A sudden failure of the server, depending on its purpose, can lead to the inaccessibility of one or several sites, network printers, FTP directories, etc. Server reliability depends on both the quality of the components and compliance with the operating rules.
Choose the right processing power of the server depending on the load on it. If it hosts sites, keep in mind that the more popular they are, the more often they are accessed. Install software to protect against DoS attacks (from the English denial pf service). Note that they will not help in the event of a distributed denial of service (DDoS) attack, which is carried out simultaneously from many machines infected with malware. But not all such cases are to blame for viruses. Sometimes a similar effect occurs if a link to an unpopular site is placed on another, popular one. This unintended semblance of a DDoS attack is called the Slashdot effect, after the Slashdot site, which links often lead to similar situations.
Illiterately configured server software can crash when prompted with an error. If there is a question mark in the URL after the name of the script, followed by the parameters passed to the script, the script may crash when one of these parameters is, for example, too large a number. When writing a script, it is necessary to provide protection against the transfer of unintended parameters to it, as well as saving the IP addresses of all authors of such requests in the logs.
There are frequent cases of failures in the work of servers due to an overflow of the hard disk, so you need to choose the volume of the latter with a margin. If it suddenly fails, there will be not only a failure, but also data loss - complete or partial. To avoid this, make backups periodically.
Server freeze can happen not only due to a hacker attack or software failure. This can also happen due to the poor quality of the mains voltage. Therefore, you should not neglect the use of devices such as filters and uninterruptible power supplies. The server can also freeze due to dust in its case, especially under the motherboard, as well as from swollen capacitors, which at the same time lose capacity and begin to pass high-frequency pulsations to the processor and other nodes. Also, you should not neglect the grounding of the case, because not only the electrical safety of the machine depends on this, but also the stability of its operation. A hardware watchdog timer to automatically restart when it hangs is also helpful.
Even a fully functional and functional server may become unavailable due to a malfunction of the devices located between it and the user's computer. Therefore, before looking for a malfunction in the server, be sure to make sure that the cause is not in intermediate switches and routers.
