Thursday, February 26, 2009

Do Not Step On Other's Feet [WLST scripting Best Practices (Part-2)]

This post is a continuation of my previous post - in a series of posts about WLST scripting best practices. When using WLST script for performing configuration changes always check whether someone else is making changes. WebLogic support configuration changes using many methods but not limited to:
  • Administration Console
  • Interactive WLST
  • WLST SCripts
  • JMX
  • Ant Scripts
  • 3rd Party Tools
So it is always better to check whether someone else is making changes while you are ready to start a change session. WebLogic Server will allow only one change session at a time no matter which one of the above methods you use for configuration management. Especially environments with multiple administrators the best practice is to have individual logins for each administrator so that you can have more controlled environment. If you are interested in configuration auditing to find out who is responsible for what, see this post.

Use the Configuration Manager to find out information about existing change sessions. You can find out whether someone else had already started a change session, if so who is making changes, are there any unactivated changed, if so what changes are unactivated etc. from the configuration manager. The following example illustrates a code snippet which checks for existing sessions using configuration manager:


...
### Get the Configuration Manager and check for existing session
cfgManager = getConfigManager()
try:
cfgManager.getChanges()
print '===> Someone else is making changes'
except:
print '===> No one else is making changes'
...


The following example illustrates a code snippet which checks for the number of unactivated changes using configuration manager:


...
### Get the Configuration Manager and check for existing session
cfgManager = getConfigManager()
try:
cfgManager.getChanges()
print '===> Someone else is making changes'
noOfChanges = cfgManager.getUnactivatedChanges().__len__()
print 'There are ' + noOfChanges + ' unactivated pending changes in the current edit session'
except:
print '===> No one else is making changes'
...

The above code snippet may work only if you are the user who is making the changes. The following example illustrates a code snippet which checks and prints the user who is currently making changes using configuration manager:


...
### Get the Configuration Manager and check for existing session
cfgManager = getConfigManager()
try:
cfgManager.getChanges()
print '===> User ' + configmanager.getCurrentEditor() + ' is making changes'
except:
print '===> No one else is making changes'
...


The following example is a complete script which checks for an existing session and if one doesn't exists then it will create a new managed server by starting a new session. If a session already exists then it will simply display that information and will exit.



from weblogic.management.mbeanservers.edit import NotEditorException

### CreateMgdServer.py
### Define all the requried variable
username = 'braman'
password = 'weblogic'
url = 't3://localhost:7001'
mgdServerName = 'mgdserver1'
resourceType = 'Server'
listenAddress = 'egmgd1'
listenPort = 2001

### Connect to the Administration Server
connect(username, password, url)

### Get the Configuration Manager
cfgManager = getConfigManager()
try:
cfgManager.getChanges()
print '===> Currently there is a Session'
if cfgManager.isEditor() == true:
### You are making changes!!!
print '===> Looks like you started that session'
print '===> You can check the console for any pending changes'
print '===> Try rerunning this script after you release or commit the pending changes'
exit()

except NotEditorException, e:
if cfgManager.getCurrentEditor() is None:
### No session
pass
else:
### Someone else is making changes
userWithSession = cfgManager.getCurrentEditor().replace(' ', '')
print '===> Currently there is a Session'
print '===> User \"' +userWithSession+'\" is making the changes'
print '===> Wait until \"' +userWithSession+'\" complete the current session'
exit()
pass
except Exception:
### Other Errors
print '===> Error, see log for more info'
exit()


### Start a change session
edit()
startEdit()

### Create the Managed Server
create(mgdServerName, resourceType)
cd('/Servers/' + mgdServerName)
cmo.setListenPort(listenPort)
cmo.setListenAddress(listenAddress)
print '===> Created Managed Server - ' + mgdServerName

### Activate the changes
save()
activate()

### Disconnect from the Administration Server
disconnect()
exit()

To explain some tricky parts of the above script:

This is line of code is used to import the exception class
from weblogic.management.mbeanservers.edit import NotEditorException

To check whether you are holding on to a session currently you can use the following method on the configuration manager
cfgManager.isEditor()

To get the user who is currently making changes you use the getCurrentEditor method on the configuration manager
cfgManager.getCurrentEditor()

To get rid of all the white spaces you can use a replace method from the string class (this is Jython)
userWithSession = cfgManager.getCurrentEditor().replace(' ', '')


The above example works if you don't have a managed server named egmdg1. But if you already have a managed server in your domain with the same name then the script will fail with the following error:

weblogic.descriptor.BeanAlreadyExistsException: Bean already exists

You can handle that situation in couple of different ways. I shall continue on how to tackle that in my next post.

WLST-BP-2 Check for existing session before you start one

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