cancel
Showing results for 
Search instead for 
Did you mean: 

https health monitor configured with only send strings but no receive strings - what it will check ?

Sarovani
Cirrostratus
Cirrostratus

Hi Team ,

 

If we have https health monitor configured with only send strings but no receive strings in it , what checks does it perform .

can you please explain with below configuration as an example .

 

Pool Member : 10.10.10.10 : 443

 

https Monitor

 

Send string :  GET /health\r\n

Receive string : ( not configured ) 

1 ACCEPTED SOLUTION

Per F5 documentation:

 

"Content check monitors are designed to determine whether a service is available and whether the server is serving the appropriate content."

 

Also in the same article, "You can also use the default null Receive String value [""] [in a content check monitor]. In this case, any content retrieved is considered a match." (Emphasis mine.)

 

In other words, without a receive string, a content check monitor satisfies only its first purpose - "to determine whether a service is available." To satisfy the second purpose of a content check monitor - "to determine if the server is serving the appropriate content" - you must include a Receive String with the appropriate content. This is by design, as F5 cannot possibly know what constitutes appropriate content for your application. We provide the monitor shell; you customize it for your application delivery needs.

View solution in original post

4 REPLIES 4

crodriguez
F5 Employee
F5 Employee

A content check monitor with no receive string is relatively powerless to assess application delivery health. In the case of your HTTPS monitor, for example, the system will establish a secure connection to the pool member, send the HTTP 0.9 GET request you provided in the Send String, and any response - including a 404 Not Found or other HTTP 500 error - is considered a successful response and the monitor will mark the pool member as available. As such, your monitor is not much more effective than a service check monitor and certainly not (necessarily) indicative of application delivery health.

 

Conventional wisdom is to use an appropriate receive string in a content check monitor.

ok so in that case the default https monitor in the F5 also not having receive string.So it's of no use right ? it is same as using tcp-443 monitor ? is that right .

Per F5 documentation:

 

"Content check monitors are designed to determine whether a service is available and whether the server is serving the appropriate content."

 

Also in the same article, "You can also use the default null Receive String value [""] [in a content check monitor]. In this case, any content retrieved is considered a match." (Emphasis mine.)

 

In other words, without a receive string, a content check monitor satisfies only its first purpose - "to determine whether a service is available." To satisfy the second purpose of a content check monitor - "to determine if the server is serving the appropriate content" - you must include a Receive String with the appropriate content. This is by design, as F5 cannot possibly know what constitutes appropriate content for your application. We provide the monitor shell; you customize it for your application delivery needs.

Sarovani
Cirrostratus
Cirrostratus

ok so in that case the default https monitor in the F5 also not having receive string.So it's of no use right ? it is same as using tcp-443 monitor ? is that right .