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yabbadabbadont
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PostPosted: Mon Aug 17, 2009 4:14 am    Post subject: One of the load balanced servers isn't configured correctly. Reply with quote

Every few times when I hit the "View your posts", or other shortcut links, I am prompted by firefox with the save file dialog instead of the page opening correctly. Since it has only started happening since today's down time, I'm guessing that one (or more) of the load balanced servers doesn't have the correct mime type set for php files.

Here is a screen shot to illustrate: http://omploader.org/vMjV6ag

This is awesome... I got the same problem when I hit the Submit button for this post... :lol:

See: http://omploader.org/vMjV6bA
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poly_poly-man
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PostPosted: Mon Aug 17, 2009 5:29 am    Post subject: Reply with quote

I've noticed konqueror giving "timeout" errors instantly quite a bit today.
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desultory
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PostPosted: Mon Aug 17, 2009 7:38 am    Post subject: Reply with quote

yabbadabbadont wrote:
Every few times when I hit the "View your posts", or other shortcut links, I am prompted by firefox with the save file dialog instead of the page opening correctly.
Are you browsing from behind a proxy? If you save the file, what are the contents? If you are encountering the same problem I have been the files should have 0 length.
yabbadabbadont wrote:
Since it has only started happening since today's down time, I'm guessing that one (or more) of the load balanced servers doesn't have the correct mime type set for php files.
This appears to be due to the load balancer itself, as both of the servers behind it seem to be working normally.

poly_poly-man wrote:
I've noticed konqueror giving "timeout" errors instantly quite a bit today.
This matches my testing with that browser.

If a solution proves elusive during the next day or so, we will probably, temporarily, fall back to a single front end server until we can test the balancing system more thoroughly.
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XavierMiller
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PostPosted: Mon Aug 17, 2009 7:46 am    Post subject: Reply with quote

Hello,

I am behind a proxy and I got "zero size reply" messages.
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yabbadabbadont
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PostPosted: Mon Aug 17, 2009 9:22 am    Post subject: Reply with quote

desultory wrote:
Are you browsing from behind a proxy? If you save the file, what are the contents? If you are encountering the same problem I have been the files should have 0 length.

Nope. Direct connection to the DSL modem with no proxy configured or running.

It hasn't happened the last few times I've hit the site, so it may have just been some sort of short term thing right after the downtime. I'll post back if I see it again.

Edit: Spoke too soon. It happened right after I posted this when I hit the "View your posts" link. Then it happened twice when I hit the edit button on this post. All three times the php file was zero bytes when saved.

Edit2: It happened when I hit Submit on the first edit... and three times when hitting the edit button to add this edit.... I'm going to just stick to the Ubuntu forums for a while I think. :lol:
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richard.scott
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PostPosted: Mon Aug 17, 2009 10:22 am    Post subject: Reply with quote

Hi,

I am also getting blank pages!
...I have to refresh each page about 3 times before I see its content.

I'm also behind a proxy of some kind.

However, if I VPN to home and the connect (bypassing the local proxy) then its really quick.

What technology is being used to do the load balancing?

edit: in the few min it took to type this message I then saw "Invalid Session" when I submitted it... not sure if its linked or not.

Rich
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bunder
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PostPosted: Mon Aug 17, 2009 11:00 am    Post subject: Reply with quote

i'm also getting blank pages behind my local squid proxy.
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atrus123
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PostPosted: Mon Aug 17, 2009 11:20 am    Post subject: Reply with quote

Blank pages ditto!
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PostPosted: Mon Aug 17, 2009 12:12 pm    Post subject: Reply with quote

yeah, I am getting lots and lots of timeouts for the last ~12h
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PostPosted: Mon Aug 17, 2009 1:59 pm    Post subject: Reply with quote

desultory wrote:
If a solution proves elusive during the next day or so, we will probably, temporarily, fall back to a single front end server until we can test the balancing system more thoroughly.
Had you thought of using DNS round-robin?
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krinn
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PostPosted: Mon Aug 17, 2009 3:17 pm    Post subject: Reply with quote

same problem here, didn't change a thing, and not using proxy... (but my isp should use one)
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mikegpitt
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PostPosted: Mon Aug 17, 2009 3:36 pm    Post subject: Reply with quote

Blank pages here also, both at work and at home. No proxy's...
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XavierMiller
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PostPosted: Mon Aug 17, 2009 3:44 pm    Post subject: Reply with quote

It's quite annoying... can't you test before to put directly under production, with a test environment?
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robbat2
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PostPosted: Mon Aug 17, 2009 5:44 pm    Post subject: Re: One of the load balanced servers isn't configured correc Reply with quote

yabbadabbadont wrote:
Every few times when I hit the "View your posts", or other shortcut links, I am prompted by firefox with the save file dialog instead of the page opening correctly. Since it has only started happening since today's down time, I'm guessing that one (or more) of the load balanced servers doesn't have the correct mime type set for php files.
The Apache configuration on the two servers is byte-for-byte identical. If you can reproduce the problem, I'd like to know what MIME type IS being sent with those pages.

desultory wrote:
This appears to be due to the load balancer itself, as both of the servers behind it seem to be working normally.
The load balancer is purely at a TCP level (IPVS). It does not proxy or even see the response packets.

poly_poly-man wrote:
Had you thought of using DNS round-robin?
DNS round-robin does not accurately balance the load, due to broken DNS resolvers sorting the results and returning the first one.

