First we will talk about some guidelines to follow when you want to upgrade your Zabbix installation.

Zabbix works with a <major>.<minor>.<patch version> numbering. What does this mean? For example, in Zabbix 2.4.1, we have three numbers—the first number is the major version number. So when Zabbix moved from 1.8 to 2.0, we had a major upgrade. The next number is our minor number. The third number is the patch version. Now when we upgrade Zabbix, it is important to know that when the patch version changes, it means that small fixes or small new features are added to Zabbix. Those features never have impact on the database, so updating binaries from your frontend and server alone should be enough.

However, when Zabbix changes the major or the minor number, new features are introduced that have probably made some changes to the database. In this case, it is important to do a database upgrade first.

Also when you download Zabbix you will sometimes see versions that are even and odd. For example, 2.4 and 2.3 releases. The odd releases in Zabbix are the test releases and you should stay away from them in production. The even release is what will be the next release in the future after testing and debugging.

Another important thing to remember is that proxies are like small Zabbix servers. It is important to update your proxies to the same version as your Zabbix server. These components must be upgraded. If you update proxies at later stages, there are chances that you might miss some data which are collecting through the old Zabbix proxy server together.

Agents on the other hand can still work even if they run the most basic version of Zabbix. But don't forget that new versions bring new features, so you probably miss some features and some improvements on stability, memory usage, and so on.