How to install and configure Redis on CentOS 7

Redis is an in-memory data structure store that is commonly used as a database, cache or a message broker. What makes Redis powerful is its optional ability to have data persistence. Therefore your dataset isn’t lost during restarts of the service.

The article below will discuss how to install, configure and provide basic security for Redis. From there, it will go into the basic use cases I use it for on a daily basis, session storing and general caching.

Installation

[[email protected] ~]# yum install epel-release
[[email protected] ~]# yum install redis
[[email protected] ~]# systemctl enable redis
[[email protected] ~]# systemctl start redis.service
[[email protected] ~]# redis-cli ping

Configuration

Redis listens on port 6379 by default and needs some additional configuration to ensure that it is secured. If you do not protect Redis with a firewall, authentication and have it listen only on a private network, there is a extremely high risk of leaking sensitive data.

First, set Redis to only listen on your private network. Redis does not have any type of encryption built in, it is important that the data is transferred only over private networks or secured tunnels. Set Redis to listen on the private interface by:

[[email protected] ~]# vim /etc/redis.conf
...
bind redis_servers_private_IP
...

If Redis is being installed on a stand alone web server and will not need to accept connections from other clients, then you can set Redis to listen on the local socket instead by commenting out the bind value and setting up a socket by:

[[email protected] ~]# mkdir /var/run/redis
[[email protected] ~]# chown redis:redis /var/run/redis
[[email protected] ~]# vim /etc/redis.conf
...
# bind 127.0.0.1
unixsocket /var/run/redis/redis.sock
unixsocketperm 777

If you do not have a dedicated firewall, use your OS’s built in firewall to only allow in connections from trusted web servers using their internal IP’s. Some quick examples are below:

# iptables
[[email protected] ~]# vim /etc/sysconfig/iptables
...
-A INPUT -p tcp -m tcp --dport 6379 -s client_server_private_IP -m comment --comment "redis" -j ACCEPT
[[email protected] ~]# service iptables restart

# firewalld
[[email protected] ~]# firewall-cmd --permanent --new-zone=redis
[[email protected] ~]# firewall-cmd --permanent --zone=redis --add-port=6379/tcp
[[email protected] ~]# firewall-cmd --permanent --zone=redis --add-source=client_server_private_IP
[[email protected] ~]# firewall-cmd --reload

To protect Redis further, setup authentication which is a built in security feature. This will force clients to authenticate before being granted access. Use a tool such as apg or pwgen to create a secure password. Set the password within Redis by:

[[email protected] ~]# vim /etc/redis.conf
...
requirepass your_secure_password_here
...

[[email protected] ~]# systemctl restart redis

Then test to ensure the password works by:

# This should fail
[[email protected] ~]# redis_cli
127.0.0.1:6379> set key1 10
(error) NOAUTH Authentication required.

# This should work
[[email protected] ~]# redis-cli
127.0.0.1:6379> auth your_secure_password_here
127.0.0.1:6379> set key1 10
OK
127.0.0.1:6379> get key1
"10"

Next, we need to secure the file permissions for Redis. The redis.conf contains the password for redis, so that file shouldn’t be readable by everyone. We also want to lock down the Redis data directory. Lock down the permissions on Redis by:

[[email protected] ~]# chown redis:redis /var/lib/redis
[[email protected] ~]# chmod 700 /var/lib/redis
[[email protected] ~]# chown redis:redis /etc/redis.conf
[[email protected] ~]# chmod 600 /etc/redis.conf
[[email protected] ~]# systemctl restart redis

The Official Redis Administration Guide recommends to disable Transparent Huge Pages (THP). This can be performed live by:

[[email protected] ~]# echo 'never' > /sys/kernel/mm/transparent_hugepage/enabled
[[email protected] ~]# echo 'never' > /sys/kernel/mm/transparent_hugepage/defrag

And disable Transparent Huge Pages (THP) at boot time by making a systemd unit file:

[[email protected] ~]# vim /etc/systemd/system/disable-thp.service
[Unit]
Description=Disable Transparent Huge Pages (THP)

[Service]
Type=simple
ExecStart=/bin/sh -c "echo 'never' > /sys/kernel/mm/transparent_hugepage/enabled && echo 'never' > /sys/kernel/mm/transparent_hugepage/defrag"

[Install]
WantedBy=multi-user.target

[[email protected] ~]# systemctl daemon-reload
[[email protected] ~]# systemctl start disable-thp
[[email protected] ~]# systemctl enable disable-thp

The Official Redis Administration Guide also recommends setting the following sysctl:

[[email protected] ~]# sysctl vm.overcommit_memory=1
[[email protected] ~]# vim /etc/sysctl.conf
...
vm.overcommit_memory = 1
...

