topic Re: HTTP probe issue with expect regex string in Application Networking

HTTP probe issue with expect regex string

stevens_jj — Tue, 27 Sep 2011 18:10:35 GMT

Hello,

We have a simple cgi status page setup to poll a background service and return a "PASS" or "FAIL" as output. I've setup an HTTP probe to look for the "PASS" to determine application health. The issue appears to be that the expect regex is searching the HEADER but not the BODY of the web page. I can successfully match on any string in the header, but never on anything in the body.

Here is what the web page returns if you telnet to it:

HTTP/1.1 200 OK

Date: Thu, 22 Sep 2011 22:45:07 GMT

Server: Apache/2.0.59 HP-UX_Apache-based_Web_Server (Unix) DAV/2

Content-Length: 4

Connection: close

Content-Type: text/plain; charset=iso-8859-1

PASS

Here is my probe:

probe http JOE-TEST-CS

interval 45

passdetect interval 30

receive 30

request method get url /cgi-bin/ERMS-PREP-statusRepo.cgi

expect status 0 999

open 20

expect regex "PASS"

Here is the output of the show probe:

ACE1/euhr-test-ace2# sh probe JOE-TEST-CS detail

probe : JOE-TEST-CS

type : HTTP

state : ACTIVE

description :

----------------------------------------------

port : 80 address : 0.0.0.0 addr type : -

interval : 45 pass intvl : 30 pass count : 3

fail count: 3 recv timeout: 30

http method : GET

http url : /cgi-bin/ERMS-PREP-statusRepo.cgi

conn termination : GRACEFUL

expect offset : 0 , open timeout : 20

expect regex : PASS

send data : -

--------------------- probe results --------------------

probe association probed-address probes failed passed health

------------------- ---------------+----------+----------+----------+-------

serverfarm : JOE-TEST-PROBE-CS

real : EUHRTDM50.APP[0]

192.168.73.71 2 2 0 FAILED

Socket state : CLOSED

No. Passed states : 0 No. Failed states : 1

No. Probes skipped : 0 Last status code : 200

No. Out of Sockets : 0 No. Internal error: 0

Last disconnect err : User defined Reg-Exp was not found in Host Response

Last probe time : Thu Sep 22 15:00:36 2011

Last fail time : Thu Sep 22 15:00:36 2011

Last active time : Thu Sep 22 09:40:19 2011

If I replace the expect regex "PASS" with anything from the HEADER it succeeds!

Any thoughts?

HTTP probe issue with expect regex string

Kristopher Martinez — Tue, 27 Sep 2011 18:23:50 GMT

Joseph,

Does the server response contain the "content-length" header? This is required for expect regex and hash to function.

If this is a static page besides the PASS/FAIL variable, you could configure the ACE to hash the page. The ACE will generate a hash value of the page and if that hash value changes, the ACE will consider the probe failed.

http://www.cisco.com/en/US/docs/interfaces_modules/services_modules/ace/vA4_1_0/configuration/slb/guide/probe.html#wp1031557

Regards

Kris

HTTP probe issue with expect regex string

stevens_jj — Tue, 27 Sep 2011 19:18:49 GMT

If you look at the first part of my post - the "Content-Length: 4" header is in the header. I've tried the hash, but the same problem makes this bad as well since it is only hashing the header and NOT the body.

HTTP probe issue with expect regex string

Kristopher Martinez — Tue, 27 Sep 2011 20:21:07 GMT

Sorry, I missed it. The content-length in your request is 4. I think this may be the issue. I created a basic HTML page that says PASS in the body and my server is returning a content-length of 224 when I fetch the page. Here is my HTML request:

GET /index.html

http-equiv="Content-Type">

Probe

PASS

Here are my headers that I received:

(Status-Line) HTTP/1.1 200 OK

Content-Length 224

Content-Type text/html

Last-Modified Tue, 27 Sep 2011 12:05:00 GMT

Accept-Ranges bytes

Etag "8cca60aed7dcc1:41f"

Server Microsoft-IIS/6.0

Date Tue, 27 Sep 2011 12:25:59 GMT

What version of code are you running on your ACE? I can also look to see if there are any known issues.

Kris

Re: HTTP probe issue with expect regex string

stevens_jj — Tue, 27 Sep 2011 21:09:59 GMT

I'm not really sure what the Content-Length is supposed to be set at. I've done a ton of searching and its something like the number of octets of the body, which means nothing to me. I tried setting it to 224 like you have, but still fails.

I've even set it to 1024 and it still fails to find anything in the body. It still finds HEADER strings perfectly. Its as though it sees the header as the body.

Ace ver A2(3.4)

HTTP probe issue with expect regex string

Ahmad Basel Jaber — Wed, 28 Sep 2011 13:30:29 GMT

Hi Joseph,

Can you get sniffer traces from the server while the ACE is probing it? When you mentioned that you are telneting to the server, were you GETting /cgi-bin/ERMS-PREP-statusRepo.cgi to get the HTTP200 Ok message you provided?

Best regards,

Ahmad

HTTP probe issue with expect regex string

stevens_jj — Wed, 28 Sep 2011 16:00:32 GMT

I did the following to capture the output:

telnet server 80

GET /cgi-bin/ERMS-PREP-statusRepo.cgi HTTP/1.0

I'll grab a packet capture right now.

Re: HTTP probe issue with expect regex string

stevens_jj — Wed, 28 Sep 2011 18:42:46 GMT

I think we figured it out.

Had to do with a Cached response coming from Apache. Looks like by adding the client header Cache-Control: max-age=0, it forces Apache to send the new response every time.