How To Install and Configure Zabbix to Securely Monitor Remote Servers on CentOS 7

The author selected the Open Source Initiative to receive a donation as part of the Write for DOnations program.

Introduction #

Zabbix is open-source monitoring software for networks and applications. It offers real-time monitoring of thousands of metrics collected from servers, virtual machines, network devices, and web applications. These metrics can help you determine the current health of your IT infrastructure and detect problems with hardware or software components before customers complain. Useful information is stored in a database so you can analyze data over time and improve the quality of provided services, or plan upgrades of your equipment.
Zabbix uses several options for collecting metrics, including agentless monitoring of user services and client-server architecture. To collect server metrics, it uses a small agent on the monitored client to gather data and send it to the Zabbix server. Zabbix supports encrypted communication between the server and connected clients, so your data is protected while it travels over insecure networks.
The Zabbix server stores its data in a relational database powered by MySQL, PostgreSQL, or Oracle. You can also store historical data in nosql databases like Elasticsearch and TimescaleDB. Zabbix provides a web interface so you can view data and configure system settings.
In this tutorial, you will configure two machines. One will be configured as the server, and the other as a client that you’ll monitor. The server will use a MySQL database to record monitoring data and use Apache to serve the web interface.

Prerequisites #

To follow this tutorial, you will need:

Two CentOS 7 servers set up by following the Initial Server Setup with CentOS 7, including a non-root user with sudo privileges and a firewall. On one server, you will install Zabbix; this tutorial will refer to this as the Zabbix server. It will monitor your second server; this second server will be referred to as the second CentOS server.
The Zabbix server needs Apache, MySQL, and PHP installed. Follow How To Install Linux, Apache, MySQL, PHP (LAMP) Stack on CentOS 7 to configure these on your Zabbix server.

Note: CentOS uses MariaDB instead of MySQL, but this will not cause any issues while following this tutorial.

Additionally, because you will use the Zabbix server to access valuable information about your infrastructure that you would not want unauthorized users to access, it’s important that you keep your server secure by installing a TLS/SSL certificate. This is optional but strongly encouraged. You can follow the Let’s Encrypt on CentOS 7 guide to obtain a free TLS/SSL certificate.

Step 1 — Installing the Zabbix Server #

First, you need to install Zabbix on the server where you installed MySQL, Apache, and PHP. Log in to this machine as your non-root user:

ssh sammy@zabbix_server_ip_address

Zabbix isn’t available in the package manager by default, so install a repository configuration package using the official Zabbix repository for CentOS. This tutorial will use version 4.2 of Zabbix:

sudo rpm -Uvh https://repo.zabbix.com/zabbix/4.2/rhel/7/x86_64/zabbix-release-4.2-1.el7.noarch.rpm

You will see the following output:

Retrieving https://repo.zabbix.com/zabbix/4.2/rhel/7/x86_64/zabbix-release-4.2-1.el7.noarch.rpm
warning: /var/tmp/rpm-tmp.WXsYNB: Header V4 RSA/SHA512 Signature, key ID a14fe591: NOKEY
Preparing...                          ################################# [100%]
Updating / installing...
   1:zabbix-release-4.2-1.el7         ################################# [100%]

Clear all entries for currently enabled repositories from the cache:

sudo yum clean all

Then install the Zabbix server and web frontend with MySQL database support:

sudo yum install zabbix-server-mysql zabbix-web-mysql

During the installation process you will be asked about importing a GPG key. This key will verify the authenticity of the package you are installing. To allow the installation to finish, accept the GPG key by typing y and pressing ENTER when prompted to do so.
Also, install the Zabbix agent, which will let you collect data about the Zabbix server status itself.

sudo yum install zabbix-agent

Before you can use Zabbix, you have to set up a database to hold the data that the Zabbix server will collect from its agents. You can do this in the next step.

