ref
https://linear.app/tryghost/issue/KTLO-45/deploy-members-caching-solution-to-a-single-site-to-validate-and-test
Currently we only cache publicly available content. Any content that is
accessed by a logged in member is only cached for that specific member
based on their cookie. As a result, almost all requests from logged in
members bypass our caching layer and reach Ghost, which adds unnecessary
load to Ghost and its database.
This change adds experimental headers that allow our CDN to understand
which tier to cache the content against, and securely tell the CDN which
tier a logged in member has access to. With these changes, we can cache
the member content against the tier, rather than the individual member,
which should result in a higher cache HIT ratio and reduce the load on
Ghost.
For requests to the frontend of the site, Ghost will set a custom
`X-Member-Cache-Tier` header to the ID of the tier of the member who is
accessing the content. This tells the CDN which tier to cache the
content against.
For requests to either `/members/?token=...` endpoint (the magic link
endpoint) or `/members/api/member`, Ghost will set a `ghost-access` and
`ghost-access-hmac` cookie with the ID of the tier of the logged in
member. With these two pieces of information, our CDN can serve cached
content to logged in members.
These headers are experimental, and can only be enabled via Ghost's
config. To enable these headers, set `cacheMembersContent:enabled` to
`true` and provide an HMAC key in `cacheMembersContent:hmacSecret`.
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