WebSphere Administration: Using Thin Administration Client

Most people assume that in order to run WAS admin scripts, you need to have full WAS installation available on the client machine. This is not correct. Starting with WAS 6.1, it is possible to use the so-called administration thin client instead.

The thin client has many benefits:

  • The client consists of only two jars approximately 33MB in size, so you can set it up anywhere. With the traditional wsadmin client, you have to get WAS installed on your machine just so you can run wsadmin scripts. This is especially tedious if you have to deal with multiple versions of WebSphere products (and most large organizations have WAS versions in parallel). With the thin client you can just copy the two jars from an existing WAS installation onto a client machine. The only catch is that IBM JDK (or, more precisely, a JDK containing IBM security provider -- on Sun and HP-UX WAS actually comes with the Sun JDK) is still required. You can copy it from an existing install as well (I hope it doesn't violate any licensing terms).
  • Since the client's size is so small, you can add it to your version control or to your Maven repository. This makes the build more repeatable for developers (your build does include deploying to the application server and running tests against it, doesn't it?).
  • The shell script to run the thin client could be easily customized. For example, you may want to add some Java classes to wsadmin classpath. This will make it possible to invoke these classes from your wsadmin scripts. Or you may want to use a more modern jython version for your scripts. In fact IBM does't supply a shell script with the thin client, they just provide an example .

You'll need to make sure that you update your client jars whenever the server installation is upgraded.

Oh, and if you're using WebSphere ESB/Process Server and want to utilize some of WESB-specific admin tasks (available from AdminTask object), you're out of luck; the thin client will not support those.

This post is part of the series on WebSphere Application Server administration. Please subscribe to our blog if you'd like to receive updates.

Note: We offer professional services in the area of WebSphere architecture, implementation and operations. If you're looking for help with any of these tasks, please let us know.

ClassNotFoundException: A List of Dumb Things to Check

You deploy a new version of your application into production environment, hit the application’s URL and get a 500 error with a long error stack and nasty “java.lang.ClassNotFoundException” in bold at the top.

“Class Not Found” exceptions could be quite tricky to troubleshoot because of the complexity of Java Web applications and application servers they run on. An average web application nowadays comes bundled with dozens of jar file (and probably thousands of classes). An average application server’s classpath is many pages long. Not to mention separately deployed libraries containing jar files shared by a group of applications. There should be little surprise that it is quite common for all these different jars and classloaders to clash with each other, get out of sync or become otherwise corrupt and mis-configured.

The list below represents a subset of all the possible causes of “ClassNotFoundException”. Hopefully this list could serve as a starting point for attacking the problem. The list was inspired by A List of Dumb Things to Check.

  • To start, determine a type of the offending class. Is it a an application class, a third-party library class, a class provided by the application server or a JDK class? Determine the jar file that should contain the class. Determine where that jar should be located on the file system. Is it part of application installation, application server installation or some shared library installation? You may need to search for the class within multiple jars. Here is the command to do it (source): find . <del>name *.jar -print -exec jar -tvf {} ; | awk '/YOURSEARCHSTRING/ || /jar/ {print} ' (note-it won’t search within EAR and WAR files)
  • Does the jar that’s supposed to contain the class exist on the file system?
  • Are you able to “unjar” the jar using jar -xvf? Does the jar indeed contain the package and class in question?
  • Check the version of the jar if you can’t find the class there. To determine the version, look at the jar’s MANIFEST.MF. Usually (but, unfortunately, not always) you will find some version information there. You can also compare the file size with the “baseline”.
  • Does the account that the application server’s JVM was started with have read access to the jar? An application server usually runs under some sort of a system account. The jar might have been copied to the file system using a personal account from a different group.
  • Have all application jars been updated during deployment? Are all the jars (including shared libraries) at the right version? Manual deployment process is quite common, so missing to update a jar is always a possibility.
  • Is the class in question packaged with the application (e.g., under WEB-INF/lib) and being loaded by one of the parent classloaders? Most application servers utilize a classloader hierarchy where WAR file’s classloader is a child of EAR classloader which in turn is a child of the system (JVM) classloader. Parent classloaders can’t go down to request a class from a child classloader. The problem occurs if, for example, some jars were moved to a shared library but they still depend on classes packaged with the application.
    In order to diagnose this situation, you’ll need to have a good understanding of your application server’s classloader hierarchy. Here is the information for WebSphere and here is the WebLogic documentation on classloaders.
  • Is any of the jars packaged with the application also present on any of the parent classloader’s classpath? Running different versions of the same jar or library can cause all kinds of issues, including ClassNotFoundException. Some app servers allow overriding default classloader behavior so that the jars packaged with the application are loaded first. This could fix the problem.
  • If the jar with the class in question is part of a shared library (as opposed to packaged with the application), check if this library was made available to the application via the classloader configuration. For example, WebSphere configuration involves setting up a separate classloader for the library and explicitly associating it with the application.
  • Is the version and patch level of the application server correct? Does it match your development environment? Look at the detailed version information for all the different components of your app servers and also get a list of installed patches. E.g., for WebSphere run versionInfo -long command.
  • Is the application server running under the right JDK? E.g., check if the server startup script relies on JAVA_HOME and see which JDK the JAVA_HOME points to.
  • If the application runs in a cluster, does the problem occur on all nodes or just on some? Are you trying to troubleshoot the problem on the right node?
  • If the classname is driven from a string, either in java source or some other file, have you spelled the class name correctly? (Steve Loughran)

