Configuration

Redis configuration options and redis.conf management

Overview

Redis configuration can be managed through the redis.conf file or dynamically at runtime using the CONFIG command. This guide covers configuration directives, runtime management, and best practices.

Configuration File

Starting Redis with a Configuration File

Redis must be started with the configuration file path as the first argument:

./redis-server /path/to/redis.conf

Unit Specifications

Redis supports convenient memory size units (case insensitive):

• 1k => 1000 bytes
• 1kb => 1024 bytes
• 1m => 1000000 bytes
• 1mb => 1024*1024 bytes
• 1g => 1000000000 bytes
• 1gb => 102410241024 bytes

CONFIG Commands

CONFIG GET

Retrieve the value of configuration parameters.

# Get a specific configuration
CONFIG GET maxmemory

# Get multiple configurations
CONFIG GET maxmemory maxmemory-policy

# Use glob patterns
CONFIG GET max*
CONFIG GET *memory*

The command returns a map of configuration names to values.

CONFIG SET

Change configuration parameters at runtime without restarting Redis.

# Set a single parameter
CONFIG SET maxmemory 2gb

# Set multiple parameters
CONFIG SET maxmemory 2gb maxmemory-policy allkeys-lru

Some configuration directives are immutable and cannot be changed at runtime. Others are protected and require special permissions. Changing configuration at runtime does not persist across restarts unless you use CONFIG REWRITE.

CONFIG REWRITE

Persist runtime configuration changes back to the redis.conf file:

CONFIG REWRITE

This command rewrites the configuration file, preserving comments and structure while updating changed values.

Core Configuration Directives

Network Configuration

bind

Specify which network interfaces Redis should listen on:

# Listen on localhost only (default, secure)
bind 127.0.0.1 -::1

# Listen on specific IP addresses
bind 192.168.1.100 10.0.0.1

# Listen on all interfaces (NOT recommended for production)
bind * -::*

port

Set the TCP port (default: 6379):

port 6379

# Disable TCP socket
port 0

tcp-backlog

Set the TCP listen() backlog for high-traffic environments:

tcp-backlog 511

On Linux, ensure /proc/sys/net/core/somaxconn and tcp_max_syn_backlog are set appropriately.

tcp-keepalive

Send TCP keepalive messages to detect dead peers:

# Send ACKs every 300 seconds
tcp-keepalive 300

timeout

Close idle client connections after N seconds (0 to disable):

# Close connections idle for 300 seconds
timeout 300

# Never close idle connections
timeout 0

General Configuration

daemonize

Run Redis as a daemon:

daemonize yes

pidfile

Specify the PID file location:

pidfile /var/run/redis_6379.pid

loglevel

Set the server verbosity level:

# Options: debug, verbose, notice, warning, nothing
loglevel notice

logfile

Specify the log file path:

# Log to file
logfile /var/log/redis/redis-server.log

# Log to stdout
logfile ""

databases

Set the number of databases:

# Default is 16 databases (0-15)
databases 16

Snapshotting Configuration

save

Configure automatic RDB snapshots:

# Save after 3600 seconds if at least 1 key changed
# Save after 300 seconds if at least 100 keys changed
# Save after 60 seconds if at least 10000 keys changed
save 3600 1 300 100 60 10000

# Disable snapshotting
save ""

stop-writes-on-bgsave-error

Stop accepting writes if background save fails:

stop-writes-on-bgsave-error yes

rdbcompression

Compress RDB files using LZF:

rdbcompression yes

rdbchecksum

Add CRC64 checksum to RDB files:

rdbchecksum yes

dbfilename

Set the RDB filename:

dbfilename dump.rdb

dir

Set the working directory for RDB and AOF files:

dir ./

Memory Management

maxmemory

Set a memory usage limit:

# Set 2GB limit
maxmemory 2gb

# No limit (default)
# maxmemory 0

When using replicas, set maxmemory lower than available RAM to account for replica output buffers.

maxmemory-policy

Define eviction policy when maxmemory is reached:

# Available policies:
# volatile-lru - Evict using LRU, only keys with expire set
# allkeys-lru - Evict any key using LRU
# volatile-lfu - Evict using LFU, only keys with expire set
# allkeys-lfu - Evict any key using LFU
# volatile-lrm - Evict using LRM, only keys with expire set
# allkeys-lrm - Evict any key using LRM
# volatile-random - Remove random key with expire set
# allkeys-random - Remove random key
# volatile-ttl - Remove key with nearest expire time
# noeviction - Return errors on write operations (default)

maxmemory-policy noeviction

LRU vs LRM:

• LRU (Least Recently Used): Updates timestamp on both read and write operations
• LRM (Least Recently Modified): Updates timestamp only on write operations
• LFU (Least Frequently Used): Tracks access frequency

maxmemory-samples

Number of keys to sample for eviction algorithms:

# Default is 5, higher is more accurate but slower
maxmemory-samples 5

Client Configuration

maxclients

Maximum number of simultaneous client connections:

maxclients 10000

In Redis Cluster, each node uses two connections (incoming and outgoing), so size accordingly.

Module Loading

Load Redis modules at startup:

loadmodule /path/to/my_module.so
loadmodule /path/to/other_module.so
loadmodule /path/to/module.so arg1 arg2 arg3

Including Configuration Files

Include additional configuration files:

# Include single file
include /path/to/local.conf

# Include with wildcards
include /path/to/fragments/*.conf

Include directives at the beginning of the file for base configuration, or at the end to override settings.

Configuration Management Best Practices

1. Use Version Control
2. Store your redis.conf in version control to track changes and enable rollback.
3. Test Configuration Changes
4. Before applying to production:
5. # Test configuration file syntax
   redis-server /path/to/redis.conf --test-memory 1
   
   # Use CONFIG SET to test changes before persisting
   CONFIG SET maxmemory 2gb
   # Verify behavior, then:
   CONFIG REWRITE
   

6. Monitor Configuration
7. Regularly audit your configuration:
8. # Get all configuration
   CONFIG GET *
   
   # Check specific security settings
   CONFIG GET bind
   CONFIG GET protected-mode
   CONFIG GET requirepass
   

9. Document Custom Settings
10. Add comments explaining why specific values were chosen:
11. # Increased maxclients for high-traffic application
    # Based on load testing results from 2024-01-15
    maxclients 50000
    

Runtime Configuration Examples

Example: Adjust Memory Settings

# Check current memory usage
INFO memory

# Set memory limit and eviction policy
CONFIG SET maxmemory 4gb
CONFIG SET maxmemory-policy allkeys-lru

# Persist changes
CONFIG REWRITE

Example: Enable Logging

# Change log level for debugging
CONFIG SET loglevel debug

# Change log file location
CONFIG SET logfile /var/log/redis/debug.log

# Revert after debugging
CONFIG SET loglevel notice

Example: Adjust Snapshot Frequency

# More frequent snapshots for critical data
CONFIG SET save "900 1 300 10 60 10000"

# Persist configuration
CONFIG REWRITE

Configuration Reset

Reset specific configuration parameters to their default values by using CONFIG SET with appropriate values, or edit redis.conf and restart Redis.

See Also

• Security Configuration
• Monitoring
• Performance Tuning
• TLS Configuration