between all nodes
Basic understanding of Redis replication

What this solves

Redis Sentinel provides high availability for Redis deployments by monitoring master and replica instances, detecting failures, and automatically promoting replicas to master when needed. This eliminates single points of failure and ensures your Redis service remains available during hardware or network issues.

Step-by-step configuration

Update system packages

Start by updating your package manager to ensure you get the latest Redis packages.

sudo apt update && sudo apt upgrade -y

sudo dnf update -y

Install Redis server

Install Redis on all nodes that will participate in the Sentinel cluster. You'll need Redis installed even on Sentinel-only nodes.

sudo apt install -y redis-server redis-sentinel

sudo dnf install -y redis redis-sentinel epel-release

Configure Redis master instance

Configure the primary Redis instance that will initially serve as master. Set up authentication and bind to the appropriate network interface.

# Network and security
bind 0.0.0.0
protected-mode yes
port 6379
requirepass StrongMasterPass123
masterauth StrongMasterPass123

Persistence
save 900 1
save 300 10
save 60 10000
rdbcompression yes
rdbchecksum yes
dbfilename dump.rdb
dir /var/lib/redis

Logging
loglevel notice
logfile /var/log/redis/redis-server.log
syslog-enabled yes
syslog-ident redis

Memory management
maxmemory-policy allkeys-lru
tcp-keepalive 300

Configure Redis replica instances

Set up replica instances on separate servers. These will automatically sync with the master and can be promoted during failover.

# Network and security
bind 0.0.0.0
protected-mode yes
port 6379
requirepass StrongReplicaPass123
masterauth StrongMasterPass123

Replication configuration
replicaof 203.0.113.10 6379
replica-read-only yes
replica-serve-stale-data yes
replica-priority 100

Persistence
save 900 1
save 300 10
save 60 10000
rdbcompression yes
rdbchecksum yes
dbfilename dump.rdb
dir /var/lib/redis

Logging
loglevel notice
logfile /var/log/redis/redis-server.log
syslog-enabled yes
syslog-ident redis

Memory management
maxmemory-policy allkeys-lru
tcp-keepalive 300

Set correct Redis file permissions

Ensure Redis can read its configuration and write to data directories with proper ownership and minimal permissions.

sudo chown redis:redis /etc/redis/redis.conf
sudo chmod 640 /etc/redis/redis.conf
sudo chown -R redis:redis /var/lib/redis
sudo chmod 755 /var/lib/redis
sudo chown redis:redis /var/log/redis
sudo chmod 755 /var/log/redis

Never use chmod 777. It gives every user on the system full access to your Redis files. Instead, use proper ownership with chown and minimal permissions as shown above.

Configure Redis Sentinel on first node

Set up the first Sentinel instance with monitoring configuration and quorum settings. The quorum determines how many Sentinels must agree before initiating failover.

# Basic Sentinel configuration
port 26379
bind 0.0.0.0
protected-mode no
sentinel deny-scripts-reconfig yes

Monitor master instance
sentinel monitor mymaster 203.0.113.10 6379 2
sentinel auth-pass mymaster StrongMasterPass123
sentinel down-after-milliseconds mymaster 5000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 30000

Logging
logfile /var/log/redis/sentinel.log
loglevel notice
syslog-enabled yes
syslog-ident sentinel

Working directory
dir /var/lib/redis/sentinel

Configure additional Sentinel nodes

Deploy identical Sentinel configurations on at least two more servers for redundancy. Use the same master IP but different Sentinel IDs.

# Basic Sentinel configuration
port 26379
bind 0.0.0.0
protected-mode no
sentinel deny-scripts-reconfig yes

Monitor master instance (same as other Sentinels)
sentinel monitor mymaster 203.0.113.10 6379 2
sentinel auth-pass mymaster StrongMasterPass123
sentinel down-after-milliseconds mymaster 5000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 30000

Logging
logfile /var/log/redis/sentinel.log
loglevel notice
syslog-enabled yes
syslog-ident sentinel

Working directory
dir /var/lib/redis/sentinel

Create Sentinel working directory

Create the directory where Sentinel stores its runtime state and ensure proper permissions.

sudo mkdir -p /var/lib/redis/sentinel
sudo chown redis:redis /var/lib/redis/sentinel
sudo chmod 755 /var/lib/redis/sentinel
sudo chown redis:redis /etc/redis/sentinel.conf
sudo chmod 640 /etc/redis/sentinel.conf

Configure firewall rules

Open the necessary ports for Redis and Sentinel communication between cluster nodes.

