I bisected the bug to the frontal: the attached script capture the live TCP
connections from the frontal to the application server upon status 500
errors and I can confirm that the request body payload is missing from
these sessions so, the frontal did not send the bytes to the application
server.
Now, it could be that I do not receive the missing bytes on my frontal or
the frontal is dropping them. I can't reuse the same script because my
frontal's traffic is encrypted.
Is there a way to make uwsgi dump somewhere the decryption keys for an ssl
session so I could decrypt the associated traffic on the fly and dump the
traffic for later inspection when I see a 500 ?
Mathieu
Le mar. 12 mars 2019 à 11:14, mathieu lacage <[email protected]> a
écrit :
> Hi,
>
> My production servers are deployed as 4 uwsgi instances:
>
> front1 -> admin3+admin4
> front2 -> admin3+admin4
>
> front1/2 are load balanced at the DNS level and perform ssl termination
> with uwsgi and forward requests to admin3/4 by using an http subscription
> server. admin3/4 run my python application within a simple uwsgi master+5
> slaves.
>
> Before you ask: on all 4 servers,
> $ uwsgi --version
> 2.0.15-debian
>
> Recently, I became aware of a low-probability bug triggered by multiple
> customers across a wide range of access networks that happens when reading
> the body of my incoming POST HTTP requests at the application level.
>
> Here is a typical backtrace:
>
> Mar 09 08:32:10 admin3 uwsgi[8246]: admin-5 ERROR root timeout
> during read(2) on wsgi.input
> Traceback (most recent call last):
> File
> "/usr/local/lib/python2.7/dist-packages/webapp2.py", line 1535, in __call__
> rv =
> self.handle_exception(request, response, e)
> File
> "/usr/local/lib/python2.7/dist-packages/webapp2.py", line 1529, in __call__
> rv = self.router.dispatch(request,
> response)
> File
> "/usr/local/lib/python2.7/dist-packages/webapp2.py", line 1278, in
> default_dispatcher
> return
> route.handler_adapter(request, response)
> File
> "/usr/local/lib/python2.7/dist-packages/webapp2.py", line 1102, in __call__
> return handler.dispatch()
> File "admin2/BaseHandler.py", line
> 99, in dispatch
> self._do_dispatch(user)
> File "admin2/BaseHandler.py", line
> 327, in _do_dispatch
>
> self._begin_transaction(company_id, user)
> File "admin2/BaseRequestHandler.py",
> line 210, in _begin_transaction
> self._data = self.request.body
> File
> "/usr/lib/python2.7/dist-packages/webob/request.py", line 702, in body
> self.make_body_seekable() # we
> need this to have content_length
> File
> "/usr/lib/python2.7/dist-packages/webob/request.py", line 930, in
> make_body_seekable
> self.copy_body()
> File
> "/usr/lib/python2.7/dist-packages/webob/request.py", line 954, in copy_body
> data = input.read(min(todo, 65535))
> File
> "/usr/lib/python2.7/dist-packages/webob/request.py", line 1540, in readinto
> data = self.file.read(sz0)
> IOError: timeout during read(2) on
> wsgi.input
> Mar 09 08:32:10 admin3 admin[3875]: [uwsgi-body-read] Timeout reading 2
> bytes. Content-Length: 2 consumed: 0 left: 2
>
> Ok, I get this: my application is trying to read these damn 2 bytes but
> they are not in the wsgi input file so, uwsgi triggers the 4s (default
> value) socket timeout.
>
> Now, the issue here is that I'd like to figure out if these damn bytes
> were actually received on the application server and if not, where they got
> lost so I can blame someone else.
>
> Has anyone any idea on what I could do to debug/trace this further on my
> production infrastructure ? (clearly, logging all incoming traffic with
> tcpdump is not an option)
>
> Mathieu
> --
> Mathieu Lacage <[email protected]>
>
--
Mathieu Lacage <[email protected]>
import argparse
import os
import pcapy
import pypacker.ppcap
import pypacker.layer12.ethernet
import pypacker.layer3.ip
import pypacker.layer4.tcp
class Session:
def __init__(self):
self._packets = []
self._keep = False
def append(self, p):
self._packets.append(p)
@property
def length(self):
return len(self._packets)
def keep(self):
self._keep = True
def close(self, directory, k):
if self._keep:
filename = os.path.join(directory, '%s.pcap' % k)
print('keep %s' % filename)
with pypacker.ppcap.Writer(filename=filename, linktype=pypacker.ppcap.DLT_EN10MB) as pwriter:
for p in self._packets:
pwriter.write(p)
def main():
parser = argparse.ArgumentParser()
parser.add_argument('-i', '--interface', required=True)
parser.add_argument('-f', '--filter', default=None)
parser.add_argument('-o', '--output-directory', default=os.getcwd())
args = parser.parse_args()
sessions = {}
reader = pcapy.open_live(args.interface, 65536, 0, 1000)
if args.filter is not None:
reader.setfilter(args.filter)
def receive(header, packet):
eth = pypacker.layer12.ethernet.Ethernet(packet)
ip = eth[pypacker.layer3.ip.IP]
tcp = eth[pypacker.layer4.tcp.TCP]
a = (ip.src_s, tcp.sport)
b = (ip.dst_s, tcp.dport)
k = '-'.join(sorted([ip.src_s, ip.dst_s, str(tcp.sport), str(tcp.dport)]))
session = sessions.get(k)
if session is None:
session = Session()
sessions[k] = session
session.append(packet)
if tcp.body_bytes.startswith(b'HTTP/1.1 500'):
session.keep()
if tcp.flags & 0x0001:
# FIN
#print('close %s' % k)
#print(session.length)
session.close(args.output_directory, k)
del sessions[k]
reader.loop(0, receive)
main()
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