Step 2 — Configuring the MySQL Database for Zabbix #

You need to create a new MySQL database and populate it with some basic information in order to make it suitable for Zabbix. You’ll also create a specific user for this database so Zabbix isn’t logging in to MySQL with the root account.
Log in to MySQL as the root user using the root password that you set up during the MySQL server installation:

mysql -uroot -p

Create the Zabbix database with UTF-8 character support:

create database zabbix character set utf8 collate utf8_bin;

Then create a user that the Zabbix server will use, give it access to the new database, and set the password for the user:

grant all privileges on zabbix.* to zabbix@localhost identified by 'your_zabbix_mysql_password';

Then apply these new permissions:

flush privileges;

That takes care of the user and the database. Exit out of the database console:

quit;

Next, import the initial schema and data. The Zabbix installation provided you with a file that sets this up.
Run the following command to set up the schema and import the data into the zabbix database. Use zcat since the data in the file is compressed.

zcat /usr/share/doc/zabbix-server-mysql*/create.sql.gz | mysql -uzabbix -p zabbix

Enter the password for the zabbix MySQL user that you configured when prompted.
This command will not output any errors if it was successful. If you see the error ERROR 1045 (28000): Access denied for user zabbix@'localhost' (using password: YES) then make sure you used the password for the zabbix user and not the root user.
In order for the Zabbix server to use this database, you need to set the database password in the Zabbix server configuration file. Open the configuration file in your preferred text editor. This tutorial will use vi:

sudo vi /etc/zabbix/zabbix_server.conf

Note: To learn more about the text editor vi and its successor vim, check out our Installing and Using the Vim Text Editor on a Cloud Server tutorial.

Look for the following section of the file:
/etc/zabbix/zabbix_server.conf

...
### Option: DBPassword                           
#       Database password. Ignored for SQLite.   
#       Comment this line if no password is used.
#                                                
# Mandatory: no                                  
# Default:                                       
# DBPassword=
...

These comments in the file explain how to connect to the database. You need to set the DBPassword value in the file to the password for your database user. Enter insert mode by pressing i, uncomment DBPassword=, and add your password to configure the database:
/etc/zabbix/zabbix_server.conf

...
# Mandatory: no                                  
# Default
DBPassword=your_zabbix_mysql_password
...

When you’re finished, press ESC to leave insert mode, then :wq and ENTER to save and exit the file.
That takes care of the Zabbix server configuration. Next, you will make some modifications to your PHP setup in order for the Zabbix web interface to work properly.

Step 3 — Configuring PHP for Zabbix #

The Zabbix web interface is written in PHP and requires some special PHP server settings. The Zabbix installation process created an Apache configuration file that contains these settings. You need to make a small change to this file, so open it up with the following:

sudo vi /etc/httpd/conf.d/zabbix.conf

The file contains PHP settings that meet the necessary requirements for the Zabbix web interface. However, the timezone setting is commented out by default. To make sure that Zabbix uses the correct time, you need to set the appropriate timezone.
/etc/httpd/conf.d/zabbix.conf

...
<IfModule mod_php5.c>
    php_value max_execution_time 300
    php_value memory_limit 128M
    php_value post_max_size 16M
    php_value upload_max_filesize 2M
    php_value max_input_time 300
    php_value max_input_vars 10000
    php_value always_populate_raw_post_data -1
    # php_value date.timezone Europe/Riga
</IfModule>

Uncomment the timezone line, highlighted in the preceding code block, and change it to your timezone. You can use this list of supported time zones to find the right one for you. Then save and close the file.
Now restart Apache to apply these new settings:

sudo systemctl restart httpd

Note: If SELinux is running in enforcing mode, you need to put it into permissive mode using the sudo setenforce 0 command to allow the Zabbix agent to operate freely. You can use this tutorial to get more info about the Security Enhanced Linux control mechanism.

You can now start the Zabbix server and agent:

sudo systemctl start zabbix-server 
sudo systemctl start zabbix-agent 

Then check whether the Zabbix server is running properly:

sudo systemctl status zabbix-server

You will see the following status:

● zabbix-server.service - Zabbix Server
   Loaded: loaded (/usr/lib/systemd/system/zabbix-server.service; disabled; vendor preset: disabled)
   Active: active (running) since Fri 2019-05-03 05:57:29 UTC; 2s ago
  Process: 4461 ExecStart=/usr/sbin/zabbix_server -c $CONFFILE (code=exited, status=0/SUCCESS)
  ...

Finally, enable the server and agent to start at boot time:

sudo systemctl enable zabbix-server
sudo systemctl enable zabbix-agent

The server is set up and connected to the database. Next, set up the web frontend.

Note: As mentioned in the Prerequisites section, it is recommended that you enable SSL/TLS on your server. You can follow this tutorial now to obtain a free SSL certificate for Apache on CentOS 7. After obtaining your SSL/TLS certificates, you can come back and complete this tutorial.