sudo ufw allow from 203.0.113.0/24 to any port 6379 comment 'Redis'
sudo ufw allow from 203.0.113.0/24 to any port 26379 comment 'Redis Sentinel'
sudo ufw reload

sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="203.0.113.0/24" port protocol="tcp" port="6379" accept'
sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="203.0.113.0/24" port protocol="tcp" port="26379" accept'
sudo firewall-cmd --reload

Start Redis master and replica services

Enable and start Redis on the master and replica nodes first, then verify replication is working.

sudo systemctl enable --now redis-server
sudo systemctl status redis-server

Start Redis Sentinel services

Start Sentinel on all three nodes after Redis instances are running and replication is established.

sudo systemctl enable --now redis-sentinel
sudo systemctl status redis-sentinel

Test automatic failover

Simulate master failure by stopping the Redis master service and observe Sentinel promoting a replica.

# On master node, stop Redis to simulate failure
sudo systemctl stop redis-server

Monitor Sentinel logs during failover
sudo tail -f /var/log/redis/sentinel.log

Check which instance is now master
redis-cli -p 26379 sentinel masters

Verify your setup

Check that Sentinel is monitoring your Redis instances and can detect the current master.

# Check Sentinel status
redis-cli -p 26379 sentinel masters
redis-cli -p 26379 sentinel slaves mymaster
redis-cli -p 26379 sentinel sentinels mymaster

Verify Redis replication
redis-cli -h 203.0.113.10 -a StrongMasterPass123 info replication

Test failover capabilities
redis-cli -p 26379 sentinel failover mymaster

Common issues

Symptom	Cause	Fix
Sentinel can't connect to master	Firewall blocking ports or wrong IP	Check firewall rules and master bind address
Authentication failures	Mismatched passwords in config	Verify requirepass and masterauth match
Failover doesn't trigger	Insufficient Sentinels or wrong quorum	Check at least 3 Sentinels running with quorum=2
Permission denied errors	Wrong file ownership or permissions	`sudo chown redis:redis /etc/redis/* && chmod 640`
Split-brain scenarios	Network partitions with even Sentinel count	Always use odd number of Sentinels (3, 5, 7)

Next steps

Automated install script

Run this to automate the entire setup

install.sh

#!/usr/bin/env bash

set -euo pipefail

# Colors for output
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
BLUE='\033[0;34m'
NC='\033[0m' # No Color

# Default values
MASTER_IP=""
NODE_TYPE=""
MASTER_PASSWORD="StrongMasterPass123"
REPLICA_PASSWORD="StrongReplicaPass123"

# Usage function
usage() {
    echo "Usage: $0 <master|replica|sentinel> <master_ip> [options]"
    echo "Options:"
    echo "  --master-password PASSWORD    Set master password (default: StrongMasterPass123)"
    echo "  --replica-password PASSWORD   Set replica password (default: StrongReplicaPass123)"
    echo "Examples:"
    echo "  $0 master 203.0.113.10"
    echo "  $0 replica 203.0.113.10"
    echo "  $0 sentinel 203.0.113.10"
    exit 1
}

# Parse arguments
if [[ $# -lt 2 ]]; then
    usage
fi

NODE_TYPE="$1"
MASTER_IP="$2"
shift 2

while [[ $# -gt 0 ]]; do
    case $1 in
        --master-password)
            MASTER_PASSWORD="$2"
            shift 2
            ;;
        --replica-password)
            REPLICA_PASSWORD="$2"
            shift 2
            ;;
        *)
            echo -e "${RED}Unknown option: $1${NC}"
            usage
            ;;
    esac
done

# Validate node type
if [[ ! "$NODE_TYPE" =~ ^(master|replica|sentinel)$ ]]; then
    echo -e "${RED}Error: Invalid node type. Must be master, replica, or sentinel${NC}"
    usage
fi

