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8.4.1.2: Servlet Redirector Problems

8.4.1.2: Servlet Redirector Problems

Servlet redirectors are used to separate the HTTP server from the WebSphere Application Server. There are different types of redirectors:

  • Thick - servlet redirector resides on the same machine as WebSphere Administrative Server.
  • Thin - servlet redirector runs on a separate machine from the WebSphere Administrative Server.
    A thin servlet redirector is useful in network configurations where the HTTP server is outside a firewall but WebSphere Application Server is behind a firewall, or where WebSphere Application Server is located in the DMZ, a machine located between two firewalls.
  • Note:  If Web Server, App server and the Server handling servlet requests all reside on the same machine, use OSE - Open Servlet Engine, instead of a servlet redirector

Key features

The key features of servlet redirectors are:

  1. Use IIOP (Internet Inter-Orb Protocol) for communication
  2. Are initialized by copying the queues.properties, rules.properties, and vhosts.properties files from the WebSphere Application Server machine to the servlet redirector machine.
  3. Use the following ports to transfer the properties files:
    • port 900 - bootstrap port
    • port 9000 - name services port
    • redirector listener port
  4. Require the receiving RemoteSRP bean to be running on the WebSphere Application Server
  5. When servlet redirectors are running, beside the ports previously listed, they also require the following, additional ports:
    • Application Server listener port
    • Admin server nanny listener port
    • Thick servlet redirectors also require repository database connection ports

Typical Problems

Typical problems with servlet redirectors are:

  1. Error 404 - URL not found appears on browser when accessing a servlet.
    The trace log for the HHTP server contains entry:
    Failure while locating a vhost for <server>
    This error may occur if:
    • The short (myserver) and fully qualified (myserver.mydomain.com) hostnames of the HTTP server are not in the virtual host alias list.
    • A port other than the standard port 80 is used and that port is not in the virtual host alias list.
  2. CORBA.COMM_FAILURE appears when running the thin servlet redirector. This error may occur if:
    • Syntax error exists in batch file
    • Hostname/port number is not in DNS or hosts.properties file on servlet redirector machine
    • Hostname/port number is not in DNS or hosts.properties file on WebSphere Application Server machine
    • -ListenerPort parameter value is not unique
    • Syntax error in -ListenerPort parameter
  3. Unable to initialize threads: (null) error when running the batch/script file to configure the plugin files. This error may occur if:
    • Some JDK other than the IBM supported JDK is in the CLASSPATH ahead of the supported JDK. To resolve this problem, install the supported IBM JDK, and change the PATH and CLASSPATH to point to it first.
    • PATH does not point to java.exe.
  4. When starting servlet redirector with batch/script file, get error message Error locating Remote SRP Home - Attribute Not Set. This error occurs because:
    • RemoteSRP bean was not added and started on WebSphere Application Server
  5. Do not use servlet redirectors if you must:
    • enable security on your thin servlet redirector machine
    • provide the real Web browser on your thin servlet redirector machine
    • use the Network Address Translation feature of firewalls so that the internal address of WebSphere Application Server is not available outside the firewall

Reminder:  Generally errors occur configuring the thin servlet redirector function because required configuration files are missing. A thin servlet redirector machine requires the following shell script files (on UNIX platforms), or bat files on Windows NT as well as the iiopredirector.xml file to enable the servlet redirector function.

servlet redirector files

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