Live Application Mobility in AIX 6.1

Application Mobility using WPARs

The most popular innovation of IBM® AIX® 6.1 is arguably workload partitioning. Workload partitioning allows you to have fewer operating system images on your managed system, which is accomplished by allowing virtualization of operating system resources. Live Application Mobility is an important component of workload partitioning and provides for increased availability for workload partitions (WPARs). Simply put, it allows you to move WPARs from one logical partition (LPAR) to another while the WPARs are up and running. It provides automatic, policy-based relocation of workload between systems using WPARs. This article explores how and when to use Live Application Mobility and how to configure a system and its applications to run it.

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Ken Milberg, Writer/site expert

Ken Milberg is a technology writer and site expert for Techtarget.com and provides Linux technical information and support at Searchopensource.com. He is also a writer and technical editor for IBM Systems Magazine, Power Systems edition, and a frequent contributor of content for IBM developerWorks. He holds a bachelor's degree in computer and information science, as well as a master's degree in technology management from the University of Maryland University College. He is the founder and group leader of the N.Y. Metro POWER-AIX/Linux Users Group. Through the years, he has worked for both large and small organizations and has held diverse positions from CIO to senior AIX engineer. He is currently president and managing consultant for UNIX-Linux Solutions, is a PMI-certified Project Management Professional (PMP), an IBM Certified Advanced Technical Expert (CATE), and is also IBM SCon certified.



03 June 2008

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WPARs, LPARs, and Live Application Mobility

Among other benefits, WPARs allow you to deploy applications more quickly and requires far fewer dedicated hardware resources. In fact, unlike a logical partition (LPAR), no physical resources are actually required to build a WPAR. As most system administrators have come to realize, the biggest disadvantage of LPARs are maintaining multiple images, which goes along with possibly over-committing expensive hardware resources, such as CPU and RAM. In other words, while partitioning helps you consolidate and virtualize hardware within a single box, operating system virtualization through WPAR technology goes one step further and allows for an even more granular approach of resource management. It does this by allowing for the sharing of OS images and is clearly the most efficient use of CPU, RAM, and I/O resources.

Rather than a replacement for LPARs, WPARs are a compliment to them and allow one to further virtualize application workloads through operating system virtualization. WPARs also work very well with Role-Based Access Control (RBAC), which is another important innovation in AIX 6.1. So what does this have to do with Live Application Mobility?

Live Application Mobility allows you to relocate running WPARs from one LPAR to another. While Sun may have a similar concept with its zone-based strategy, it does not provide for a hot migration of running applications. Of all the UNIX®-based systems, only the IBM AIX OS has this important innovation. The way it works is that it uses features such as checkpointing to move the actual running partitions. The checkpoint saves and validates the status of the current application and then starts its back up on the other LPAR in this saved state. Do you still need High Availability solutions such as HACMP if you will be using this feature? Absolutely. It's important to make the distinction that Live Application Mobility provides for increased availability during scheduled outages, not unscheduled outages. One needs to actively use WPAR manager or the command line interface to initiate the movement of the WPARs; it is not automatic. Live Application Mobility is actually an optional feature that is enabled within the WPAR manager component. What's the difference between partition mobility and Live Application Mobility? Partition mobility is a feature of Power6™ that allows you to migrate entire AIX or Linux® LPARs from one physical server to another. It does not require AIX 6.1 or WPARs. This feature helps when scheduling downtime for entire frames.

If you need to take an entire managed system off-line, you can move its partitions to another server. It also allows you to balance workloads and resources by allowing you to move LPARs to different physical servers. Live Application Mobility is an innovation of AIX 6.1 alone and is a component of its WPAR strategy, allowing you to move workloads rather than entire partitions. The actual target WPARs can be a different server, though it doesn't have to be. It is more flexible, as you can use it on environments where you have a mixed physical architecture: Power5 and Power6. It moves applications away from systems that require scheduled downtime for maintenance. It can also be used to improve performance by moving workloads from stressed out servers to less overtaxed ones. Further, it can help provide energy savings by moving the workload around in such a way as to allow a physical server to literally sleep during non-peak periods. The table below shows some basic differences between Live Application Mobility and Partition Mobility.

Table 1. Differences between Live Application Mobility and Partition Mobility
TYPELive Application MobilityLive Partition Mobility
OSAIX 6.1Linux, AIX 5.3, AIX 6.1
HardwarePowerPC® 970, POWER4™, 5™, 6™Power6
GranularityWPARsLPARs

Live Application Mobility -- Configuration challenges

This section looks at how to configure Live Application Mobility.