Step 4 — Configuring Settings for the Zabbix Web Interface #

The web interface lets you see reports and add hosts that you want to monitor, but it needs some initial setup before you can use it. Launch your browser and go to the address http://zabbix_server_name/zabbix/. On the first screen, you will see a welcome message. Click Next step to continue.
On the next screen, you will see the table that lists all of the prerequisites to run Zabbix.

All of the values in this table must be OK, so verify that they are. Be sure to scroll down and look at all of the prerequisites. Once you’ve verified that everything is ready to go, click Next step to proceed.
The next screen asks for database connection information.

You told the Zabbix server about your database, but the Zabbix web interface also needs access to the database to manage hosts and read data. Therefore enter the MySQL credentials you configured in Step 2 and click Next step to proceed.
On the next screen, you can leave the options at their default values.

The Name is optional; it is used in the web interface to distinguish one server from another in case you have several monitoring servers. Click Next step to proceed.
The next screen will show the pre-installation summary so you can confirm everything is correct.

Click Next step to proceed to the final screen.
The web interface setup is complete. This process creates the configuration file /etc/zabbix/web/zabbix.conf.php which you could back up and use in the future. Click Finish to proceed to the login screen. The default user is Admin and the password is zabbix.
Before you log in, set up the Zabbix agent on your second CentOS server.

Step 5 — Installing and Configuring the Zabbix Agent #

Now you need to configure the agent software that will send monitoring data to the Zabbix server.
Log in to the second CentOS server:

ssh sammy@second_centos_server_ip_address

Then, just like on the Zabbix server, run the following command to install the repository configuration package:

sudo rpm -Uvh https://repo.zabbix.com/zabbix/4.2/rhel/7/x86_64/zabbix-release-4.2-1.el7.noarch.rpm

Next, clear the yum cache:

sudo yum clean all

Then install the Zabbix agent:

sudo yum install zabbix-agent

During the installation process you will be asked about importing a GPG key. Confirm it so the installation can complete.
While Zabbix supports certificate-based encryption, setting up a certificate authority is beyond the scope of this tutorial. Instead, this tutorial will use pre-shared keys (PSK) to secure the connection between the server and agent.
First, generate a PSK:

sudo sh -c "openssl rand -hex 32 > /etc/zabbix/zabbix_agentd.psk"

Show the key so you can copy it somewhere. You will need it to configure the host.

cat /etc/zabbix/zabbix_agentd.psk

The key will look something like this:

a4374c8c3b55de472225dbf96aa7cd3ce6a34abc95d0eb2a601d954ee0cd4410

Now edit the Zabbix agent settings to set up its secure connection to the Zabbix server. Open the agent configuration file in your text editor:

sudo vi /etc/zabbix/zabbix_agentd.conf

Each setting within this file is documented via informative comments throughout the file, but you only need to edit some of them.
First you have to edit the IP address of the Zabbix server. Find the following section:
/etc/zabbix/zabbix_agentd.conf

...
### Option: Server
#       List of comma delimited IP addresses (or hostnames) of Zabbix servers.
#       Incoming connections will be accepted only from the hosts listed here.
#       If IPv6 support is enabled then '127.0.0.1', '::127.0.0.1', '::ffff:127.0.0.1' are treated equally.
#
# Mandatory: no
# Default:
# Server=

Server=127.0.0.1
...

Change the default value to the IP of your Zabbix server:
/etc/zabbix/zabbix_agentd.conf

...
# Mandatory: no
# Default:
# Server=

Server=zabbix_server_ip_address
...

Next, find the section that configures the secure connection to the Zabbix server and enable pre-shared key support. Find the TLSConnect section, which looks like this:
/etc/zabbix/zabbix_agentd.conf

...
### Option: TLSConnect
#       How the agent should connect to server or proxy. Used for active checks.
#       Only one value can be specified:
#               unencrypted - connect without encryption
#               psk         - connect using TLS and a pre-shared key
#               cert        - connect using TLS and a certificate
#
# Mandatory: yes, if TLS certificate or PSK parameters are defined (even for 'unencrypted' connection)
# Default:
# TLSConnect=unencrypted
...

Then uncomment TLSConnect= and replace unencrypted with psk to configure pre-shared key support:
/etc/zabbix/zabbix_agentd.conf

...
TLSConnect=psk
...

