Blitz caches HTML with urls to "generate-transform actions"

[ostark]

Hi Ben

One of our (fortrabbit) clients reported traffic spikes (10K instead of 100K requests per hour) recently. We noticed massive requests to urls like /index.php?p=actions/assets/generate-transform&transformId={transformId}.

When having a look at the html responses, we noticed that Blitz was the reason, since the URLs were cached.

The Craft {% cache %} prevents it actively
https://github.com/craftcms/cms/blob/3.1/src/services/TemplateCaches.php#L272

Is this implemented in Blitz as well? Is there a setting?
Or should the "template developer" take care of it?

Cheers,
Oli

Hi Oliver, as you correctly noticed, Blitz caches pages even if they contain URLs with the assets/generate-transform action. One workaround could be to enable the generateTransformsBeforePageLoad config setting, but it would probably make sense to prevent Blitz from caching such pages by default. Do you see any possible downsides to this?

[ostark]

I'm not a fan of generateTransformsBeforePageLoad. Async calls make much more sense.
I'd suggest preventing caching if assets/generate-transform is in the response body, like Craft does.

Agreed, will look into adding this in the next release. Thanks for reporting it!

One issue I can see is that warming the cache will not be as predictable, as Blitz currently uses Guzzle to make calls to the pages that need warming, so no AJAX requests. I'll need to consider either a workaround or maybe make this an opt-in config setting.

Changed the behaviour in version 2.2.0
https://github.com/putyourlightson/craft-blitz/blob/v2/CHANGELOG.md#220---2019-09-14