Forum Discussion

Nimbostratus

Jan 31, 2023

Insert header when item added to ramcache

Haven't been in here for a looong time... :-7 Trying to store a header value received from pool member in a new header as that item is added to the ramcache (so it'll be present when that item is su...

application delivery

JRahm

Admin

Hi Hendel, I haven't done much with the cache in iRules, but your format for setting appears to be correct. That said, can you post a sanitized version of your iRule and whether you have any other iRules or policies that might be interfering? How are you validating that it is not working? Could use CACHE::trace to see if anything is at least being set by the system before hitting a tcpdump on the wire.

Hendel

Nimbostratus

Feb 07, 2023

There aren't any other rules or policies. I'd tried both insert and replace, but the logging in CACHE_RESPONSE never showed any effect from either of the UPDATE commands.

when CACHE_UPDATE {
  CACHE::header insert X-LTM-Cached $cache
  # CACHE::header replace Cache-Control $cache
}
when CACHE_RESPONSE {
  log local0. "[IP::client_addr] path:$path cache:$cache [CACHE::headers]"
}
when HTTP_REQUEST {
  set path [string tolower [HTTP::path]]
  if { !($path ends_with ".js") } {
    CACHE::disable
  } else {
      HTTP::uri [HTTP::path]
      CACHE::enable
  }
}
when HTTP_RESPONSE {
  set cache [HTTP::header value Cache-Control]
  HTTP::header replace Cache-Control public
}

JRahm
Admin
Feb 07, 2023
I updated the formatting to make it a little easier to read through...let me reach out internally to see if anyone has worked with the cache commands before, I'm not quite sure what the flow should be here.
John_Alam
Employee
Feb 08, 2023
Are you using the webacceleration profile: optimized-caching?

can you post any changes you may have made.

Can you include a log statement in the CACHE_UPDATE event so we can see if it is firing?

when CACHE_UPDATE { log local0. "Caching [HTTP::uri]" }

Thanks.
- John_Alam
  Employee
  Feb 08, 2023
  I did some quick testing.
  
  1) Your iRule does not work as is, the variable 'cache' is not passed from LTM Events to Cache events. So you will run into "variable not found" TCL errors. I excluded that variable to continue testing.
  
  2) I used the 'optimized-caching' profile which defaults to 'Minimum Object Size' of 0 bytes. I could not get the header to insert, or the CACHE_UPDATE to fire, until I increased that to 1 byte. It must be a bug of sorts.
  
  You can see the header inserted X-LTM-Cached: test. Note , i used a static value because as i mentioned, the variable was not transfered.
  
  One way to transfer variable is with iRule tables. Try passing from one event to another using a Table record.
  
  HTH.