Once again, this is by no means a complete list. If anybody wants to contribute, please add a comment below and I’ll update the post.

Creating Ant Targets in Python with PAnt 2.0

We've just released a new version of PAnt, a tool for developing build scripts in python. The key new feature of PAnt 2.0 is the ability to create Ant targets directly from python. This allows for completely getting rid of Ant XML files and for developing build scripts entirely in Python.

Here is an example:
@target(unless="prop.name", depends=ptarget1)
def p_target2():
"""Python project ptarget2"""
ant.echo("echo ptarget2")

You can find more details about creating targets from PAnt here.

PAnt 1.5 is Released

This is a major update to our popular python Ant wrapper.

Notable changes in this release:

  • Support for positional (as opposed to named) arguments, e.g., “pant.echo(‘message’)”.
  • Support for lists to express repeating elements.
  • Support for “ant_” prefix to avoid conflicts with python keywords.

More information is available from PAnt project page

Please subscribe to our feed or follow us on twitter to continue receiving updates about PAnt – new version is coming shortly.

Eliminate the Need to Redeploy Your Web Files

Some application servers require that location of the development workspace has to be different from the location of the deployed application. For example, you can easily point Tomcat to the root of your Web application using “docBase” of the “Context” element. But you’re out of luck with WebSphere Application Server (WAS). You have to go through a separate application update process (using admin console or Rational Application Developer tooling) to synchronize your deployed application with the workspace. In my view, this update (a.k.a. “deployment”) step should never be required in a local development environment. It is one thing to have to deploy to a test or a production environment that consists of multiple servers that are segregated from the machine hosting the build artifacts. But in a situation when both the code and the application server are sitting on the same machine, the deployment step is redundant. We should be able to simply tell the app server where the code is and it can then do whatever is needed to load the code into JVM.

Luckily, we can get pretty close to this vision with a few very simple (and free) tools.

In my previous post I explained how to enable dynamic class reloading for WebSphere Application Server and avoid having to deploy your Java changes altogether. But what about changes to JSPs and other non-Java resources? How can we synchronize the directory used by the application server with the development workspace?

Turns out, there is an Eclipse plugin that does exactly that. It’s Filesync plugin developed by Andrei Loskutov.

As the name implies, the plugin automatically synchronizes workspace directories with external directories by doing one-way copy of changed files. It allows to specify multiple directory pairs and also to define include/exclude patterns and even use variable substitution.

To enable automatic updates of JSPs in the deployed application directory all you need to do is to define a folder pair that links web root in your workspace with the location of the exploded WAS directory in WAS (usually located under profile_root/installedApps/cell_name/app_name.ear/app_name.war).

With WAS you need to watch for static “<%@ include %>” directives in your JSPs. WAS will not reload included files unless you also update including JSP. A workaround here is to turn everything into “jsp:include” actions or use JSTL’s “c:import”. There might be a slight performance penalty for doing that but improved productivity is well worth it.

You can use Filesync plugin to synchronize your class files as well. This provides an alternative to the resource link-based approach that I described in the previous post. I still like using resource links better because they can be defined using Eclipse variables which makes it easier to share the configuration within a team. As far as I can tell, with Filesync you have to use absolute paths.

