PH41417: LOAD BALANCER INCORRECTLY MARKS SERVER AS COLLOCATED

APAR status

• Closed as program error.

Error description

• Collocated is set to yes when a 'server set' command is issued
  to multiple servers and one of the servers is collocated.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:  IBM WebSphere Application Server Edge Load  *
  *                  Balancer for IPv4 and IPv6 users            *
  ****************************************************************
  * PROBLEM DESCRIPTION: LB may not forward to a server. LB      *
  *                      reports indicate packets forwarded to   *
  *                      the server.                             *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  If you have a collocated server and issue a 'server set'
  command with the collocated server and another server at the
  same time, LB incorrectly flags both servers as collocated.
  When the non-collocated server is selected to receive traffic,
  LB forwards the packet to the collocated server instead of the
  selected server.
  Example problematic 'server set' commands (assume 1.2.3.4 is a
  collocated server):
  dscontrol server set cluster@port@1.2.3.4+1.1.1.1 weight 5
  dscontrol server set @@ weight 5
  

Problem conclusion

• Internal code for the 'server set' command checked if the
  address of the server existed on the local LB machine. If the
  address was found, the code set the collocated flag to true.
  This causes LB to forward the packet as if the server is
  collocated so the traffic is not sent to the selected server.
  
  Code corrected to eliminate setting collocated flag on
  non-collocated servers.
  
  Fix levels:
     8.5.5.21
     9.0.5.10
  

Temporary fix

• Two workarounds are available to prevent this problem:
  
  1) Do not issue compound 'server set' commands when using a
  collocated servers. For example, instead of "dscontrol server
  set cluster@port@1.2.3.4+1.1.1.1 weight 5", issue the commands
  separately: "dscontrol server set cluster@port@1.2.3.4 weight
  5" and "dscontrol server set cluster@port@1.1.1.1 weight 5"
  
  2) After setting server values, issue additional commands to
  ensure collocated flag set correctly. For example:
  dscontrol server set cluster@port@1.2.3.4 collocated yes
  dscontrol server set cluster@port@1.1.1.1 collocated no
  

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  WS EDGE LB IPV4

• Fixed component ID

  5724H8812

Applicable component levels