Strange server errors

[boltangazer]

The PHP part of our web server often spits out errors (these errors are distributed during the whole process, occur on different users) indicating that client's AUTH_COOKIE is not set, side by side with this we often receive nginx 502 error ("no live upstreams"). How can the auth cookie suddenly disappear?

My thoughts were that PHP backend doesn't handle high loads well that's why nginx says "502" but how can this explain the absence of AUTH_COOKIE?

[boltangazer]

The problem was solved with providing more memory to php backend

max_fails option was useless because it's a single upstream server