Here’s how the filesync configuration screen looks like:
Filesync configuration

Another good use of Filesync is to pull jar files from an external directory. Projects typically have a repository-like location where all third-party jars are checked-in (or it could be a full-blown Maven repository). You can easily add an external jar to your classpath in Eclipse. But how to put it under “WEB-INF/lib” where it needs to end up for the application server? With filesync it can be done easily by adding yet another folder pair.

In short, Filesync allows you to assemble your application “on the fly” without having to run an external build process. It also completely eliminates the need to explicitly update deployed applications.

Instantly Redeploy Your Classes to WebSphere Application Server

Any developer wants to see the code changes instantaneously reflected in the application server.
However, when using WebSphere Application Server (WAS), developers usually have to go through the process of deploying an application to the server. Even though the deployment support is integrated into Rational Application Developer (RAD) or Eclipse WTP, it still introduces delays and impedes productivity. Not to mention that Eclipse WTP does not actually support WAS 6.1 runtimes, only 6.0.

This is unfortunate because actually WAS 6.1 has good support for dynamic reloading. With dynamic reloading turned on, WAS monitors changes on the file system and automatically reloads the module (i.e., all classes loaded by the module’s classloader) when it detects a change. The reloading is almost instantaneous for simple modules. For complex modules with a lot of classes or initialization logic the reloading step could take a little bit of time but it is still faster than redeploying an entire application (you should check out Java Rebel if you want a truly instantaneous deployment).

With dynamic reloading all we need to do in order to make our changes available to the server is to update class files in the location where the deployed application resides. This is especially straightforward for web application and classes under WEB-INF/classes since WAS always explodes web application archives during deployment. In case of jar files (say the ones under WEB-INF/lib) the situation is a more complicated.

Unfortunately, the location of the deployed application is usually different from the workspace where a developer makes changes. By default, deployed binaries are located under profile_root/installedApps/cell_name. While this location can be changed, the directory structure will still be somewhat different from how code is organized in the workspace.

We could write a simple Ant script to copy changes, but this again introduces a special “pseudo-deployment” step. It would be nice if we could simply make a change in Eclipse, save it and let dynamic reloading kick in without any extra steps.

Turns out that it is quite possible to make WAS and Eclipse behave this way.

First, let’s configure WAS:

  • Log in to WAS admin console and make sure that “Run in development mode” is checked for your sever. This is the default for standalone installations.
  • Deploy your application to WAS using WAS admin console.
  • For convenience, you may want to specify a non-standard location for application binaries during installation to shorten the path, e.g., “was_installed_apps”. This step is optional.
  • Go to “Enterprise applications/your_app/Class loading and update detection”.
  • Make sure that “reload classes” is checked.
  • Set reload interval to some reasonable number, say “3”. By default it’s set to “0” which means “never”. IBM recommends 3 seconds as an optimal interval, although I’ve been using 1 second without any issues (for relatively small modules though).
  • Stop and start the application.

Now let’s configure Eclipse. We will have to create a resource link pointing to the deployed application and configure the project to compile classes to the deployed location.

  • Go to “Java Build Path” of the project. Click on “Browse” next to “Default output folder”.
  • Click “Create New Folder…”, “Advanced”, check “Link to folder in the file system”.
  • Click on “Browse” and locate the root of the exploded WAR file in the deployed application location. For example, for application “HelloWorldWeb” the path will be “profile_root/installedApps/cell_name/HelloWorldWeb.ear/HelloWorldWeb.war”. Give the link a meaningful name, e.g., “deployment”. Note: if you share .project and .classpath files with other developers, use Eclipse variables instead of the absolute path.
  • Click OK. This will create a resource link that you can use to specify the output folder.
  • Change the output folder to point to “project_name/link_name/WEB_INF/classes”, e.g., “HelloWorldWeb/deployment/WEB-INF/classes”. Click OK.
  • Eclipse will recompile your project.
  • From this point forward any class change will trigger dynamic reloading on the server.
  • The resource link is also available in your package explorer, so you can browse and edit the deployed files. You need to be careful if you want to edit JSPs or other files that way as they will be overridden by the next full re-deployment.

This techniques takes care of class files only. Dynamic reloading of JSP files is a different story.

Note: This has been tested only with Eclipse 3.4 and WAS 6.1 and on modules with a relatively small code base. I’d be curious to know how effective this approach is for large modules.

