Debugging Health Monitors on BigIP 9

We experienced that a lot of our health monitors didnt work on our BigIP boxes, and we sure as hell didnt see why.
After surfing a bit on the magical devcentral.f5.com, we found out that the BigIP only recieves the first 5120 bytes of a fetched result in a health monitor.

This is how to debug with curl:
curl -H 'Host: virtualhost.webserver1.com' -D - "webserver1.com80/index.html?q=bladdibla" | head -c 5120

Now you can ex. grep for a string to see if your healthcheck will do fine on a webserver (within the 5120 first bytes)

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Show headers for a http request using curl(with specified virtualhost)

Normally when I want to see what the hell a webserver returns for any given request i would use telnet

wrky ~ # telnet webserver01 80
Trying 123.123.123.4...
Connected to webserver01.example.org.
Escape character is '^]'.
GET / HTTP/1.0

HTTP/1.1 301 Moved Permanently
Date: Mon, 13 Oct 2008 11:58:12 GMT
Server: Apache/1.3.34
Location: http://localhost/index.html
Content-Length: 100
Connection: close
Content-Type: text/html; charset=utf-8

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But wait, why not do it the more sane way; using curl with the dump headers trigger:

wrky # curl -D - webserver01.example.org
HTTP/1.1 301 Moved Permanently
Date: Mon, 13 Oct 2008 11:58:28 GMT
Server: Apache/1.3.34
Location: http://webserver01.example.org/index.html
Content-Length: 111
Connection: close
Content-Type: text/html; charset=utf-8

This item has moved here.

And if, like me, you have several virtualhosts (vhosts) on the same webserver; add the host header with the -H header trigger;

wrky ~ # curl -H 'host: picsearch.example.org' -D - webserver01.example.org
HTTP/1.1 200 OK
Date: Mon, 13 Oct 2008 12:05:49 GMT
Server: Apache/1.3.34
Content-Length: 6171
Connection: close
Content-Type: text/html; charset=utf-8

This item has moved here.

Be aware that the -H does NOT stand for Host, but Header – you need to put the word “Host:” before the virtualhost address. Somehing like -H ‘Host: www.cnn.com’

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