There are two ways to configure Live Application Mobility. The first is by using the WPAR manager (part of the IBM System Director family) and the second is using the command line. IBM strongly suggests you use the WPAR manager, and having used both, I would say it's simpler and much more powerful to use the manager. Furthermore, it performs certain compatibility tests between both the source and global environments, which are just not provided from the command line. IBM goes as far as to say: "Using the WPAR manager is therefore the only recommended way to perform a WPAR relocation" (see Resources for a link). That was enough for me not to even consider demonstrating moving WPARs around using the command line; however, if you are so inclined to experiment, the command line tools include the following commands:

  • chkptwpar -- This is the command that creates a snapshot of all the tasks in a WPAR.
  • killwpar -- This command kills all tasks belonging to a paused WPAR.
  • restartwpar -- This command creates the workload partition from the checkpointable state.
  • resumewpar -- This command resumes execution of a paused or frozen WPAR.

The WPAR manager uses a browser-based interface that allows for the management of the WPARs from literally any platform. It is designed to manage WPARs and provides the enablement that allows one to use Live Application Mobility. It is also a licensed product, which means it costs money. It includes a centralized database consisting of DB2® with an agent that needs to be installed on each computer. This is very helpful because you do not need to log into the LPAR itself to actually create, configure, and enable Live Application Mobility. It also provides for policy-based mobility, which can significantly reduce your overall workload.

When planning for Live Application Mobility, it's important to start out by defining your reason behind relocating the WPARs. And once you understand the why behind your decision to relocate the WPARs, you'll also need to take into account the workloads on both the source and target system. It's one thing to use Live Application Mobility as a tool that will allow you to move an application off of an LPAR whose physical server needs maintenance for a couple of hours; it's another issue entirely to use this to improve application performance. When using it for the latter purpose, you'll need to search for frames that have better CPU and memory resources than the source systems. If your goal for using Live Application Mobility is energy management and using it as a server consolidation tool, then resource utilization is not as important.


WPAR manager and Live Application Mobility demo

This section shows how to install WPAR manager and relocate a running WPAR.

First, install the WPAR manager. There are two parts to the process:

  1. Installation of the WPAR manager
  2. Installation of the agent

The agent goes on every system that will be managed by the WPAR manager, while the WPAR manager and centralized database is installed on only one system. Start by installing the filesets for the WPAR manager (see Listing 1).

Listing 1. Installing the filesets for the WPAR manager
# installp -acqgYXd .  wparmgt.mgr
Name                        Level           Part        Event       Result
-------------------------------------------------------------------------------
wparmgt.mgr.rte             1.1.1.0         USR         APPLY       SUCCESS
wparmgt.mgr.rte             1.1.1.0         ROOT        APPLY       SUCCESS
wparmgt.cas.agentmgr        1.3.2.18        USR         APPLY       SUCCESS
wparmgt.cas.agentmgr        1.3.2.18        ROOT        APPLY       SUCCESS
tivoli.tivguid              1.3.0.0         USR         APPLY       SUCCESS
tivoli.tivguid              1.3.0.0         ROOT        APPLY       SUCCESS

# installp -acqgYXd .  wparmgt.db
+-----------------------------------------------------------------------------+
                    Pre-installation Verification...
+-----------------------------------------------------------------------------+
Verifying selections...done
Verifying requisites...done
Results...

SUCCESSES
---------
  Filesets listed in this section passed pre-installation verification
  and will be installed.

  Selected Filesets
  -----------------
  wparmgt.db.db2 1.1.1.0                      # Workload Partitions Manager ...

Installation Summary
--------------------
Name                        Level           Part        Event       Result
-------------------------------------------------------------------------------
wparmgt.db.db2              1.1.1.0         USR         APPLY       SUCCESS
wparmgt.db.db2              1.1.1.0         ROOT        APPLY       SUCCESS

When the filesets are installed, you need to configure the database: # /opt/IBM/WPAR/manager/db/bin/DBInstall.sh -dbinstallerdir /db2 -dbpassword my_password.

When this is completed, you'll need to configure the database connection between the WPAR Manager and the database, and to define the WPAR Agent registration password. While there are three supported modes to run the WPAR manager configurator, we used the console mode -- the non-GUI version -- for our install. We found this to be the simplest method to use.