Next, locate the TLSAccept section, which looks like this:
/etc/zabbix/zabbix_agentd.conf

...
### Option: TLSAccept
#       What incoming connections to accept.
#       Multiple values can be specified, separated by comma:
#               unencrypted - accept connections without encryption
#               psk         - accept connections secured with TLS and a pre-shared key
#               cert        - accept connections secured with TLS and a certificate
#
# Mandatory: yes, if TLS certificate or PSK parameters are defined (even for 'unencrypted' connection)
# Default:
# TLSAccept=unencrypted
...

Configure incoming connections to support pre-shared keys by uncommenting TLSAccept= and adding psk:
/etc/zabbix/zabbix_agentd.conf

...
TLSAccept=psk
...

Next, find the TLSPSKIdentity section, which looks like this:
/etc/zabbix/zabbix_agentd.conf

...
### Option: TLSPSKIdentity
#       Unique, case sensitive string used to identify the pre-shared key.
#
# Mandatory: no
# Default:
# TLSPSKIdentity=
...

Choose a unique name to identify your pre-shared key by uncommenting TLSPSKIdentity= and adding the highlighted code:
/etc/zabbix/zabbix_agentd.conf

...
TLSPSKIdentity=PSK 001
...

You’ll use this as the PSK ID when you add your host through the Zabbix web interface.
Then set the option that points to your previously created pre-shared key. Locate the TLSPSKFile option:
/etc/zabbix/zabbix_agentd.conf

...
### Option: TLSPSKFile
#       Full pathname of a file containing the pre-shared key.
#
# Mandatory: no
# Default:
# TLSPSKFile=
...

Uncomment TLSPSKFile= and add this text to point the Zabbix agent to the PSK file you created:
/etc/zabbix/zabbix_agentd.conf

...
TLSPSKFile=/etc/zabbix/zabbix_agentd.psk
...

Save and close the file. Now you can start the Zabbix agent and set it to start at boot time:

sudo systemctl start zabbix-agent
sudo systemctl enable zabbix-agent

For good measure, check that the Zabbix agent is running properly:

sudo systemctl status zabbix-agent

You will see the following status, indicating the agent is running:

● zabbix-agent.service - Zabbix Agent
   Loaded: loaded (/usr/lib/systemd/system/zabbix-agent.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2019-05-03 06:25:06 UTC; 28s ago
  ...

The agent will listen on port 10050 for connections from the server. In order to configure access coming from specific IP addresses or subnets, use the rich rule functionality of firewalld:

sudo firewall-cmd --permanent --zone=public --add-rich-rule='rule family="ipv4" source address="zabbix_server_ip_address/32" port protocol="tcp" port="10050" accept'

Rich rules allow you to create more complex and customizable firewalld rules to gain greater control over your firewall. In this command, you are adding a rule that accepts ipv4 traffic from the source, which you have set as the IP address of the Zabbix server, to port 10050 of your second CentOS server.
Next, reload firewalld to activate the new rule:

sudo firewall-cmd --reload

Your agent is now ready to accept connections and send data to the Zabbix server. But in order to use it, you have to link to it from the server’s web console. In the next step, you will complete the configuration.

Step 6 — Adding the New Host to the Zabbix Server #

Installing an agent on a server you want to monitor is only half of the process. Each host you want to monitor needs to be registered on the Zabbix server, which you can do through the web interface.
Log in to the Zabbix server web interface by navigating to the address http://zabbix_server_name/zabbix/.

When you have logged in, click on Configuration, and then Hosts in the top navigation bar. Then click the Create host button in the top right corner of the screen. This will open the host configuration page.

Adjust the Host name and IP address to reflect the host name and IP address of your second CentOS server, then add the host to a group. You can select an existing group, for example Linux servers, or create your own group. The host can be in multiple groups. To do this, enter the name of an existing or new group in the Groups field and select the desired value from the proposed list.
Once you’ve added the group, click the Templates tab.

Type Template OS Linux in the Search field and then click Add immediately under the search bar to add this template to the host.
Next, navigate to the Encryption tab. Select PSK for both Connections to host and Connections from host and uncheck No encryption for Connections from host. Then set PSK identity to PSK 001, which is the value of the TLSPSKIdentity setting of the Zabbix agent you configured previously. Then set PSK value to the key you generated for the Zabbix agent. It’s the one stored in the file /etc/zabbix/zabbix_agentd.psk on the agent machine.

