variable getting reset during irule execution

Chris,

 

 

I'm far from an expert at variables in iRules so my only suggestion would be creating a global variable, rather than a local variable.

 

 

See this article about global variables: https://devcentral.f5.com/tech-tips/articles/irules-101-03-variables.UV2gXzd5g08

 

 

So, in your example it would be something like: "set ::host_num=(digit after /serv)" and then referenced thus: "if { $::host_num != 0 }"

 

 

Hope this helps,

 

N

A global variable would be global to the whole box (ie. everyone), so that wouldn't work. Are you saying that the check for $host_num in the LB_SELECTED event fails? Does it crash the iRule?

Try this to test and please report the results:

when HTTP_REQUEST {
log local0. "here"
set host_num 0
}
when LB_SELECTED {
log local0. "here"
if { [info exists host_num] } {
log local0. "host_num exists"
} else {
log local0. "host_num does not exist"
}
}

I used your test code and host_num does exist. I don't ever see a host_num does not exist in my logs.

 

 

But my problem occurs in my irule like so:

 

 when HTTP_REQUEST { 
log local0. "here" 
set host_num 0 
if { [string tolower $uri] starts_with "/serv" } { 
      log local0. "prefix redirect initiated" 
      if { [string tolower $uri] matches_regex {serv[\d]+} } { 
               scan $uri /serv%d host_num 
               set path "/" 
               log local0. "uri match found $host_num" 
      } else { 
               scan $uri /serv%d%s host_num path 
               log local0. "uri match not found assert $host_num" 
      } 
      HTTP::uri $path 
} 

when LB_SELECTED { 
log local0. "LB here" 
if { $host_num != 0 } {
    redirect the request to the appropriate member 
           switch $host_num { 
                    1 {
                          LB::reselect pool SERV member 10.10.10.2 
                          log local0. "prefix redirect selecting /serv1" 
                        }
 } } 

 

 

 

My problem occurs when LB_SELECTED executes. For some reason $host_num is always being reset to 0.

 

 

It's almost like any user who tries to use the prefix redirect to select a specific server, will get the host_num variable set, but before the LB_SELECT function executes the session/connection is cleared and they get host_num = 0 or something.

 

 

Any ideas?

 

 

I'm a little curious about your if conditional:

if { [string tolower $uri] matches_regex {serv[\d]+} } {

You're saying that if there's a number after the /serv URI, set the host_name and the path. But then in the else condition, you have this: scan $uri /serv%d%s host_num path. This assumes there's a number after the /serv URI, followed by a path. I would think that host_num wouldn't be set in this condition, considering the /serv URI doesn't have a number after it.

Can you try this minor variation:

when HTTP_REQUEST {
log local0. "here"
set host_num 0
set path "/"
if { [string tolower [HTTP::uri]] starts_with "/serv" } {
log local0. "prefix redirect initiated"
if { [string tolower [HTTP::uri]] matches_regex {serv[\d]+} } {
scan [string tolower [HTTP::uri]] /serv%d%s host_num path
log local0. "uri match found: $host_num"
} else {
scan [string tolower [HTTP::uri]] /serv%s path
}
log local0. "path = $path"
HTTP::uri $path
}
}
when LB_SELECTED {
log local0. "here"
if { [info exists host_num] } {
log local0. "host_num exists: $host_num"
if { $host_num != 0 } {
switch $host_num {
1 {
LB::reselect pool local-pool member 10.70.0.2
log local0. "prefix redirect selecting /serv1"
}
}
}
} else {
log local0. "host_num does not exist"
}
}

Thanks for the response. I made the changes and every time it checks for host_num existance in the LB_SELECTED event, hust_num is 0.

 

 

I get the following in my logs on one request to example.com/serv1

 

Thu Apr 4 16:15:42 EDT 2013 Rule clewdev-new-prefix-redirect : host_num exists: 0

 

Thu Apr 4 16:15:41 EDT 2013 Rule clewdev-new-prefix-redirect : host_num exists: 0

 

Thu Apr 4 16:15:41 EDT 2013 Rule clewdev-new-prefix-redirect : host_num exists: 0

 

Thu Apr 4 16:15:41 EDT 2013 Rule clewdev-new-prefix-redirect : host_num exists: 0

 

Thu Apr 4 16:15:41 EDT 2013 Rule clewdev-new-prefix-redirect : host_num exists: 0

 

Thu Apr 4 16:15:41 EDT 2013 Rule clewdev-new-prefix-redirect : host_num exists: 0

 

Thu Apr 4 16:15:41 EDT 2013 Rule clewdev-new-prefix-redirect : path = /

 

Thu Apr 4 16:15:41 EDT 2013 Rule clewdev-new-prefix-redirect : uri match found: 2

 

 

Like I said, this irule worked flawlessly for 4 or 5 years and then one day I threw in a new iRule that had some chunking/http1.0 changes(which has been removed for over a week) and its been messed up since then.

