I have just setup a VPS at scaleway. Running CWP.
I have install Varnish:80, NGINX:82 &:443, Apache :8181.
I setup a test WP site. Setup with Letsencrpyt certs. Setup Nginx with Http2. Using PHP7.
I test my site and it hits the varnish cache.
On pingdom I get faster than 92% of tested websites. (No caching plugins yet)
http://tools.pingdom.com/fpt/ch6gYR/https://test.mariselaveludo.com I loaded up 100 VU's from loadimpact over 3 different locations over a 5min period, results:
Page 1 Aggregated (World) Auto generated from test.mariselaveludo.com 549 238.9ms 2.66s 3.74s Add graph
Page 1 Ashburn, US (Amazon) Auto generated from test.mariselaveludo.com 192 825.47ms 952.58ms 1.97s Add graph
Page 1 Dublin, IE (Amazon) Auto generated from test.mariselaveludo.com 190 238.9ms 283.49ms 466.53ms Add graph
Page 1 Sydney, AU (Amazon) Auto generated from test.mariselaveludo.com 167 3.28s 3.4s 3.74s Add graph
Here is my varnishstat from that period:
Uptime mgt: 0+01:55:02 Hitrate n: 10 100 1000
Uptime child: 0+01:55:02 avg(n): 0.0000 0.2450 0.2331
NAME CURRENT CHANGE AVERAGE AVG_10 AVG_100 AVG_1000
MAIN.uptime 0+01:55:02
MAIN.sess_conn 4889 0.00 . 0.00 5.03 3.56
MAIN.client_req 4908 0.00 . 0.00 5.03 3.57
MAIN.cache_hit 4665 0.00 . 0.00 5.03 3.56
MAIN.cache_miss 46 0.00 . 0.00 0.00 0.00
MAIN.backend_reuse 49 0.00 . 0.00 0.00 0.00
MAIN.backend_recycle 63 0.00 . 0.00 0.00 0.00
You can see that it hits Varnish cache. So I dont see a problem enabling https site wide.