Finally, click the Add button at the bottom of the form to create the host.
You will see your new host in the list. Wait for a minute and reload the page to see green labels indicating that everything is working fine and the connection is encrypted.

If you have additional servers you need to monitor, log in to each host, install the Zabbix agent, generate a PSK, configure the agent, and add the host to the web interface following the same steps you followed to add your first host.
The Zabbix server is now monitoring your second CentOS server. Now, set up email notifications to be notified about problems.

Step 7 — Configuring Email Notifications #

Zabbix automatically supports several types of notifications: email, Jabber, SMS, etc. You can also use alternative notification methods, such as Telegram or Slack. You can see the full list of integrations here.
The simplest communication method is email, and this tutorial will configure notifications for this media type.
Click on Administration, and then Media types in the top navigation bar. You will see the list of all media types. Click on Email.
Adjust the SMTP options according to the settings provided by your email service. This tutorial uses Gmail’s SMTP capabilities to set up email notifications; if you would like more information about setting this up, see How To Use Google’s SMTP Server.

Note: If you use 2-Step Verification with Gmail, you need to generate an App Password for Zabbix. You don’t need to remember it, you’ll only have to enter an App password once during setup. You will find instructions on how to generate this password in the Google Help Center.

You can also choose the message format—html or plain text. Finally, click the Update button at the bottom of the form to update the email parameters.

Now, create a new user. Click on Administration, and then Users in the top navigation bar. You will see the list of users. Then click the Create user button in the top right corner of the screen. This will open the user configuration page.

Enter the new username in the Alias field and set up a new password. Next, add the user to the administrator’s group. Type Zabbix administrators in the Groups field and select it from the proposed list.
Once you’ve added the group, click the Media tab and click on the Add underlined link. You will see a pop-up window.

Enter your email address in the Send to field. You can leave the rest of the options at the default values. Click the Add button at the bottom to submit.
Now navigate to the Permissions tab. Select Zabbix Super Admin from the User type drop-down menu.
Finally, click the Add button at the bottom of the form to create the user.
Now you need to enable notifications. Click on the Configuration tab, and then Actions in the top navigation bar. You will see a pre-configured action, which is responsible for sending notifications to all Zabbix administrators. You can review and change the settings by clicking on its name. For the purposes of this tutorial, use the default parameters. To enable the action, click on the red Disabled link in the Status column.
Now you are ready to receive alerts. In the next step, you will generate one to test your notification setup.

Step 8 — Generating a Test Alert #

In this step, you will generate a test alert to ensure everything is connected. By default, Zabbix keeps track of the amount of free disk space on your server. It automatically detects all disk mounts and adds the corresponding checks. This discovery is executed every hour, so you need to wait a while for the notification to be triggered.
Create a temporary file that’s large enough to trigger Zabbix’s file system usage alert. To do this, log in to your second CentOS server if you’re not already connected.

ssh sammy@second_centos_server_ip_address

Next, determine how much free space you have on the server. You can use the df command to find out:

df -h

The command df will report the disk space usage of your file system, and the -h will make the output human-readable. You’ll see output like the following:

Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        25G  958M   25G   4% /

In this case, the free space is 25GB. Your free space may differ.
Use the fallocate command, which allows you to pre-allocate or de-allocate space to a file, to create a file that takes up more than 80% of the available disk space. This will be enough to trigger the alert:

fallocate -l 20G /tmp/temp.img

After around an hour, Zabbix will trigger an alert about the amount of free disk space and will run the action you configured, sending the notification message. You can check your inbox for the message from the Zabbix server. You will see a message like:

Problem started at 10:49:25 on 2019.05.03
Problem name: Free disk space is less than 20% on volume /
Host: Second Centos Server
Severity: Warning

Original problem ID: 34

You can also navigate to the Monitoring tab, and then Dashboard to see the notification and its details.

Now that you know the alerts are working, delete the temporary file you created so you can reclaim your disk space:

rm -f /tmp/temp.img

After a minute Zabbix will send the recovery message and the alert will disappear from the main dashboard.

Conclusion #

In this tutorial, you set up a simple and secure monitoring solution that will help you monitor the state of your servers. It can now warn you of problems, and you have the opportunity to analyze the processes occurring in your IT infrastructure.
To learn more about setting up monitoring infrastructure, check out How To Install Elasticsearch, Logstash, and Kibana (Elastic Stack) on CentOS 7 and How To Gather Infrastructure Metrics with Metricbeat on CentOS 7.