Redis

Frequently used Redis commands for managing data structures, persistence, and server administration.

Key Operations

SET key value           # Set a key
GET key                 # Get a value
DEL key [key ...]       # Delete one or more keys
EXISTS key              # Check if key exists (1=yes, 0=no)
EXPIRE key seconds      # Set TTL on a key
TTL key                 # Get remaining TTL
KEYS pattern            # Find keys matching pattern (use SCAN in production)
SCAN 0 MATCH prefix:*   # Iterate keys safely

Strings

SET counter 0
INCR counter
INCRBY counter 5
APPEND key value

Lists

LPUSH mylist value      # Push to head
RPUSH mylist value      # Push to tail
LPOP mylist             # Pop from head
LRANGE mylist 0 -1      # Get all elements
BLPOP mylist timeout    # Blocking pop

Hashes

HSET user:1 name "Ravi" email "r@example.com"
HGET user:1 name
HGETALL user:1
HDEL user:1 email

Sets

SADD myset member1 member2
SMEMBERS myset
SISMEMBER myset member1
SREM myset member1

Server

INFO                    # Server statistics
DBSIZE                  # Number of keys in current DB
SELECT 1                # Switch to database 1
BGSAVE                  # Trigger background save
SHUTDOWN SAVE           # Save and shut down
FLUSHDB                 # Delete all keys in current DB
FLUSHALL                # Delete all keys in all DBs

Use FLUSHDB to clear the current Redis database, or FLUSHALL to clear all databases.

Check Redis Version

redis-server --version

Flush the Current (Default) Database

redis-cli FLUSHDB

Flush a Specific Database by Number

# Flush database number 8
redis-cli -n 8 FLUSHDB

Flush ALL Databases

redis-cli FLUSHALL

Async Flush (Redis 4.0+, non-blocking)

redis-cli FLUSHALL ASYNC

Notes

• These operations are irreversible. Always confirm you are targeting the correct database.
• In production, consider enabling RDB or AOF persistence before flushing to allow recovery.

Install Redis from the EPEL repository on Amazon Linux or CentOS and configure it as a system service.

Option 1 - Install from EPEL (Recommended)

# Amazon Linux 2 / CentOS 7
sudo amazon-linux-extras install redis6 -y
# or
sudo yum install -y redis

Option 2 - Compile from Source

sudo yum install -y gcc make
wget http://download.redis.io/redis-stable.tar.gz
tar xvzf redis-stable.tar.gz
cd redis-stable
make
sudo make install

Start and Enable Redis

sudo systemctl start redis
sudo systemctl enable redis

Basic Security Config

Edit /etc/redis/redis.conf:

bind 127.0.0.1          # Only listen locally
requirepass StrongPass  # Set a password
protected-mode yes

sudo systemctl restart redis

Verify

redis-cli ping   # Should return PONG

Remove Redis from Ubuntu, whether it was installed via apt or compiled from source.

If Installed via apt

# Remove Redis and auto-remove unused dependencies
sudo apt-get purge --auto-remove redis-server redis-tools

If Installed from Source (make install)

Source builds do not have an uninstall target. Remove the files manually:

# Stop the service
sudo systemctl stop redis
sudo systemctl disable redis

# Remove binaries (installed to /usr/local/bin by default)
sudo rm -f /usr/local/bin/redis-server
sudo rm -f /usr/local/bin/redis-cli
sudo rm -f /usr/local/bin/redis-benchmark

# Remove config and data
sudo rm -rf /etc/redis
sudo rm -f /var/lib/redis/dump.rdb

# Remove the systemd service file
sudo rm -f /etc/systemd/system/redis.service
sudo systemctl daemon-reload

Verify Removal

which redis-server   # Should return nothing
redis-cli ping       # Should fail (command not found)

Configure Magento to use Redis for the cache backend and session storage, replacing the default file-based cache for better performance and scalability.

Prerequisites

• Redis installed and running (same or separate server)
• Magento 2.x
• predis/predis or phpredis extension installed

Configure Cache Backend

Run the Magento CLI command:

php bin/magento setup:config:set \
    --cache-backend=redis \
    --cache-backend-redis-server=127.0.0.1 \
    --cache-backend-redis-db=0 \
    --cache-backend-redis-port=6379

Configure Session Storage

php bin/magento setup:config:set \
    --session-save=redis \
    --session-save-redis-host=127.0.0.1 \
    --session-save-redis-port=6379 \
    --session-save-redis-db=2 \
    --session-save-redis-max-concurrency=20

Verify Configuration

Check app/etc/env.php to confirm the Redis settings were saved. Then flush cache and test:

php bin/magento cache:flush
redis-cli -n 0 DBSIZE   # Should show cache keys

Back up Redis data using RDB snapshots and restore them on the same or a different server.

