Best way to assess site resource needs?

[Clover13]

I'm not a server/hardware guy, so learning as I go.  I've been with two different hosts, and as my site has grown have had to upgrade plans.  What is the best way to determine your site's actual needs and to ensure you are in the "right" plan that effectively supports your sites needs now and in the near future (can't be indefinite as hopefully your site grows and you'll need to re-assess and likely upgrade to support it).

This is a balance between budgeting for a reasonable server spec versus throwing away money with some kind of overkill server spec versus being totally underpowered and the site performance sucking (or being temporarily good, but outgrowing your plan quickly).

What are the metrics to review in order to determine a plan to match/meet it?  I know they say CPU, Memory, hard disk space, etc requirements...but what can I look at either diag/metric log wise, analytics wise, etc to determine how to spec this properly and make sure a given host isn't pushing for a larger than needed plan to help their own business?

[AlexJ]

Speaking based on my limited experience - I will monitor my peak usage and then I will add 20-30% extra resources to it for the spikes which can happen randomly. If I am reaching my peak hardware usage once a day daily, I would upgrade the hardware itself because peak usage = slow down when swap is getting used hard on regular basis or CPU is going to 100% time for pro-long time. 

I don't think their would be any solid formula. Just monitor your usage and based on that make a call keeping your past usage in mind. 

[Clover13]

Thanks @AlexJ!  What do you use or review to monitor it?  I've been on Shared and Managed VPS, so what I have access to varies.  I could just ask the host and hope they are honest about it or can provide the logs.  Right now, I see in my cPanel what my current usage is and in my diag logs, but my host is saying is that "CloudLinux limits set high it (cPanel?) isn't detecting the correct usage properly."

That's what provoked this topic here, as I'm not seeing the same thing my host is reporting and don't know how I can assess it better myself.

[Morgin]

Depends what you are using, but typically  apache2buddy https://www.google.ca/amp/s/www.techrepublic.com/google-amp/article/how-to-tune-apache-in-seconds-with-apache2buddy-pl/ and mysqltuner https://www.linode.com/docs/databases/mysql/how-to-optimize-mysql-performance-using-mysqltuner/ are good tools to start with.