Port 6379: Redis

What is Port 6379?

Port 6379 is the default port for Redis, an open-source in-memory data structure store. Redis is commonly used for caching, session storage, message queuing, and real-time analytics.

Connection Examples

# redis-cli
redis-cli -h localhost -p 6379
redis-cli -h localhost -p 6379 -a password

# Connection URL
redis://localhost:6379
redis://:password@localhost:6379/0
rediss://localhost:6379  # TLS

# Node.js (ioredis)
const Redis = require('ioredis');
const redis = new Redis({
  host: 'localhost',
  port: 6379,
  password: 'secret'
});

# Python
import redis
r = redis.Redis(host='localhost', port=6379, password='secret')

Security Configuration

# /etc/redis/redis.conf

# Bind to localhost only (safe default)
bind 127.0.0.1 ::1

# Set a strong password
requirepass your_strong_password_here

# Disable dangerous commands
rename-command FLUSHDB ""
rename-command FLUSHALL ""
rename-command DEBUG ""
rename-command CONFIG ""

# Restart Redis
sudo systemctl restart redis

Common Use Cases

• Caching: Store frequently accessed data in memory
• Session storage: Store user sessions for web apps
• Rate limiting: Track request counts with TTL
• Message queue: Pub/Sub for real-time messaging
• Leaderboards: Sorted sets for rankings

Basic Commands

# Test connection
redis-cli ping
# Response: PONG

# Set and get values
SET mykey "Hello"
GET mykey

# Set with expiration (seconds)
SETEX session:123 3600 "user_data"

# Check TTL
TTL session:123

# List all keys (use carefully in production)
KEYS *

# Get server info
INFO

Troubleshooting

# Check if Redis is running
sudo systemctl status redis
sudo ss -tlnp | grep 6379

# Test connection
redis-cli ping
redis-cli -a password ping

# Check what Redis is bound to
redis-cli CONFIG GET bind

# Monitor commands in real-time
redis-cli monitor

# Check memory usage
redis-cli INFO memory

Common Issues

• NOAUTH: Authentication required - provide password
• Connection refused: Redis not running or wrong bind address
• OOM: Out of memory - increase maxmemory or eviction policy
• Slow operations: Check for blocking commands with SLOWLOG

How to Check if Port 6379 is Open

Verify Redis connectivity with these commands.

# Quick health check
redis-cli ping                     # PONG = healthy
redis-cli -a password ping         # With auth

# Check if Redis is listening
sudo ss -tlnp | grep 6379
sudo lsof -i :6379

# From a remote machine
nc -zv redis-server.example.com 6379
nmap -p 6379 redis-server.example.com

# Check bind address and config
redis-cli CONFIG GET bind
redis-cli CONFIG GET requirepass
redis-cli INFO server | grep tcp_port

Redis Memory Management

Redis stores data in memory, so proper memory configuration is critical to avoid OOM (Out of Memory) errors.

# /etc/redis/redis.conf

# Set maximum memory limit
maxmemory 256mb

# Eviction policy when maxmemory is reached
maxmemory-policy allkeys-lru    # Evict least recently used keys
# Other options: volatile-lru, allkeys-random, noeviction

# Check memory usage
redis-cli INFO memory
redis-cli MEMORY USAGE mykey

# Find biggest keys
redis-cli --bigkeys

Monitoring Redis with UptimeSignal

Redis downtime on port 6379 can cause session loss, cache misses that overload your database, and broken real-time features. UptimeSignal monitors your application endpoints to detect when Redis issues start impacting users. Combine with checks on PostgreSQL (port 5432) and MySQL (port 3306) for complete data layer visibility.

Frequently Asked Questions