What are the tools for monitoring the status of sites using a VPS server?

Question

Monitoring

Hello.
Suppose I have 10 sites on one VPS server. One of them "fell" and began to issue a 404 error (or another) to all visitors. Until I go to the site or look at the logs - I will not know anything about the problem.
How can I get information about this problem using the server ? By Email, phone, on the server command line or something else. Please tell me the tools for this.
ubuntu server 16.04.

Answer 1

for this, there are a lot of third-party services that periodically poll the specified sites and if something goes wrong, they send notifications.
Of course, you can deploy and configure the monitoring system yourself (nagios / zabix / etc), but IMHO in this case this is superfluous.

Answer 2

Plus a comment from above, if you need it on your knee - make a task in the crown for "once a minute", where there will be a script that checks
response=$(curl --write-out %{http_code} --silent --output /dev/null servername)
where servername = name of the site we are checking

Answer 3

Take someone who created 10 sites and give him the task of writing such a tool.