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ingard's avatar
ingard
Icon for Nimbostratus rankNimbostratus
May 02, 2017

Reselect a specific backend based on initial response

Hi I'm trying to select a different backend and retry the same request based on the response from the initially selected backend. Basically the backend will either serve the request itself or respond with a 302 and put the host:port of another pool member (that has the content) in a header (X-TRANSCODE-REDIRECT-HOST). I put the following code together based on a few different examples I found on here, but it doesnt appear to work. At least the retry that I expected to happen never reaches the new pool member.

 

when CLIENT_ACCEPTED { 
    set retries 0
    set debug 5
}

when HTTP_REQUEST { 
  if { $retries == 0 } { 
    set request [HTTP::request]
  }
  if { $debug > 4 } { log local0. "HTTP_REQUEST - Retries : $retries - Request: $request" } 
}

when LB_SELECTED { 
  if { $retries == 0 } { 
     Log LB pool/server selection 
    if { $debug > 0 } { log local0. "Retries : $retries - Server Selected : [LB::server pool] [LB::server addr]:[LB::server port]" } 
  } else { 
     Reselect LB node if retries > 0
    if { $debug > 0 } { log local0. "Retries : $retries. wanted host/port = $wantedhost / $wantedport" }
    LB::reselect pool pool_media_transcoding $wantedhost $wantedport  

     Log LB pool/server selection 
    if { $debug > 0 } { log local0. "Retries : $retries - Server Selected : [LB::server pool] [LB::server addr]:[LB::server port]" } 
  } 
  if { $debug > 4 } { log local0. "LB_SELECTED - Retries : $retries - Request: $request" } 
} 

when HTTP_RESPONSE {
  if { [HTTP::status] eq 302 && $retries == 0 } {
    if {[HTTP::header X-TRANSCODE-REDIRECT-HOST] eq ""}{
      if { $debug > 0 } { log local0. "We got 302 from backend, but no X-TRANSCODE-REDIRECT-HOST header set" }
    } else {
      set wantedhost [lindex [split [HTTP::header X-TRANSCODE-REDIRECT-HOST] ":"] 0]
      set wantedport [lindex [split [HTTP::header X-TRANSCODE-REDIRECT-HOST] ":"] 1]
      if { $debug > 0 } { log local0. "We got 302 from backend. It wants us to redirect to $wantedhost : $wantedport" }
      incr retries
      HTTP::retry "$request" 
    }
  }
}
devops
iRules
LTM

3 Replies

  • JG's avatar
    JG
    Icon for Cumulonimbus rankCumulonimbus
    May 03, 2017

    The syntax does not seem to be right for this:

    LB::reselect pool pool_media_transcoding $wantedhost $wantedport

    . According to the manual, the syntax is:

    LB::reselect pool  member

    . Perhaps you meant to use the following instead:

    LB::reselect node

    .

  • ingard's avatar
    ingard
    Icon for Nimbostratus rankNimbostratus
    May 03, 2017

    It works with the change suggested by Jie, but I'm now seeing that the rule logs running through LB_SELECTED twice:

    May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : HTTP_REQUEST - Retries : 0 - Request: GET /segment/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJtZDUiOiJlZWYyMjAyZjg2ZGNjMDM0MmZiMjQ4ODExMTlkZjRlYyIsInVzZXJuYW1lIjoiZmF6ZXJtaW50ODIifQ.rNIkeMsXJfjPh7dlr1XkmY5uhRKuWeEz-4AcjIxRZqo/SD/segment000.ts HTTP/1.1  Host: domain.com  User-Agent: curl/7.46.0  Accept: */*  X-Forwarded-For: 1.2.3.4  jx_scheme: https
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : when LB_SELECTED : Retries : 0 - Server Selected : /Common/pool_media_transcoding 10.0.70.110:8105
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : Retries : 0 - Server Selected : /Common/pool_media_transcoding 10.0.70.110:8105
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : 1.2.3.4:20343: Server IP:port: 10.0.70.110:8105
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : We got 302 from backend. It wants us to redirect to 10.0.70.110 : 8106
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : HTTP_REQUEST - Retries : 1 - Request: GET /segment/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJtZDUiOiJlZWYyMjAyZjg2ZGNjMDM0MmZiMjQ4ODExMTlkZjRlYyIsInVzZXJuYW1lIjoiZmF6ZXJtaW50ODIifQ.rNIkeMsXJfjPh7dlr1XkmY5uhRKuWeEz-4AcjIxRZqo/SD/segment000.ts HTTP/1.1  Host: domain.com  User-Agent: curl/7.46.0  Accept: */*  X-Forwarded-For: 1.2.3.4  jx_scheme: https
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : when LB_SELECTED : Retries : 1 - Server Selected : /Common/pool_media_transcoding 10.0.70.110:8105
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : Retries : 1. wanted host/port = 10.0.70.110:8106
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : Retries : 1 - Server Selected :  10.0.70.110:8106
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : when LB_SELECTED : Retries : 1 - Server Selected :  10.0.70.110:8106
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : Retries : 1. wanted host/port = 10.0.70.110:8106
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : Retries : 1 - Server Selected :  10.0.70.110:8106
May  3 13:00:01 big-7 info tmm2[5109]: Rule /Common/irule_transcoder : 1.2.3.4:20343: Server IP:port: 10.0.70.110:8106
  • JG's avatar
    JG
    Icon for Cumulonimbus rankCumulonimbus
    May 04, 2017

    OK see two modified events:

    when CLIENT_ACCEPTED {
    set retries 0
    set re-selected 0
    set debug 5
}

when LB_SELECTED {
    if { $re-selected == 1 } {
        set re-selected 0
        return;
    }

    if { $retries == 0 } {
         Log LB pool/server selection
        if { $debug > 0 } { log local0. "Retries : $retries - Server Selected : [LB::server pool] [LB::server addr]:[LB::server port]" }
    } else {
         Reselect LB node if retries > 0
        if { $debug > 0 } { log local0. "Retries : $retries. wanted host/port = $wantedhost / $wantedport" }
        set re-selected 1
        LB::reselect pool pool_media_transcoding $wantedhost $wantedport

         Log LB pool/server selection
        if { $debug > 0 } { log local0. "Retries : $retries - Server Selected : [LB::server pool] [LB::server addr]:[LB::server port]" }
    }
    if { $debug > 4 } { log local0. "LB_SELECTED - Retries : $retries - Request: $request" }
}