Merged CSS/JS files require pub/static/_cache writeable, contrary to documentation

[scottsb]

Preconditions

1. Have Magento installed with two filesystem owners as documented, with all code files (source and CLI-generated) read-only for web server user. This includes the full pub/static directory.
2. Turn on the merging of CSS or JS files.

Steps to reproduce

Clear static file cache and load home page.

Expected result

No exception should be generated.

Actual result

Exception is logged:

[2018-01-16 16:18:56] main.CRITICAL: Directory "/var/www/html/___/pub/static/_cache/merged" cannot be created Warning!mkdir(): Permission denied {"exception":"[object] (Magento\\Framework\\Exception\\FileSystemException(code: 0): Directory \"/var/www/html/___/pub/static/_cache/merged\" cannot be created Warning!mkdir(): Permission denied at /var/www/html/___/vendor/magento/framework/Filesystem/Driver/File.php:225)"} []

Commentary

This could arguably be seen as a documentation issue in which case I can report it in the devdocs repo. However, as I understand it, it seems that the documentation does describe the intended state, meaning the code should be changed instead. I'm not sure if it's possible, but if it were, ideally the merged files would be generated by static-content:deploy as alluded to in #9542. This would allow multiple servers in a cluster to be certain to have the merged files present in response to requests without the directory being shared among the nodes.

[davidalger]

+1 here guys! Nothing should be written to pub/static when in production mode, and a setup:static-content:deploy should write out merged files to static/_cache. This causes problems in load-balanced environments where a snapshot of a pre-compiled build is deployed.

[dan-ding]

bump
sort of related: #9542

Hi @scottsb i cannot reproduce you scenario, which version of magento you've tested ?

[graemel]

I see this behaviour in 2.1.

[davidalger]

This is a problem with 2.2.x as well. It starts with the files in static/_cache/merged not being written during static content deploy, and then the issue is compounded (on either a read-only file system or ) when Magento attempts to write merged JS / CSS files to disk during a web request.

@scottsb , we are closing this issue due to inactivity. If you'd like to update it, please reopen the issue.

[ishakhsuvarov]

@davidalger @scottsb Sorry for the confusion. This ticket was closed mistakenly. We will take a look at it again and let you know.