On an all default Ubuntu 16.04 Nginx environment hosted on a 20$ DigitalOcean droplet I have only one WordPress site with a small amount of data: About 10 webpages, 10 images (around 100kb each), and 6 common plugins (all in default configuration).
I experience a bit of a slow general loading time (TTFB), in this site.
WordPress caching (AutoPtimize):
Since I uploaded the site, about a month and half ago, I keep getting the following error, in each Google PageSpeed Insights test (GPI):
Reduce server response time
In our test, your server responded in 0.95 seconds. There are many factors that can slow down your server response time. Please read our recommendations to learn how you can monitor and measure where your server is spending the most time.
It's always 0.93 to 1.20 although I feel, intuitively, that it should have been much lower than that, per the data I've given.
Why WordPress isn't the problem
The site's theme is Astra, without a subtheme. The same problem happened with other themes as well.
I have enabled CSS-JS minification, resource compression and WordPress caching with the plugin AutoPtimize as well as Nginx caching (see below).
I tried to turn off all plugins, yet no serious change was seen; I went down from 900ms to around 450ms while still having the error.
Given that all my tests indicate that this is an Nginx/PHP problem, what do I lack in my Nginx/PHP configuration to have a much lower loading time (say up to 0.10)? Everything is default for both, so I can't say what will be bad in that.
Activating the free plan of Cloudflare with full (strict) SSL processing, didn't bring any TTFB significant change.