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

Variable Definitions In The Preamble [WLST scripting Best Practices (Part-1)]

With WLST becoming popular among WebLogic Administrator, there is an unsaid need to discuss the best practices with respect to WLST scripting. I am being asked to share information about WLST like an introductory/101 post. But I decided to start a series of post which might help WebLogic Administrators with some of the must follow best practices rather than writing some introductory post which might duplicate the documentation. For WLST documentation see here.

The common steps involved in a WLST script that is used to configure WebLogic Server are as follows:

1. Connect to server
2. Navigate to the respective location (MBean)
3. Modify the required properties
4. If more configuration needs to be modified continue Step-2
5. Else disconnect
6. Exit

The first of the series of best practices in authoring a WLST script is to define all the required variables at the beginning before connecting to the server. That way if any modifications must be done in the future it will be as easy as changing the variables defined at the beginning of the script. In the coming posts, I will talk about more of other best practices like writing a reusable WLST script, consuming information from the environment variables, exception handling, defensive scripting, avoiding to hard code critical information like username, password, url etc.

The usual variables are the username, password, url, resource names, attribute values etc. The following is an example of a script that defines all the required values as script variables which can avoid hardcoding and will also facilitate simple way to modify them in the future if required.

#CreateServer.py
#Define all the requried variable
username = 'system'
password = 'weblogic'
url = 't3://egAdm:7001'
serverName = 'mgdserver1'
listenAddress = 'egmgd1'
listenPort = '2001'

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

#Start a change session
edit()
startEdit()

#Create the Managed Server
create(serverName, 'Server')
cd('/Servers/' + serverName')
cmo.setListenPort(listenPort)
cmo.setListenAddress(listenAddress)

#Activate the changes
save()
activate()

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

The above script may not be authored using all the best practices now. But I will eventually build on the same example of creating a new Managed Server in my subsequent posts to address the other best practices as well. My next post will talk about how to check for existing change session before you start one with WLST.

WLST-BP-1 Define all the variables in the preamble