Why is the load average going up?

Question

linux

On the server, at times of peak load, the load average sometimes increases for short periods of time.
But I can't understand why.
Ran atop to record readings.
At the moment LA > 15
i.imgur.com/HGpx8PN.png You
can see that the CPU, disk and memory are in the same state when LA was ~= 4, about 10 minutes ago
i.imgur.com/xMEQYpP.png
As far as I understand LA ( load average) - this is roughly speaking a certain average number of processes that are in a state of waiting for resources over the last minute / 5 minutes / 15 minutes.
Based on this, I conclude that the problem is not in the Processor / Disks / Memory, but in the network.
Am I right in thinking that in the future, with an increase in the number of requests to the server, it will be the network that will be the bottleneck? How can this problem be diagnosed not by elimination, but by analysis?
Could someone please explain LA's dependency on the network. My specific example:
nginx + apache work on this server, nginx gives statics, php is proxied to apache, the database is on another server, that is, php makes a connect to another server.
In what cases can LA rise ?

Answer 1

Here is some theory:
https://habrahabr.ru/post/216827/
https://habrahabr.ru/post/260335/