Laravel gives 502 error upon validation failure form submit - php

Question

I have an update form, which updates my database with the given inputs. I use the Laravel validation to make an update validator to check if the given e-mail is unique or not (if it's not it should throw me the validation error and reload the update page).
This is my validator:
public function rules()
{
$contact_guid = $this->route('contact_guid');
return [
'contact_email' => [
Rule::unique('contact')->ignore($contact_guid, 'contact_guid'),
],
];
}
public function messages()
{
return [
'contact_email.required' => 'E-mail is required.',
'contact_email.unique' => 'This e-mail is already in use.',
];
}
The problem appears to be that some contacts give the 502 error with certain unique emails and other contacts get the 502 error on different unique emails. I've noticed that once I remove 'contact_email.unique' => 'This e-mail is already in use.', that my application works fine and it doesn't give me the 502 error.
Edit:
I found that how longer the message is at 'contact_email.unique' => 'This e-mail is already in use.',, it gives me the 502 bad gateway more often.

Answer 1

In my case it happened due to nginx not being configured to deal with big headers, I saw this in the logs:
upstream sent too big header while reading response header from upstream
The solution was to add these lines to the nginx configuration:
fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;

Answer 2

A HTTP 502: Bad Gateway response is not one that would by default be output by Laravel, but would be output by your server:
The HyperText Transfer Protocol (HTTP) 502 Bad Gateway server error response code indicates that the server, while acting as a gateway or proxy, received an invalid response from the upstream server.
It is entirely possible that the invalid response however is stemming from your application, and so would make sense to make an attempt at debugging it.
There are potentially a wider number of causes for such a problem, here is a brief overview of them and potential fixes:
Ensure you have debug enabled in your Laravel .env file and have cleared the cache.
File Permissions are incorrectly set. Should be (depending on server but general rule of thumb) 644 for files and 755 for folders/directories.
An error in one of the PHP Files - Try enabling the display_errors option in your PHP configuration.
PHP Memory & Process limitations - Try increasing your memory_limit in your PHP configuration.
Other PHP Process Limitations - Check with server admin/hosting provider
Corrupt PHP Modules, Extensions, Builds - Check with server admin/hosting provider
The obscure - If points 1-6 don't produce a fix typically the best course of action is to check the Apache Error Logs.
TL;DR: You need to have your Network/System Administrator identify the cause of the HTTP 502. Apache Error Logs will likely give you a very good indication.

Answer 3

I had the same issue. Increasing the buffer size fixed it. Moreover, I was using cookies as the session driver in my app, I guess the ~1kb session cookie was taking up all the buffer?
Changed session driver to file/database fixed the issue as well