Unable to Add Products Manually in Configurable Product

[apiuser]

Feature request from rkhoury82, posted on GitHub Mar 31, 2016

Steps to reproduce

1. Install Magento 2.0.3
2. Migrate or create a Configurable Product with 300 variations, save.
3. Go back into that product, press the "add products manually"

Expected result

1. With products with smaller variation sets the functionality works
2. I have increased the LimitRequestLine to work around 414 (Request-URI Too Large) error (per issue #3495)
3. I have not been able determine the size limit yet.

Actual result

1. Error Message Pops: Attention Something went wrong.
2. No browser messages in console.
3. Error in Apache Logs:

[Thu Mar 31 18:34:14.139835 2016] [proxy_fcgi:warn] [pid 4968] [client 60.225.85.XXX:37893] AH02536: couldn't encode envvar 'QUERY_STRING' in 16384 bytes, referer: http://EXAMPLE/admin/catalog/product/edit/id/3/key/81f78988e9908f8d89115a62f01eacdd8611886ce257a56bd...

[Thu Mar 31 18:34:14.139840 2016] [proxy_fcgi:warn] [pid 4968] [client 60.225.85.XXX:37893] AH02536: couldn't encode envvar 'REQUEST_URI' in 16384 bytes, referer: http://EXAMPLE/admin/catalog/product/edit/id/3/key/81f78988e9908f8d89115a62f01eacdd8611886ce257a56bd...

Environment

1. PHP 7.0.4 run as FPM not MOD_PHP (unable to test with 7.0.2 or 7.0.3 to see if it is a PHP error)
2. Apache 2.4.18
3. MYSQL 5.6

[apiuser]

Comment from PieterCappelle, posted on GitHub Aug 23, 2016

Same problem still exists in 2.1. In my case problem was fixed updating max_input_vars to 5000 in PHP7.