When switching 502 Error

* Can you take a look in your server logs for the actual error message?
* Does it happen every single time you try to switch or only sometimes?
* Can you restart Nginx/Apache and PHP and see if the problem persists?

This is almost certainly not a problem with User Switching, just that a problem or misconfiguration on your server is manifesting itself when switching users.

I am getting the same problem. It is down to the try_files rule but I don’t know how to fix it.

This is my try_files

location / {
    try_files $cachefile $uri $uri/ /index.php$is_args$args;
}

This is the common setup used. I think problem is that it only routes GET parameters to index.php.

It needs to be modified to allow for other pages also, I am not an nginx expert though so hopefully someone can lend a hand here.

Actually I just noticed several other plugins have URLS with query parameter that don’t involve index.php and they work fine.

Also this works fine:

https://example.com/wp-login.php?action=switch_to_user&user_id=16&_wpnonce=123

However, this gives 502:

https://subdomain.example.com/wp-login.php?action=switch_to_user&user_id=16&_wpnonce=123

I think there must be something more to why this isn’t working.

I looked in nginx log and saw there was an error:

*1 upstream sent too big header while reading response header from upstream

Seems the header is larger than nginx default buffer size.

Setting this will fix it:

fastcgi_buffer_size 32k;

@codemonkeybanana Thanks so much for the follow-up!

Can you check your cookies (in your browser console) for the domain in question please?

I suspect there will be a whole bunch of cookies in there (maybe old WordPress ones), and switching user just happens to push this over the default buffer size in nginx (switching user sets two extra cookies on top of WordPress’ own cookies).

document.cookie.length == 185

Not sure if that’s what you mean?

Well that’s nothing out of the ordinary, so I’m not sure of the actual problem. Maybe your site sends a bunch of headers.

I think the default buffer size in Nginx is 8k so that’s not that hard to fill up.

Yeah, I have a debug header in there that outputs a few env vars. That might have tipped it over the edge.