Redis Configurations

Now that Redis is installed and secured, its time to tune it for your application’s needs. There are typically 2 types of Redis cache configurations I see:
Session store
Database cache or full page cache

The session cache allows for a single locations for your application to store sessions that would normally be stored by PHP on the local file system. It is important to ensure that the data is saved to disk so you don’t lose all the sessions between restarts of Redis. This is one of the primary advantages of using Redis over Memcached.

The full page cache is great for caching SQL queries or for serving as a full page cache for applications such as Magento or WordPress, caching images, videos, html, css or js. Generally this type of cache doesn’t need to be persistent across restarts of Redis.

Redis Configurations – Session store

When using Redis as a session store, you want to ensure that the Redis data persists between restarts of Redis. Otherwise your users could be left wondering why their shopping carts all of a sudden vanished. The example below will have disk persistence enabled with a memory limit of 1.5G (1536M).

These settings may or may not work for you! Adjust your settings to meet your environments requirements!

[[email protected] ~]# vim /etc/redis.conf
...
## Ensure disk persistence is enabled
save 900 1
save 300 10
save 60 10000
...
## Set the max memory
maxmemory 1536mb
...

[[email protected] ~]# systemctl restart redis

Redis Configurations – Database cache or full page cache

When using Redis for database caching or as a FPC for applications like WordPress or Magento, I disable disk persistence. This means the cache will only be stored in memory and lost whenever redis restart. I also set the memory limit to 1.5G (1536M) for starters and adjust accordingly from there. Since I am only storing cached data, I can avoid out of memory issues by allowing Redis to automatically remove the oldest cache entries using the maxmemory-policy allkeys-lru. Read up on the Redis supported eviction policies here.

These settings may or may not work for you! Adjust your settings to meet your environments requirements! Remember, this example assumes everything in Redis can be lost when the service restarts and the eviction policy will remove the least used keys out of all the data. I typically find this works for Magento and WordPress redis setups:

[[email protected] ~]# vim /etc/redis.conf
...
## Disable disk persistence
#save 900 1
#save 300 10
#save 60 10000
...
## Set the max memory
maxmemory 1536mb
...
## Update the eviction policy
maxmemory-policy allkeys-lru
...

[[email protected] ~]# systemctl restart redis

Multiple Redis Configurations

Redis has the ability to utilize multiple caching configurations with their own settings. The only requirement is that each instance of Redis listens on a unique port, has a unique pid, and of course has its own config and startup script. In the example below, we are going to have 2 redis instances running called redis-sessions and redis-cache. To avoid confusion, we will disable the original redis instance.

# Create 2 new configs and modify the values accordingly
[[email protected] ~]# cp /etc/redis.conf /etc/redis-session.conf
[[email protected] ~]# vim /etc/redis-session.conf
...
pidfile /var/run/redis_session.pid
port 6379
logfile /var/log/redis/redis-session.log
dir /var/lib/redis-session
...
# If unixsocket is uncommented, then update to:
unixsocket /var/run/redis/redis-session.sock
unixsocketperm 777
...

[[email protected] ~]# cp /etc/redis.conf /etc/redis-cache.conf
...
pidfile /var/run/redis_cache.pid
port 6380
logfile /var/log/redis/redis-cache.log
dir /var/lib/redis-cache
...
# If unixsocket is uncommented, then update to:
unixsocket /var/run/redis/redis-cache.sock
unixsocketperm 777
...