 

 

Thanks again

 

Can you share your entire iRule?

 

 

Have you or can you reboot the BIG-IP (or do a bigstart restart)?

Here is the entire rule with IP's changed etc. But this is the meat of it.

when HTTP_REQUEST { 
set uri [HTTP::uri]
set host_num 0
set req_cookie [HTTP::cookie "DEVPERSIST"]

if { [string tolower $uri] starts_with "/serv" } {


if { [string tolower $uri] matches_regex {serv[\d]+} } {
scan $uri /serv%d host_num
set path "/"
} else {
scan $uri /serv%d%s host_num path
}

snip the host prefix from the URI
HTTP::uri $path
                


remove the cookie if it's there
if { [HTTP::cookie exists DEVPERSIST] } {
HTTP::cookie remove DEVPERSIST
}
                
              

}
}

when LB_SELECTED {
if { $host_num != 0 } {
                log local0. "hostnum here $host_num"
redirect the request to the appropriate member
switch $host_num {
1 {
LB::reselect pool DEV member 10.10.10.2:7085
}

2 {
LB::reselect pool DEV member 10.10.10.3:8080
}

}
}
}

when HTTP_RESPONSE {
if { $host_num != 0 } {
HTTP::header insert Set-Cookie "DEVPERSIST=[HTTP::cookie DEVPERSIST]; Path=/"
            log local0. "hostnum here $host_num"
}
}

I haven't rebooted the F5 yet since it serves about 30 different high usage web applications. But I can talk to our sys admins about doing so at some point.

Fundamentally I don't see anything wrong with the logic. I'm still curious about your else condition though, given that there won't be a number after /serv if this condition is met. I would recommend a bigstart restart on the assumption that NOTHING else has changed other than applying and then removing some iRule logic.

Can you also try this variation of your rule:

when HTTP_REQUEST { 
set host_num 0
set req_cookie [HTTP::cookie "DEVPERSIST"]
set path "/"
if { [string tolower [HTTP::uri]] starts_with "/serv" } {
log local0. "starts with /serv"
if { [string tolower [HTTP::uri]] matches_regex {/serv[\d]+} } {
log local0. "match_regex"
scan [string tolower [HTTP::uri]] /serv%d%s host_num path
log local0. "host_num = $host_num"
log local0. "path = $path"
} else {
log local0. "not match_regex"
scan [string tolower [HTTP::uri]] /serv%s path
log local0. "path = $path"
}
snip the host prefix from the URI
HTTP::uri $path
remove the cookie if it's there
if { [HTTP::cookie exists DEVPERSIST] } {
HTTP::cookie remove DEVPERSIST
}
}
}
when LB_SELECTED {
if { $host_num != 0 } {
log local0. "hostnum here $host_num"
redirect the request to the appropriate member
switch $host_num {
1 {
log local0. "selecting member 1"
LB::reselect pool DEV member 10.10.10.2:7085
}
2 {
log local0. "selecting member 2"
LB::reselect pool DEV member 10.10.10.3:8080
}
}
} else {
log local0. "hostnum = 0"
}
}
when HTTP_RESPONSE {
if { $host_num != 0 } {
HTTP::header insert Set-Cookie "DEVPERSIST=[HTTP::cookie DEVPERSIST]; Path=/"
log local0. "hostnum here $host_num"
} else {
log local0. "hostnum = 0"
}

Thanks Kevin. I've scheduled a restart for Monday, so hopefully that solves it.

 

 

I'm not sure what that else logic is for either. The irule was written by my predecessor.

Kevin "A global variable would be global to the whole box (ie. everyone), so that wouldn't work." - doh! I missed that key point about global variables. Back to the Variables 101 guide me thinks. Thanks

 

 

N