IBM WebSphere Application Server Fails With java.lang.UnknownHostException

Resolving The Problem

The java.lang.UnknownHostException typically occurs when one of the following is true.

1) TCP/IP is not started on the server.
2) The Fully Qualified Domain Name (FQDN), which consists of the hostName.domainName (i.e. server.ibm.com) listed in CFGTCP Option 12 is not being resolved to a valid IP address properly.
3) The FQDN specified in the WebSphere Application Server profile configuration is not being resolved to a valid IP address properly.

First, verify that TCP/IP is started on the IBM i by running the STRTCP command or checking NETSTAT Option 10. Then, attempt to PING the IBM i server using its host name as defined in the TCP/IP configuration. You can run the CFGTCP command and select Option 12 to determine the full qualified domain name (FQDN) defined for the system. The FQDN is defined as the host name plus the domain name (i.e. AS400.ibm.com). If your host name search priority is set to *LOCAL, verify the FQDN (host.domain) name is set to a valid, active TCP interface on the system in the local host table in CFGTCP Option 10.

You can verify the host name being used by your WebSphere Application Server profile by viewing the /QIBM/UserData/WebSphere/AppServer/<version>/<edition>/profiles/<profileName>/config/cells/<cellName>/nodes/<nodeName>/serverindex.xml file.

i.e. /qibm/userdata/websphere/appserver/v85/express/profiles/default/conig/cells/AS400_default/nodes/AS400_default/serverindex.xml

When displaying this file, you would want to look at the endPoint configuration for your WAS profile. Locate one of the endPoint lines which are similar to the following.

<endPoint xmi:id="EndPoint_1183122129640" host="AS400.ibm.com" port="2867"/>

In this example, the FQDN used by the WebSphere Application Serve profile is AS400.ibm.com. You would need to ensure this FQDN is being properly resolved to a valid IP address either through the local host table or through your DNS.

If the FQDN needs to be changed for your WAS profile's configuration, you can do this by following the instructions in the IBM Technical Document:
How To Change The Host Name For An IBM WebSphere Application Server Full Profile

You can test to see if the FQDN configured for the server resolves to an IP address successfully by using the Java program IPTest located in the app_server_root/bin directory. Where app_server_root is the following:

/QIBM/ProdData/WebSphere/AppServer/<Version>/<Edition>/bin

<Version> = V6, V61, V7, V8, V85, V9

<Edition> = Express, Base, ND

This example was run from QShell:

   $

The values returned by IPTest (and usually used by WebSphere) come from the TCP configuration. You can look at the TCP configuration using the CFGTCP command. Option 12 shows the FQDN (host.domiain) WebSphere is using. It also shows if a DNS is being used (HOSTSCHPTY=*REMOTE) or if the IBM i host table is being used (HOSTSCHPTY=*LOCAL). The IBM i host table can be viewed and changed with Option 10. The TCP interfaces (TCP/IP addresses) are under Option 1. When displaying the TCP interfaces, press F11 on to view the status of each interface.