Step 1 - Find the Data Directory

redis-cli CONFIG GET dir
redis-cli CONFIG GET dbfilename

The dump file is typically /var/lib/redis/dump.rdb.

Step 2 - Create a Fresh Backup

# Trigger a synchronous save
redis-cli BGSAVE

# Wait for it to complete
redis-cli LASTSAVE   # returns Unix timestamp of last save

Step 3 - Copy the Dump File

sudo cp /var/lib/redis/dump.rdb /backup/redis-dump-$(date +%Y%m%d).rdb

Restore on the Same or Another Server

1. Stop Redis: sudo systemctl stop redis
2. Copy the dump: sudo cp /backup/redis-dump.rdb /var/lib/redis/dump.rdb
3. Fix permissions: sudo chown redis:redis /var/lib/redis/dump.rdb
4. Start Redis: sudo systemctl start redis

Automate with Cron

# Daily backup at 2 AM
0 2 * * * redis-cli BGSAVE && cp /var/lib/redis/dump.rdb /backup/redis-$(date +\%Y\%m\%d).rdb

Notes

• The restore server must run a Redis version equal to or newer than the source.

By default, Redis only listens on 127.0.0.1:6379. To allow remote connections, update the Redis config and open the firewall port.

Step 1 - Configure Redis to Listen Remotely

Edit /etc/redis/redis.conf:

# Change from:
bind 127.0.0.1

# To (specify your server IP or 0.0.0.0 for all interfaces):
bind 0.0.0.0

# Always set a password when enabling remote access:
requirepass YourStrongPassword

sudo systemctl restart redis

Step 2 - Open Firewall Port

# UFW
sudo ufw allow from CLIENT_IP to any port 6379

# iptables
sudo iptables -A INPUT -s CLIENT_IP -p tcp --dport 6379 -j ACCEPT

Verify

# Check Redis is listening
ss -tlnp | grep 6379

# Test remote connection
redis-cli -h SERVER_IP -p 6379 -a YourStrongPassword ping

Notes

• Never expose Redis to the public internet without authentication and strict firewall rules. Unauthenticated Redis instances are a common attack target.

Delete keys from a Redis database using the FLUSHDB or FLUSHALL commands.

Commands

# Delete all keys in the currently selected database
redis-cli FLUSHDB

# Delete all keys in ALL databases
redis-cli FLUSHALL

# Non-blocking flush (Redis 4.0+, runs in background)
redis-cli FLUSHALL ASYNC

Flush a Specific Database

# Select database 1 and flush it
redis-cli -n 1 FLUSHDB

Delete Keys Matching a Pattern (Safer)

# Use SCAN + DEL instead of KEYS in production
redis-cli --scan --pattern "cache:*" | xargs redis-cli DEL

Notes

• FLUSHDB/FLUSHALL are irreversible. Ensure RDB/AOF persistence is configured before running them in production.
• Prefer pattern-based deletion over full flush when only specific keys need to be removed.

Migrate a Redis database to a new server by copying the RDB dump file.

Step 1 - Save the Dump on Server A

redis-cli CONFIG GET dir    # Find the data directory (e.g. /var/lib/redis)
redis-cli SAVE             # Force synchronous save

Step 2 - Copy dump.rdb to Server B

scp /var/lib/redis/dump.rdb user@SERVER_B:/tmp/dump.rdb

Step 3 - Restore on Server B

sudo systemctl stop redis
sudo cp /tmp/dump.rdb /var/lib/redis/dump.rdb
sudo chown redis:redis /var/lib/redis/dump.rdb
sudo systemctl start redis

Verify

redis-cli DBSIZE    # Should match the original server key count
redis-cli KEYS "*" | head -20

Alternative - Use redis-cli --pipe or MIGRATE Command

# Migrate a single key from A to B
redis-cli MIGRATE SERVER_B_IP 6379 mykey 0 5000

Notes

• Server B must run the same or a newer version of Redis as Server A.
• For live migration with minimal downtime, consider setting up replication temporarily.