# Create directories and secure the permissions
[[email protected] ~]# mkdir /var/lib/redis-session /var/lib/redis-cache
[[email protected] ~]# chown redis:redis /var/lib/redis-session /var/lib/redis-cache /etc/redis-session.conf /etc/redis-cache.conf
[[email protected] ~]# chmod 700 /var/lib/redis-session /var/lib/redis-cache
[[email protected] ~]# chmod 600 /etc/redis-session.conf /etc/redis-cache.conf

# Create startup files
[[email protected] ~]# cp /usr/lib/systemd/system/redis.service /usr/lib/systemd/system/redis-session.service
[[email protected] ~]# vim /usr/lib/systemd/system/redis-session.service
...
ExecStart=/usr/bin/redis-server /etc/redis-session.conf --daemonize no
...
[[email protected] ~]# cp /usr/lib/systemd/system/redis.service /usr/lib/systemd/system/redis-cache.service
[[email protected] ~]# vim /usr/lib/systemd/system/redis-cache.service
...
ExecStart=/usr/bin/redis-server /etc/redis-cache.conf --daemonize no
...

# Stop and disable old instance, start new instances
[[email protected] ~]# systemctl daemon-reload
[[email protected] ~]# systemctl stop redis.service && systemctl disable redis.service
[[email protected] ~]# systemctl enable redis-session.service && systemctl start redis-session.service
[[email protected] ~]# systemctl enable redis-cache.service && systemctl start redis-cache.service

# Finally, edit the /etc/redis-session.conf and /etc/redis-cache.conf using the instructions earlier in this article for configuring sessions and db cache.

Client setup

The typical use cases I run into on a day to day basis are clients using Redis for their PHP application. Redis can be used to store cached content, or it can be used to centrally store sessions. Therefore these examples will be PHP focused.

Client setup – General data caching

For storing data, there is nothing that needs to be configured on the client side. The application code itself is what controls storing content within Redis.

Client setup – Storing sessions in Redis

To have Redis act as a central server for sessions, some additional configuration is needed on each client web server. Install php-memcache for your version of PHP. Assuming the default PHP version is installed from the package manager, you can install it by:

[[email protected] ~]# yum install php-pecl-redis
[[email protected] ~]# service httpd graceful
[[email protected] ~]# php -m |grep redis

Then update the php.ini as follows:

session.save_handler = redis
session.save_path = "tcp://127.0.0.1:6379?auth=your_secure_password_here"

On CentOS and Red Hat servers, depending on what version of PHP was installed and how, you may have to update another file as it will override the php.ini. Only change this if the values exist and are configured for files:

[[email protected] ~]# vim /etc/httpd/conf.d/php.conf
session.save_handler = redis
session.save_path = "tcp://127.0.0.1:6379?auth=your_secure_password_here"

Test to ensure sessions are now being stored in Redis:

[[email protected] ~]# vim /var/www/html/test-sessions.php
<?php
session_start();
?>
Created a session

Then run the following on the command line and confirm the returned numbers increment as shown below:

[[email protected] ~]# curl localhost/test-sessions.php && redis-cli -a your_secure_password_here keys '*' |grep SESSION | wc -l
10
Created a session
11

Troubleshooting

Confirm Redis is online:

[[email protected] ~]# redis-cli ping

How to connect using redis-cli when redis is running on a different server or using a different port:

[[email protected] ~]# redis-cli -h ip_of_redis_server -p port_number_here

Sometimes you may need to flush the Redis cache. Before doing this, make sure you are connecting to the right instance of Redis since there could be multiple instances running. An example is below:

[[email protected] ~]# redis-cli -h ip_of_redis_server -p port_number_here
FLUSHALL

To get some useful stats on Redis, run:

[[email protected] ~]# redis-cli
info

To get memory specific stats, run:

[[email protected] ~]# redis-cli
info memory
127.0.0.1:6379> info memory
# Memory
used_memory:488315720
used_memory_human:465.69M
used_memory_rss:499490816
used_memory_peak:505227288
used_memory_peak_human:481.82M
used_memory_lua:36864
mem_fragmentation_ratio:1.02
mem_allocator:jemalloc-3.6.0

To increase the memory limit assigned to Redis without restarting the service, the example shown below will increase the memory allocated dynamically from 1G to 2G without a restart of the Redis:

[[email protected] ~]# redis-cli
127.0.0.1:6379> config get maxmemory
1) "maxmemory"
2) "1000000000"
127.0.0.1:6379> config set maxmemory 2g
OK
127.0.0.1:6379> config get maxmemory
1) "maxmemory"
2) "2000000000"

Regarding performance issues with Redis, there are a number of factors that need to be account for, too many for this article. Redis published an excellent article that goes into various things that could cause latency with Redis at:
https://redis.io/topics/latency