# Detect distribution
if [ -f /etc/os-release ]; then
    . /etc/os-release
    case "$ID" in
        ubuntu|debian) 
            PKG_MGR="apt"
            PKG_UPDATE="apt update && apt upgrade -y"
            PKG_INSTALL="apt install -y"
            REDIS_CONF="/etc/redis/redis.conf"
            SENTINEL_CONF="/etc/redis/sentinel.conf"
            REDIS_SERVICE="redis-server"
            SENTINEL_SERVICE="redis-sentinel"
            ;;
        almalinux|rocky|centos|rhel|ol|fedora) 
            PKG_MGR="dnf"
            PKG_UPDATE="dnf update -y"
            PKG_INSTALL="dnf install -y"
            REDIS_CONF="/etc/redis/redis.conf"
            SENTINEL_CONF="/etc/redis-sentinel.conf"
            REDIS_SERVICE="redis"
            SENTINEL_SERVICE="redis-sentinel"
            ;;
        amzn) 
            PKG_MGR="yum"
            PKG_UPDATE="yum update -y"
            PKG_INSTALL="yum install -y"
            REDIS_CONF="/etc/redis/redis.conf"
            SENTINEL_CONF="/etc/redis-sentinel.conf"
            REDIS_SERVICE="redis"
            SENTINEL_SERVICE="redis-sentinel"
            ;;
        *) 
            echo -e "${RED}Error: Unsupported distribution: $ID${NC}"
            exit 1 
            ;;
    esac
else
    echo -e "${RED}Error: Cannot detect distribution${NC}"
    exit 1
fi

# Cleanup function for rollback
cleanup() {
    echo -e "${RED}Error occurred. Cleaning up...${NC}"
    systemctl stop $REDIS_SERVICE 2>/dev/null || true
    systemctl stop $SENTINEL_SERVICE 2>/dev/null || true
}

trap cleanup ERR

# Check prerequisites
echo -e "${BLUE}[1/8] Checking prerequisites...${NC}"
if [[ $EUID -ne 0 ]]; then
    echo -e "${RED}Error: This script must be run as root${NC}"
    exit 1
fi

# Update system packages
echo -e "${BLUE}[2/8] Updating system packages...${NC}"
eval $PKG_UPDATE

# Install Redis and dependencies
echo -e "${BLUE}[3/8] Installing Redis packages...${NC}"
if [[ "$ID" =~ ^(ubuntu|debian)$ ]]; then
    $PKG_INSTALL redis-server redis-sentinel
elif [[ "$ID" =~ ^(almalinux|rocky|centos|rhel|ol|fedora|amzn)$ ]]; then
    if [[ "$ID" != "fedora" ]]; then
        $PKG_INSTALL epel-release || true
    fi
    $PKG_INSTALL redis redis-sentinel
fi

# Create necessary directories
echo -e "${BLUE}[4/8] Creating directories and setting permissions...${NC}"
mkdir -p /var/lib/redis/sentinel
mkdir -p /var/log/redis
chown -R redis:redis /var/lib/redis
chmod 755 /var/lib/redis /var/lib/redis/sentinel
chown redis:redis /var/log/redis
chmod 755 /var/log/redis

# Configure Redis based on node type
echo -e "${BLUE}[5/8] Configuring Redis for $NODE_TYPE node...${NC}"

if [[ "$NODE_TYPE" == "master" || "$NODE_TYPE" == "replica" ]]; then
    cat > "$REDIS_CONF" << EOF
# Network and security
bind 0.0.0.0
protected-mode yes
port 6379
requirepass $([[ "$NODE_TYPE" == "master" ]] && echo "$MASTER_PASSWORD" || echo "$REPLICA_PASSWORD")
masterauth $MASTER_PASSWORD

EOF

    if [[ "$NODE_TYPE" == "replica" ]]; then
        cat >> "$REDIS_CONF" << EOF
# Replication configuration
replicaof $MASTER_IP 6379
replica-read-only yes
replica-serve-stale-data yes
replica-priority 100

EOF
    fi

    cat >> "$REDIS_CONF" << EOF
# Persistence
save 900 1
save 300 10
save 60 10000
rdbcompression yes
rdbchecksum yes
dbfilename dump.rdb
dir /var/lib/redis

# Logging
loglevel notice
logfile /var/log/redis/redis-server.log
syslog-enabled yes
syslog-ident redis

# Memory management
maxmemory-policy allkeys-lru
tcp-keepalive 300
EOF

    chown redis:redis "$REDIS_CONF"
    chmod 640 "$REDIS_CONF"
fi

# Configure Sentinel
if [[ "$NODE_TYPE" == "sentinel" || "$NODE_TYPE" == "master" || "$NODE_TYPE" == "replica" ]]; then
    echo -e "${BLUE}[6/8] Configuring Redis Sentinel...${NC}"
    
    cat > "$SENTINEL_CONF" << EOF
# Basic Sentinel configuration
port 26379
bind 0.0.0.0
protected-mode no
sentinel deny-scripts-reconfig yes

# Monitor master instance
sentinel monitor mymaster $MASTER_IP 6379 2
sentinel auth-pass mymaster $MASTER_PASSWORD
sentinel down-after-milliseconds mymaster 5000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 30000

