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8: Problem determination >
8.5: Identifying the problem >
8.5.2: Servlet redirector problems
8.5.2: 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 the Web server, application server and the server handling servlet requests
all reside on the same machine, use Open Servlet Engine(OSE), instead of a servlet redirector
Key features
The key features of servlet redirectors are:
- Use Internet Inter-Orb Protocol (IIOP) for communication
- Are initialized by copying the queues.properties, rules.properties,
and vhosts.properties files from the WebSphere Application Server machine to the servlet redirector machine.
- Use the following ports to transfer the properties files:
- port 900 - bootstrap port
- port 9000 - name services port
- redirector listener port
- Require the receiving RemoteSRP bean to be running on the WebSphere Application Server
- 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 with servlet redirectors are:
- 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) host names 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.
- CORBA.COMM_FAILURE appears when running the thin servlet redirector. This
error may occur if:
- Syntax error exists in batch file
- Host name/port number is not in DNS or hosts.properties file on servlet redirector
machine
- Host name/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
- Unable to initialize threads: (null) error when running the batch/script file
to configure the plug-in 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.
- 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
- 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.
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