Magento 2 : Error 503 first byte timeout

Question

Getting this error when i'm update product from product grid using update attributes.

Error Page:

Answer 1

It's caused by Varnish limits. Try to increase your memory_limit and max_execution_time in your php.ini and pub/.user.ini files.

If you use Fastly, navigate to admin -> stores -> configuration -> Advance -> System -> Full Page Cache, set Admin path timeout to 600, and click on "Upload VCL to Fastly", this will increase the first-byte timeout in Fastly (600 is the max).

Answer 2

Same error had happened to me , it is happening because of execution time out , you can increase it for magento by using ini_set() in app/bootstrap.php.

Update attributes also consumes a lot of memory depending on the number of products selected so you may also want to increase memory limit.

So, finally paste following code at the top of app/bootstrap.php

ini_set('memory_limit' , -1);
ini_set ( 'max_execution_time', 18000);