Magento 2 Full Page Cache

Which attribute header of an http response represent the page was cached?

• x-magento-cache-debug=true

• x-magento-cache-debug=HIT

• x-magento-cache-debug=MISS

• x-cache-debug=HIT

• x-cache-commerce-debug=HIT

How can you purge varnish cache for a magento 2 site?

• I will flush the magento cache with non or unconfigured bin/magento setup:config:set --http-cache-hosts=

• I will flush the magento cache with ensured configured bin/magento setup:config:set --http-cache-hosts=

• Varnish command `varnishadm "ban req.url ~ ."`

• Varnish command `varnish flush all`

• Varnish command `varnishadm flush cache`

Which HTTP methods we are able to cache?

• HEAD

• PUT

• DELETE

• GET

• PATCH

While you recognized a public content page lost cache, how is your 1st sign to detect the problem?

• Maybe server error, I'm gonna check the varnish service

• Well, code problem. I will detect, search for cacheable="false" from xml

• I go for a quick check:
  php bin/magento cache:status

• I look for a research on the Internet

I set my custom data to customer session, it works on my local but I don't know why it doesn't work on staging, or production.

How can I investigate?

• I think this is a cache problem

• Depersonalize Session​, this was cleared due full page cache.

• I think this is server problem with customer session.

• I configure and extend the current customer session life time from admin.