Knowledgebase

Introduction

Memcached is an open-source, distributed, in-memory object caching system. It is mainly used for speeding up dynamic web applications by storing chunks of data from the results of database calls and page rendering.

In this guide, we will install and secure Memcached on CentOS 7.

##Installing Memcached

First, update the system:

yum update -y

Next, install the official Memcached package memcached; as well as libmemcached, which provides several utilities to work with Memcached:

yum install -y memcached libmemcached

Memcached will now be installed as a service.

To start Memcached at boot, use the systemctl command:

systemctl enable memcached

##Configuring Memcached

Let's bind Memcached to the local interface and disable the UDP port to avoid potential DDOS attacks. Open the /etc/sysconfig/memcached file in your favorite editor:

nano /etc/sysconfig/memcached

Find this line in the file:

OPTIONS=""

Change it to the following:

OPTIONS="-l 127.0.0.1 -U 0"

Save the file and exit the editor.

Restart Memcached to apply your changes:

systemctl restart memcached

You can ensure that it is running by using systemctl:

systemctl status memcached

The output will resemble the following:

● memcached.service - Memcached
Loaded: loaded (/usr/lib/systemd/system/memcached.service; enabled; vendor preset: disabled)
Active: active (running) since Thu 2019-04-04 17:01:41 UTC; 8s ago
Main PID: 31312 (memcached)
CGroup: /system.slice/memcached.service
        └─31312 /usr/bin/memcached -u memcached -p 11211 -m 64 -c 1024 -l 127.0.0.1 -U 0

Apr 04 17:01:41 docs systemd[1]: Started Memcached.

You can verify Memcached is bound only to the local interface and listening only to TCP connections with the ss command:

ss -plunt | grep memcached

tcp    LISTEN     0      128    127.0.0.1:11211                 *:*                   users:(("memcached",pid=31312,fd=26))

There are also a few other options that can be modified in the /etc/sysconfig/memcached configuration file:

• CACHESIZE: Caps the amount of memory available to Memcached. The default is 64 MB.
• PORT: Specifies on which port Memcached should listen. The default port is 11211.
• USER: Specifies which user the service will use to run. By default, the service will run as memcached.
• MAXCONN: Caps the number of concurrent connections. The default is 1024.

##Verifying Memcached Setup

Now, you can verify the set up using the memstat command from the libmemcached package:

memstat --servers="localhost"

The output will resemble the following:

Server: localhost (11211)
    pid: 31312
    uptime: 385
    time: 1554397684
    version: 1.4.15
    libevent: 2.0.21-stable
    pointer_size: 64
    rusage_user: 0.006269
    rusage_system: 0.014105
    curr_connections: 1

...

##Conclusion

In this guide, we covered how to install and configure Memcached and used memstat to fetch stats. The libmemcached package also comes with a few other utilities that can aid in interacting with Memcached.