Listing 2. Console method for running the WPAR manager configurator
lpar55p682e_pub[/tmp/wparmgr] > /opt/IBM/WPAR/manager/bin/WPMConfig.sh -i console
Preparing CONSOLE Mode Installation...
===============================================================================
Choose Locale...
----------------
    1- Catala
    2- Deutsch
  ->3- English
    4- Espanol
    5- Francais
    6- Italiano
    7- Portugues  (Brasil)
===============================================================================
WPAR Manager Configuration Summaryn
----------------------------------
Click Next to configure WPAR Manager with the following values.
Click Cancel to terminate.
WPAR Manager Access:
Public Port: 14080
Secure Port: 14443
Database Access:
Hostname: lpar55p682e_pub
Username: db2wmgt
Password: ********
Service Port: 50000
Name: WPARMGT
Agent Manager, configure local:
Base Port: 9511
Public Port: 9513
Secure Port: 9512
Registration password: ********
  ->1- Next
    2- Cancel
ENTER THE NUMBER OF THE DESIRED CHOICE, OR PRESS <ENTER> TO ACCEPT THE
   DEFAULT:
1
===============================================================================
WPAR Configuration Complete
---------------------------
The configuration of IBM Workload Partitions Manager for AIX has completed
successfully.
PRESS <ENTER> TO EXIT THE INSTALLER: lpar55p682e_pub[/tmp/wparmgr] >

The final piece is installing and configuring the agent, which must be done on each partition that you want managed by the WPAR manager: # installp -acqgYXd <MOUNT_POINT> wparmgt.agent.

When the filesets are installed, this command will configure the agent for you: # /opt/IBM/WPAR/agent/bin/configure-agent -yourhostmachine.

When completed, we're ready to point our browser to the IP address where WPAR manager is configured. I was able to use this from a VNC client after configuring VNServer on the host console or from a standard Firefox browser, even from a PC running Windows®. The latter will work only if you are on the same network as the WPAR manager.

Figure 1. Pointing the browser to the IP address where the WPAR manager is configured
Pointing the browser to the IP address where the WPAR manager is configured

After logging in with your root password, you can validate the managed systems. We had two systems, as illustrated in Figure 2.

Figure 2. Validating the managed systems
validating the managed systems

It is from here, that one adds the WPARs and configures them to be able to be relocatable. You do this by making sure that the filesystems used are NFS and you also check the option that says "checkpointable."

The steps themselves are fairly clear.

  1. Create a working NFS environment on a defined server
  2. Create a WPAR using NFS directories, using the -c option allowing for checkpointable, necessary to use Live Application Mobility
  3. Relocate WPARs.

There are several ways to create WPARs. In Figure 3 we used the WPAR manager.

Figure 3. Create WPARs using WPAR manager
Create WPARs using WPAR manager

In this example (see Listing 3), we'll create a specification file from the command line using mkwpar. There is also a sample file in /usr/samples/wpars -- called sample.spec -- which you can use as a template.

Listing 3. Use mkwpar to create a specification file
# mkwpar -n app20 -h app20 -N interface=en0 netmask=255.255.192.0 
  address=172.29.140.243 -r -c -M directory=/vfs=nfs host=lpar32p682e_pub 
  dev=/scratch/app20root -M directory=/home vfs=nfs host=lpar32p682e_pub 
  dev=/scratch/app20home -M directory=/tmp  vfs=nfs host=lpar32p682e_pub 
  dev=/scratch/app20tmp -M directory=/var  
                  vfs=nfs host=lpar32p682e_pub dev=/scratch/app20var

Now, let's return to the WPAR manager. Regardless of where you create your WPAR, you can relocate your partitions from here as well (see Figure 4).

Figure 4. Start the process of relocating your partitions
Start the process of relocating your partitions

Figure 5 shows that the relocation process is in progress.

Figure 5. The relocation process in progress
The relocation process in progress

It's important to note that even with the GUI, there will be some challenges in terms of getting everything operational, particularly when you first start using the system. We found one interesting bug, when we had used an underscore (_) in the host-name, which kept the WPAR manager from being able to locate one of our managed systems. After removing the underscore we of course got everthing working well, which you've seen in this article.


Summary

In this article, we discussed Live Application Mobility in the context of WPARs and how best to use the system. We defined the differences between Live Application Mobility and Live Partition Mobility. We created WPARs and installed WPAR Manager to help us manage our WPAR environment. Lastly, we created WPARs for the express purpose of using Live Application Mobility and illustrated how to create and move running WPARs from one system to another. It's important to understand that Live Application Mobility does not replace High Availability. While it has several purposes, it is best used when performing scheduling outages, which allows for system maintenance to occur with no downtime. This is a very real and important innovation of AIX 6.1, which neither Solaris nor HP-UX has at this time.

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