Caching server possible issue?

[Idealproductsales]

For the last 2 days I have been consistently getting random 502 Bad gateway errors on forum posts ..

Screen shot attached.

Ive noticed that it MOST OFTEN happens when I try to go to the last page of a thread, or read a new thread.. it appears as if there is some random issue with nginx server...

Screen shot attached - shows all the 502's (each is a different thread I attempted to access)

Usually when I am browsing forums , I'll right click and open thread in new tab so I don't "lose my place" in the threads listing view..

The following all give me a 502 Bad Gateway error (even on refresh or reload or copy/paste)

http://meetup.ebid.net/showthread.php?t=134656
http://meetup.ebid.net/showthread.php?t=132372&page=2
http://meetup.ebid.net/showthread.php?t=134778
http://meetup.ebid.net/showthread.php?t=134778
http://meetup.ebid.net/showthread.php?t=134765&page=2
http://meetup.ebid.net/showthread.php?t=134792
http://meetup.ebid.net/showthread.php?t=134797
http://meetup.ebid.net/showthread.php?t=134798
http://meetup.ebid.net/showthread.php?t=134799

And, just to test, I went back to the thread listing page I was clicking from (my "master list" so to speak) and tried clicking through directly to view a thread... http://meetup.ebid.net/showthread.php?t=134728&page=2 - same result : 502 Bad gateway nginx/0.7.62

Seems like there may be some issue with the cache (frontend) communicating with the backend servers (if that's how nginx is set up, that is)

In any case, Ive been finding the forums troublesome to read the last couple of days..

Strange that we havent been having others complain.. LOL maybe it's just that I'm unlucky and just happen to be trying to read forums when the problem is happening

[CarnoustieCats]

... I was getting Bad Gateway (only on new posts) this afternoon think it was 504 tho'. I signed out of the Forums and signed in again and it seemed to cure it.

If that doesn't work I restart computer and that cures it for sure. Haven't a clue what I am doing but it works

[Idealproductsales]

yeah only way I could even get here to read your reply to begin with is to hit the "reply" link from user CP subscribed threads - couldnt get to it any other way..

I doubt that computer reboot solved the problem, since it seems to be entirely a toss-up whether the page will load for me or not - it's random- sometimes they will load, sometimes not - I doubt it has anything to do with client side...

However- it *is* possible, I think , if for some reason nginx needs information from browser (session cookie perhaps) that is getting corrupted somewhere (but then.. if that is the case, why do other threads load just fine?)

Since I didnt set up and configure Nginx, it's difficult to tell for sure just where the problem might be.. a lot depends on how it was set up.. (Pages seem to serve fine when nginx passes off the request to the apache server (if it is indeed apache on the backend) - but get screwed up when trying to serve from cache.. )

Even when posting the OP , I got a 502 right after I posted , and it re-directed (or tried to) to the freshly done thread.

only way I even knew it had gotten posted and replied to, was via the User CP subscribed threads listing

[CarnoustieCats]

...User CP subscribed threads? - forgot all about that - thanks, will try that next time

[Idealproductsales]

I'm betting it has to do with cookies or session data ... expired cookie cache or something..

I finished up the remaining items on my to-do that I had left browser open for.. tested viewing listings in I.E. and they worked fine.. tested again in FF, and still got 502's (on the same pages that IE had no trouble loading)

So.. Closed out Firefox completely, and then re-opened again so as to get new cache in place.. and now everything's working again...

So, I'm guessing nginx was looking at the tokens my browser was sending and couldnt fetch a match from apache, which caused the communication breakdown (You'd think nginx could deliver something than plain white "502 error" page .. at least put up an ErrorDocument 502 and hand off a page with a few suggestions on how to resolve before reporting it as a bug.. hehe

Doing a little research on the subject it does seem that this issue is not all that uncommon with caching servers (and now I remember *YEARS* ago we had the same exact issue with a couple of clients that we were running Tux - (another caching server) in front of apache, and got nearly the same issues, if I recall.. but their issue was they had too-strict security settings on I.E. , or some such.. memory's hazy on the details.. )

In any case, while it may be a "bug" of extremely minor proportions and only occurs for a small selection of "power users" like me , it's still a bug, nevertheless .. and probably outta have an ErrorDocument for the 502 error suggesting to close browser, clear cache , if the problem persists.. among other possible solutions..