# Logging
logfile /var/log/redis/sentinel.log
loglevel notice
syslog-enabled yes
syslog-ident sentinel

# Working directory
dir /var/lib/redis/sentinel
EOF

    chown redis:redis "$SENTINEL_CONF"
    chmod 640 "$SENTINEL_CONF"
fi

# Configure firewall
echo -e "${BLUE}[7/8] Configuring firewall...${NC}"
if command -v firewall-cmd >/dev/null 2>&1 && systemctl is-active --quiet firewalld; then
    if [[ "$NODE_TYPE" == "master" || "$NODE_TYPE" == "replica" ]]; then
        firewall-cmd --permanent --add-port=6379/tcp
    fi
    firewall-cmd --permanent --add-port=26379/tcp
    firewall-cmd --reload
elif command -v ufw >/dev/null 2>&1; then
    if [[ "$NODE_TYPE" == "master" || "$NODE_TYPE" == "replica" ]]; then
        ufw allow 6379/tcp
    fi
    ufw allow 26379/tcp
fi

# Start and enable services
echo -e "${BLUE}[8/8] Starting and enabling services...${NC}"
if [[ "$NODE_TYPE" == "master" || "$NODE_TYPE" == "replica" ]]; then
    systemctl enable $REDIS_SERVICE
    systemctl restart $REDIS_SERVICE
fi

systemctl enable $SENTINEL_SERVICE
systemctl restart $SENTINEL_SERVICE

# Verification checks
echo -e "${YELLOW}Performing verification checks...${NC}"
sleep 3

if [[ "$NODE_TYPE" == "master" || "$NODE_TYPE" == "replica" ]]; then
    if systemctl is-active --quiet $REDIS_SERVICE; then
        echo -e "${GREEN}✓ Redis service is running${NC}"
    else
        echo -e "${RED}✗ Redis service failed to start${NC}"
        exit 1
    fi
fi

if systemctl is-active --quiet $SENTINEL_SERVICE; then
    echo -e "${GREEN}✓ Redis Sentinel service is running${NC}"
else
    echo -e "${RED}✗ Redis Sentinel service failed to start${NC}"
    exit 1
fi

# Test connectivity
if [[ "$NODE_TYPE" == "master" || "$NODE_TYPE" == "replica" ]]; then
    if redis-cli -p 6379 -a "$([[ "$NODE_TYPE" == "master" ]] && echo "$MASTER_PASSWORD" || echo "$REPLICA_PASSWORD")" ping 2>/dev/null | grep -q PONG; then
        echo -e "${GREEN}✓ Redis connectivity test passed${NC}"
    else
        echo -e "${YELLOW}⚠ Redis connectivity test failed (may need manual verification)${NC}"
    fi
fi

echo -e "${GREEN}Redis $NODE_TYPE node installation and configuration completed successfully!${NC}"
echo -e "${YELLOW}Configuration files:${NC}"
if [[ "$NODE_TYPE" == "master" || "$NODE_TYPE" == "replica" ]]; then
    echo -e "  Redis: $REDIS_CONF"
fi
echo -e "  Sentinel: $SENTINEL_CONF"
echo -e "${YELLOW}Log files:${NC}"
echo -e "  Redis: /var/log/redis/redis-server.log"
echo -e "  Sentinel: /var/log/redis/sentinel.log"

Review the script before running. Execute with: bash install.sh

#redis #sentinel #high-availability #failover #clustering

Configure Redis Sentinel for high availability and automatic failover

Prerequisites

What this solves

Step-by-step configuration

Update system packages

Install Redis server

Configure Redis master instance

Persistence

Logging

Memory management

Configure Redis replica instances

Replication configuration

Persistence

Logging

Memory management

Set correct Redis file permissions

Configure Redis Sentinel on first node

Monitor master instance

Logging

Working directory

Configure additional Sentinel nodes

Monitor master instance (same as other Sentinels)

Logging

Working directory

Create Sentinel working directory

Configure firewall rules

Start Redis master and replica services

Start Redis Sentinel services

Test automatic failover

Monitor Sentinel logs during failover

Check which instance is now master

Verify your setup

Verify Redis replication

Test failover capabilities

Common issues

Next steps

Related tutorials

Configure TimescaleDB continuous aggregates for real-time analytics with PostgreSQL optimization

Configure ZooKeeper for ClickHouse replication with multi-node cluster setup

Install and configure TimescaleDB with PostgreSQL for high-performance time-series data

Don't want to manage this yourself?