This post is part of the series on WebSphere Application Server administration. Please subscribe to our blog if you’d like to receive updates.

Note: We offer professional services in the area of WebSphere architecture, implementation and operations. If you’re looking for help with any of these tasks, please let us know.

WebSphere Administration: Setting Heap Size

Setting maximum heap size and changing other JVM parameters is a fairly common administration task. JVM configuration might be changing quite often during application development, usually as a result of performance testing.

Typically JVM parameters have to be updated for all application servers in a cell or at least for application servers that belong to a particular cluster.

Conveniently, WebSphere Application Server (WAS) supports updating JVM parameters using its administration APIs, specifically, AdminConfig object. This is illustrated by the script below.

import sys

Change JVM heap size for all application servers in a cell
# New heap size is passed as a parameter to the script

# Get the string with config ids of all serves
# Iterate over all servers - config ids are separated by \n 
for server_confid in server_confids.split("\n"):
    server_type=AdminConfig.showAttribute(server_confid, "serverType")
    # we're changing the heap size for application servers - we want to exclude node agents, etc.
    if server_type == "APPLICATION_SERVER":
        server_name=AdminConfig.showAttribute(server_confid, "name")
        # this is the query to get JavaVirtualMachine configuration object for a particular server
        jvm_path="/Server:%s/JavaProcessDef:/JavaVirtualMachine:/" % server_name
        # "modify" accepts  a list of lists - each list contains name and value (odd choice I must say, why not use tuples?)
        AdminConfig.modify(jvm_confid, [["maximumHeapSize", max_heap_size]])

# Commit our changes to the repository        

This post is part of the series on WebSphere Application Server administration. Please subscribe to our blog if you'd like to receive updates.

Note: We offer professional services in the area of WebSphere architecture, implementation and operations. If you're looking for help with any of these tasks, please let us know.

Dynamic Ant Tasks without Setters

Ant uses reflection to pass data from XML to the Java class that implement an Ant task. For every attribute in XML, you have to define a setter in the Java task’s class.

This works fine most of the time, however, in some cases there could be a need for a dynamic list of attributes. For example a task can pass attribute values to some external tool that has its own set of parameters that you don’t want to hardcode in Ant. Or you may simply like the flexibility of using dynamic attributes as opposed to predefined setters.

In order to implement dynamic attributes, first you need to override “maybeConfigure” method in your Ant task and have it do nothing:

public void maybeConfigure() throws BuildException {

Then in your “execute” method you can access the map of attributes (that represents all attributes set in XML) as follows:

RuntimeConfigurable configurator= getRuntimeConfigurableWrapper();
Map attributes=configurator.getAttributeMap();
String attr1=(String)attributes.get("attr1");

Note that in this case Ant does not do property substitution (for ${}), so you would need to explicitly invoke project.replaceProperties for each attribute value.

WebSphere Administration: Finding Cluster Members

There are many instances when it is necessary to find members (servers) that constitute a cluster. For example, to script starting and stopping an application, we need to know names of servers and nodes where the application is installed. Or we may want to restart all members of a cluster after some configuration change.

As always, this is easy to do when you know what you're doing. A query-like activity in WAS environment usually heavily relies on AdminConfig object. Our example is no exception:

import sys

List application servers that belong to a particular cluster
Cluster name is passed as a parameter to the script

# Get configID of the cluster
cluster_conf_id = AdminConfig.getid("/ServerCluster:"+cluster_name )
if not cluster_conf_id:
    raise "Cluster %s does not exist!" % cluster_name

# Get confids of the cluster members
member_conf_ids = AdminConfig.showAttribute(cluster_conf_id, "members")
# AdminConfig returns the list in [], get rid of the brackets
member_conf_ids = member_conf_ids[1:-1]
print "Cluster %s has following members:" % cluster_name  
# split by space
for member_conf_id in member_conf_ids.split():
    # Obtain server name and node name
    member_name=AdminConfig.showAttribute(member_conf_id, "memberName")
    node_name=AdminConfig.showAttribute(member_conf_id, "nodeName")
    print node_name+"/"+member_name

Now we can do a lot of useful things with node_name and member_name variables; for example, we can try to get an MBean of this server and check its state. Or we can attempt to restart it. I will cover this in one of the future posts.

This post is part of the series on WebSphere Application Server administration. Please subscribe to this blog if you'd like to receive updates.

