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HTTP Health Monitor in LTM

Bhavik_1402
Nimbostratus
Nimbostratus

Hi Folks,

 

We've following requirement to configure HTTP health monitor and this is what we need to implement.

 

Type Send Receive

HTTP GET /Sample/healthchecksimple HTTP/1.1 200|OK

HTTP GET /Sample123/servlet/fcs/ping HTTP/1.1 200|System Current Time

HTTP GET /sample456/test-alive HTTP/1.1 200|OK

HTTP GET /Sample789/manager?query=monitoring HTTP/1.1 302

HTTP GET /Sample459/monitoring/healthcheck HTTP/1.1 200|OK

HTTP GET /Sample324/servlet/fcs/ping HTTP/1.1 200|System Current Time

HTTP GET /Sample438/monitoring/healthcheck HTTP/1.1 200|OK

HTTP GET /healthcheck HTTP/1.1 200|OK

 

Would like to know if this is correct syntax for Send and Receive string or need to modify? we need to associate this to pool.

 

 

 

12 REPLIES 12

boneyard
MVP
MVP

this knowledge article explain how to build send strings quite well: https://support.f5.com/csp/article/K2167

 

so you first send will end up something like this, where the Host part it optional

 

GET /Sample/healthchecksimple HTTP/1.1\r\nHost: host.domain.com\r\nConnection: Close\r\n\r\n

as for your receive what are trying to get exactly? HTTP/1.1 200 or OK ? specially those seem a bit odd, as they can easily cause a false up if OK is somewhere further.

Thanks Boneyard,

 

I am not sure as we are still in build phase but as per the documentation it should be as below.

 

Receive String - HTTP/1.1 200|OK

Receive String - HTTP/1.1 200|System Current Time

 

is there any meaning of | between 200 and OK ?

and for Send String

 

GET /Sample/healthchecksimple HTTP/1.1\r\nHost: \r\n\r\n

 

would be the correct syntax?

boneyard
MVP
MVP

Receive String - which documentation did you use for that? the | means or, it is either 200 or OK. which you probably don't want. if you are just looking for HTTP return code 200 then HTTP/1.1 200 OK is fine. for the others it is more difficult to judge without actual output.

 

this comes mainly down to how your application responds, perform a regular request to it and check the response to see what a good match would be.

 

Send String - if you dont want to add the hostname then drop that whole part, so like this:

 

GET /Sample/healthchecksimple HTTP/1.1\r\nConnection: Close\r\n\r\n

though formally this isn't allowed for a HTTP/1.1 request. it also depends on the way your application is setup, it might require a hostname or wont respond correctly without one.

 

best is to test this with curl or such from a system to see what happens with the different variants.

The documentation is provided by Application Vendor and I've tested as below. The Receive string is "ok".

 

do I need to mentioned in Receive string as "200 OK" or only "OK" ? is it case sensitive?

 

config # curl -k http://X.X.X.X:8445/Sample/healthchecksimple

Bad Request

This combination of host and port requires TLS.

config # curl -k https://X.X.X.X:8445/Sample/healthchecksimple

ok

 

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

I'm struggling to configure Send string. do i need to select HTTP or HTTP monitor?

 

I've tried few syntax but still failing.

 

GET /Sample/healthchecksimple HTTP/1.1\r\nHost: \r\n\r\n

 

GET /Sample/healthchecksimple HTTP/1.1\r\nHost: xyz.ab.com\r\n\r\n

 

GET /Sample/healthchecksimple HTTP/1.1\r\nHost: xyz.ab.com\r\nConnection: Close\r\n\r\n

 

is it mandatory to use xyz.ab.com after Host: for HTTP 1.1 ? any suggestions?

 

The documentation is provided by Application Vendor and I've tested as below. The Receive string is "ok".

 

do I need to mentioned in Receive string as "200 OK" or only "OK" ? is it case sensitive?

 

config # curl -k http://X.X.X.X:8445/Sample/healthchecksimple

Bad Request

This combination of host and port requires TLS.

config # curl -k https://X.X.X.X:8445/Sample/healthchecksimple

ok

 

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

I'm struggling to configure Send string. do i need to select HTTP or HTTP monitor?

 

I've tried few syntax but still failing.

 

GET /Sample/healthchecksimple HTTP/1.1\r\nHost: \r\n\r\n

 

GET /Sample/healthchecksimple HTTP/1.1\r\nHost: xyz.ab.com\r\n\r\n

 

GET /Sample/healthchecksimple HTTP/1.1\r\nHost: xyz.ab.com\r\nConnection: Close\r\n\r\n

 

is it mandatory to use xyz.ab.com after Host: for HTTP 1.1 ? any suggestions?

 

please try with curl -v -k ...

 

that shows header information

 

if the content reply is ok, then your receive string is just that: ok

 

but be careful because is there is ok in the header it will also trigger

I removed the TLS and SSL outputs. Does it mean I should also add "HTTP/1.1 200 ok" in receive string or only "ok" just to make sure it detects the correct string to keep the pool member up.

 

> GET /Sample/healthchecksimple HTTP/1.1

> Host: X.X.X.X:8445

> User-Agent: curl/7.47.1

> Accept: */*

>

< HTTP/1.1 200

< Content-Length: 2

< Date: Thu, 29 Apr 2021 17:59:20 GMT

<

* Connection #0 to host x.x.x.x left intact

ok[F5]config #

in this case just "ok" is fine.

 

just be careful that you don't take something which also occurs in the header like "on", which is a part of Content-Length.

Thank you so much boneyard, this really helps.

 

just last thing , in what cases we need to put "200 OK" as i have seen in some monitors so just wondering. does it mean receive string contains 200 as well ?

and for one the monitor the receive string mentioned as "HTTP/1.1 302" which is redirection but when i do curl then i see that it redirects but does not see any string similar to "ok" or something else.

 

how do i configure receive string to set as "302" so it marks up?

 

< HTTP/1.1 302

< Location: https://XXX.XXX.XXX/abc/xyz

< Content-Length: 0

 

well that usually is more focused on the first reponse line you see in the header

HTTP/1.1 200

this often is

HTTP/1.1 200 OK

and then the 200 OK makes sense, in your case there are several lines between the 200 and the ok (also lower case).