Adds thumbnails-permanent for specific host

[enejb]

I am not sure if this is the right approach here.

The problem that I am trying to solve it make sure that under some domains (that we control such as public-api.wordpress.com) we don't clear the cache and are always able to serve an image.

[lsl]

I don't know enough about the way this storage / caching works to confidently comment here but I'll do my best to make some educated guesses.

My concern with this particular approach would be that if we ever generate mshots for something on public-api that is dynamic it will never, ever, clear.

For example, this would create problems for something like the design previews if we started adding customers site names to the screenshots.

There is a proposal floating around for re-working mshots to have an option to return the image in realtime - that is don't redirect, make the connection wait for the screenshot to be taken. This would help us avoid needing to poll for images like we do in calypso's MShotsImage component.

Another option would be to implement this to work with a given option only (?permanent=true or ?ttl=86400) But these likely still run into the situation where a server might clear, a new server might be spun up or you simply hit a new server without the image. (mshots is loadbalanced across a few servers iirc)

[bazza]

All local storage is ephemeral, so if you want permanent storage you will need to utilize object storage.