Installing and configuring Memcached on CentOS

Memcached is an in-memory caching service based on a hash table. It's used to cache web page output, database query results, and other data with a defined expiry time. Data is accessed by key.

Memcached can also be installed in one click when placing an order — see One-Click-Apps for details.

Installation

Update the system:

yum update

Install Memcached:

yum install memcached

Configuration

Open the configuration file:

vim /etc/sysconfig/memcached

Make sure the following parameters are present:

PORT="11211"
USER="memcached"
MAXCONN="256"
CACHESIZE="64"
OPTIONS="-l 127.0.0.1"

Parameter descriptions:

• PORT — the port Memcached listens on. Default is 11211.
• USER — the user account the daemon runs under.
• MAXCONN — the maximum number of simultaneous connections.
• CACHESIZE — memory allocated for the cache in MB. 64 MB works well for most small and medium sites. For high-traffic servers, consider increasing this to 512 or 1024.
• OPTIONS="-l 127.0.0.1" — restricts Memcached to localhost only, blocking external connections. The default value is INADDR_ANY (all interfaces).

Enable Memcached at startup and start the service:

systemctl enable memcached
systemctl start memcached

Installing the PHP extension

Install the required dependencies:

yum install php-pear pecl_http php-devel

Install the extension via PECL:

pecl install memcache

If PECL asks about session handler support, press Enter to accept the default:

Enable memcache session handler support? [yes]

Restart your web server. For php-fpm:

service php-fpm reload

For Apache:

systemctl restart httpd

Verifying the setup

Check that the Memcached daemon is running:

ps -aux | grep memcached

Verify the service settings:

echo "stats settings" | nc localhost 11211

To confirm the PHP extension is active, create a phpinfo file:

echo "<?php phpinfo(); ?>" > /var/www/html/php_info.php

Open it in a browser and check that the memcache section appears in the output.

Firewall configuration

To allow connections to Memcached from a trusted IP range, add the following iptables rules:

iptables -A INPUT -p tcp --destination-port 11211 -m state --state NEW -m iprange --src-range 192.168.1.10-192.168.1.15 -j ACCEPT
iptables -A INPUT -p udp --destination-port 11211 -m state --state NEW -m iprange --src-range 192.168.1.10-192.168.1.15 -j ACCEPT