WebSphere Administration: How to Force Node Synchronization

It is often desirable to "push" configuration changes to nodes in the cell without having to wait for the periodic node sync process to kick in. This becomes a requirement if you want to run some kind of automated testing as part of your configuration/deployment process (which is a very good practice). For example, you may have a build process which runs HTTPUnit tests immediately after the change.

In this case, you really don't want to rely on any artificial "sleeps" and delays in your script, so triggering synchronization programmatically is the best option.

This is actually quite simple to accomplish, as illustrated by the following script:

Sync configuration changes with nodes

# Commit changes to the configuration repository 

# Obtain deployment manager MBean

# "syncActiveNodes" can only be run on the deployment manager's MBean, 
# it will fail in standalone environment
if dm:
    print "Synchronizing configuration repository with nodes. Please wait..."
    # Force sync with all currently active nodes
    nodes=AdminControl.invoke(dm, "syncActiveNodes", "true")
    print "The following nodes have been synchronized: "+str(nodes)
    print "Standalone server, no nodes to sync"

This post is part of the series on WebSphere Application Server administration. Please subscribe to this blog if you'd like to receive updates.

WebSphere Administration: AdminControl vs AdminConfig

AdminContol and AdminConfig are two key scripting objects that any WAS administrator must know by heart.

The objects are available from wsadmin WAS administration tool.

AdminConfig provides an interface to the WAS configuration repository available under profile_root/config. All AdminConfig services are provided by the Deployment Manager (assuming you're connecting remotely); there is no dependency on node agents.

AdminControl provides an interface to JMX managed beans (MBeans) in your WAS environment. In general, MBeans are only available for the resources that are running. For example, if an application server is down, the corresponding MBean will not be available.

AdminConfig and AdminContol could complement each other nicely, especially when you need to find out the status of "things" in a WAS cell. To illustrate the point, here is a simple script that prints the status of all application servers within a cell:

List all application servers in a cell and print their status (up or down)

# Get the string with config ids of all serves
#Iterate over all servers - config ids are separated by \n 
for server_confid in server_confids.split("\n"):
    server_type=AdminConfig.showAttribute(server_confid, "serverType")
    # we are only interested in application servers
    if server_type == "APPLICATION_SERVER":
        # obtain the name of the server
        server_name=AdminConfig.showAttribute(server_confid, "name")
        print "Checking the state of the server %s of type %s" % (server_name, server_type) 
        #Now we can try to get the mbean of the server. We could've used AdminConfig.getObjectName() as 
        #a shortcut, but for the sake of the example we'll use AdminControl explicitly
        # Query to search for mbeans - note the wildcard at the end to match the rest of mbean parameters
        # Note that we're simplifying a little bit since we're ignoring node names -
        # server names may not be unique within cell  
        server_query="type=Server,name=%s,*" % server_name
        server_mbean=AdminControl.queryNames( server_query )
        # AdminContol returns None if there is no running mbean for this server
        if server_mbean:
            print "Server is up"
            print "Server is down!"

This post is part of the series on WebSphere Application Server administration. Please subscribe to this blog if you'd like to receive updates.

Using Jython 2.2.1 with WSAdmin Tool

In one of the previous posts I complained that wsadmin tool (which is the main WebSphere Application Server administration tool) still relies on Jython 2.1, which is quite old.

The issue became critical when I realized that jython automatically re-compiles classes compiled with a different jython version. In my case, I was using Jython 2.2 for my Ant scripts and Jython 2.1 for wsadmin scripts. Some of the code was shared. This led to the situation of concurrent builds stepping on each other by dynamically re-compiling classes with different jython versions. The error looked something like that:

File "<string>", line 5, in ?
java.lang.ArrayIndexOutOfBoundsException: -4
at org.python.core.imp.createFromPyClass(Unknown Source)

Bugs like that are always fun to troubleshoot.

Going back to 2.1 was not an option for me since I use closures and “new classes” in quite a few places. So I tried putting jython 2.2.1 on wsadmin classpath and it worked without a hitch with thin wsadmin client. All my of wsadmin scripts work without a problem.

Here is a sample wsadmin.bat file that I use. This file utilizes thin client jars. Note how in line 85 my jython.jar (which is jython 2.2.1) is added to the classpath so it would override jython packages supplied with WAS.

One possible downside of this approach is running into issues with IBM support in case if you need to open a PMR related to wsadmin scripting.