Rolf Schaufelberger wrote:
Am 24.10.2009 um 12:13 schrieb André Warnier:
Rolf Schaufelberger wrote:
It always has googleads as referer with a very long refer string and
what das the 502 status mean?
http://lmgtfy.com?q=http+status+502
Ok, I can read what's written there, but what does it mean ?
I still have no idea, what leads to that error. As far as I understood
this, my backend server send something else but no HTTP message to the
frontend server.
But why?
Rolf,
502 Bad Gateway
The server was acting as a gateway or proxy and received an invalid
response from the downstream server.
It means that your front-end server received this request ("GET /"),
from some client, which apparently was at the time displaying a page
which itself had been obtained from the long link that you see in the
message. (It does not mean that the request itself came from a Google
server; it just means that on some page of Google somewhere, there is a
link that points to your site, and that someone clicked on it).
Now, we don't know what the configuration of your front-end and back-end
servers are, nor what is exactly proxied to your back-end server when
the front-end server receives a request for "/".
But the error code 502 that is in the log (see description above) seems
to indicate that your front-end server passed this request somehow to a
back-end server, and that it received an invalid response from the
back-end server.
Why that is, is also not known to us, and quite impossible to figure out
with the information you provided.
If I had to make a guess, I would say that the problem has nothing to do
with this request in particular, and that your front-end server is just
configured with too many children or threads, compared to the physical
memory it really has. So when many requests come in and it tries to
fork more children/threads to handle them, it runs out of memory.
Reducing MaxClients may be a first option.
About reproducing this access with LWP, sure :
lwp-request -m GET http://your-server-name/
but that is not going to tell you much.