For anybody that can trigger it repeatedly, I need to know if any headers are sent with the empty page, or if the entire response is empty.

Also, if you explicitly want to hit one side of the system, there is the DNS entries for [url]forums-web1.gentoo.org[/url] and [url]forums-web2.gentoo.org[/url].
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bbgermany
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PostPosted: Mon Aug 17, 2009 6:12 pm    Post subject: Reply with quote

OK, i got a white page right now: http://forums.gentoo.org/viewtopic-t-788306.html

Sourcecode shows nothing. Not even the html tags. Just a white page. The size is 0KB according to the page information.

bb

EDIT: took me three tries to post this. Always got blank posting.php pages.
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XavierMiller
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PostPosted: Mon Aug 17, 2009 6:18 pm    Post subject: Reply with quote

Yep, this happens at ANY moment: read message, reply, send reply...

This is TOO ANNOYING... :roll:
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poly_poly-man
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PostPosted: Mon Aug 17, 2009 6:33 pm    Post subject: Reply with quote

firing up wireshark now.


EDIT: I'm getting a TCP DUP ACK, and then only outgoing tcp packets, then nothing. http://omploader.org/vMjYzag


Last edited by poly_poly-man on Mon Aug 17, 2009 6:37 pm; edited 1 time in total
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energyman76b
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PostPosted: Mon Aug 17, 2009 6:33 pm    Post subject: Reply with quote

get notification mail, click on link, 3 or 4 instead timeouts before the page loads. Posting something? 5 timeouts can happen.
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robbat2
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PostPosted: Mon Aug 17, 2009 8:15 pm    Post subject: Reply with quote

poly_poly-man wrote:
firing up wireshark now.
EDIT: I'm getting a TCP DUP ACK, and then only outgoing tcp packets, then nothing. http://omploader.org/vMjYzag
Can you make an actual tcpdump packet capture and email it to me please? robbat2@gentoo.org

Please trim it to just the TCP transaction that has the problem, no other traffic.
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robbat2
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PostPosted: Mon Aug 17, 2009 8:34 pm    Post subject: Reply with quote

I've dropped web2 back out for now, but still using the LB with just web1.

web2 is giving me a bunch of PAX errors :-(
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XavierMiller
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PostPosted: Tue Aug 18, 2009 6:56 am    Post subject: Reply with quote

Thank you for your work, robbat2!
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think4urs11
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PostPosted: Tue Aug 18, 2009 7:10 am    Post subject: Reply with quote

robbat2 wrote:
desultory wrote:
This appears to be due to the load balancer itself, as both of the servers behind it seem to be working normally.
The load balancer is purely at a TCP level (IPVS). It does not proxy or even see the response packets.

Issues with session stickyness (as i'm also discovering that bug right now with no proxy in between and working with https while writing this post)?
Is the LB configured to bind particiular clients (by ip, cookie, session-id) to a particiular backend server or is it just a 50:50 'splitter'?
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robbat2
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PostPosted: Tue Aug 18, 2009 7:57 am    Post subject: Reply with quote

Think4UrS11 wrote:
robbat2 wrote:
desultory wrote:
This appears to be due to the load balancer itself, as both of the servers behind it seem to be working normally.
The load balancer is purely at a TCP level (IPVS). It does not proxy or even see the response packets.

Issues with session stickyness (as i'm also discovering that bug right now with no proxy in between and working with https while writing this post)?
Is the LB configured to bind particiular clients (by ip, cookie, session-id) to a particiular backend server or is it just a 50:50 'splitter'?


Right now, only web1 is running on the LB. web2 has apache disabled, potentially until it gets a visit from the screwdriver fairy.
If you think you're seeing any persistence issues at all, that's impossible because there can't be any by definition. They would be other problems masquerading as persistence issues.

The configuration in general is a weighted least connections (wlc in IPVS) model, which approximates a 50:50 split in connection durations, not simply connection numbers. There is no persistence configured, and the database replication should be fast enough to carry your sessions over. If it does end up being more problematic, I can enable long-term persistence (so multiple connections take the same path if available) in the www LB side, at the cost of a large tracking table.

ASCII art of the new forums setup
Code:

Incoming HTTP connections:
--------------------------
X = crossbar switch.
GW = gateway to network.

                       /-> db1 --> web1
Client -> GW -> IPVS -*         X
                       \-> db2 --> web2
               
IPVS runs on BOTH database servers, one of which at a time has the (virtual) IP
for the forums.g.o entry. They communicate via VRRP to agree who is in charge.

Outgoing HTTP packets:
----------------------
webN ---> GW ---> client

Backend processing:
-------------------
web1 --> haproxy ---> db1
                  X
web2 --> haproxy ---> db2

haproxy runs on both web nodes. PHP connects on localhost to haproxy, and gets
an even 50:50 split between database servers. The database connections are
fully proxied.
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poly_poly-man
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PostPosted: Tue Aug 18, 2009 12:59 pm    Post subject: Reply with quote

and what exactly is squid doing installed and erroring on web2? seems like it would make more sense without squid... but then again I've never run a high-throughput server (I got 3 hits a day one time!).
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robbat2
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PostPosted: Tue Aug 18, 2009 5:47 pm    Post subject: Reply with quote

poly_poly-man wrote:
and what exactly is squid doing installed and erroring on web2? seems like it would make more sense without squid... but then again I've never run a high-throughput server (I got 3 hits a day one time!).

Squid is installed on both, but not yet enabled, it's for later, to cache the contents of non-static pages.
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