How to Use Automatic Failover In an ActiveMQ Network of Brokers

Update: Here is the tarball of ActiveMQ configurations used for this blog post.

Last week I tested a new feature in ActiveMQ 5.3.0 to support automatic failover/reconnect in a network of brokers. Besides adding this information to the ActiveMQ book, one person also suggested that I also post it on my blog for easier access, so here you go!

Folks familiar with ActiveMQ already know that a network of brokers allows many broker instances to be networked for massive scalability. Prior to the addition of this feature in ActiveMQ 5.3, if one of the brokers in the network went down, reestablishing a connection with that broker when it comes back up is a manual process wrought with difficulty. By adding support for failover to the network of brokers, any broker in the network can come and go at will without any manual intervention. A very powerful feature, indeed. Although this post is long, the outcome of the testing is well worth it.



The first thing to note is the topology for the network of brokers. I used a network of three brokers named amq1, amq2 and amq3. The attached diagram explains the topology, including the consumers and producers. amq1 and amq2 are stand alone with no network connector. amq3 defines a network connector with failover to amq1 and amq2. Consumers exist on amq1 and amq2. Producer will connect to amq3. To start with, I have only configured a uni-directional network connector in amq3. Later I will change the configuration for a bi-directional network connector.

Thanks to the ability to upload any file to Google Docs this week, you can download the configuration files for the three brokers.

The next thing to do is outline the steps I used to test out this feature. These steps were performed on Mac OS X (Unix) but could easily be adapted for Windoze. Below are those steps:

1) Open six terminal windows as defined below:
1a) Terminal 1 = cd into the amq1 dir
1b) Terminal 2 = cd into the amq2 dir
1c) Terminal 3 = cd into the amq3 dir
1d) Terminal 4 = cd into the amq1/example dir
1e) Terminal 5 = cd into the amq1/example dir
1f) Terminal 6 = cd into the amq1/example dir

2) Terminal 1: start up amq1 (./bin/activemq)
3) Terminal 2: start up amq2 (./bin/activemq)
4) Terminal 3: start up amq3 (./bin/activemq)

Thanks to the configuration of the ActiveMQ logging interceptor, you should see that amq3 makes a network connection to either amq1 or amq2. For the rest of these steps, let's assume that amq3 connected to amq1.

5) Terminal 4: start up a consumer on amq1 (ant consumer -Durl=tcp://0.0.0.0:61616)
6) Terminal 5: start up a consumer on amq2 (ant consumer -Durl=tcp://0.0.0.0:61617)
7) Terminal 6: start up a producer on amq3 (ant producer -Durl=tcp://0.0.0.0:61618)

You should see 2000 messages sent to amq3. The messages should be forwarded to either amq1. The consumer connected to amq1 should have received the 2000 messages and shut down.

8) Terminal 1: shut down amq1 (ctrl-c)

Note the logging that shows the failover taking place successfully. Let's test it to see if the demand forwarding bridge actually got started.

9) Terminal 6: start up a producer on amq3 (ant producer -Durl=tcp://0.0.0.0:61618)

You should see 2000 messages sent to amq3. The consumer connected to amq2 receives the 2000 messages and shuts down.

10) Terminal 1: start up amq1 (./bin/activemq)

11) Terminal 2: shut down amq2 (ctrl-c)

Again, the failover took place successfully. Let's continue just a bit further to see if it will continue to failover if I bring up amq1 again.

12) Terminal 4: start up a consumer on amq1 (ant consumer -Durl=tcp://0.0.0.0:61616)

13) Terminal 6: start up a producer on amq3 (ant producer -Durl=tcp://0.0.0.0:61618)

You should see 2000 messages sent to amq3. The consumer connected to amq1 receives the 2000 messages and shuts down.

This proves that the failover transport is supported in a network connector and it does work correctly with a uni-directional network connector. In addition to a uni-directional network connector, I also tested a bi-directional network connector. This only requires a slight change to the configuration of the network connector in amq3. In the amq3 XML configuration file, in the network connector element, add a duplex=true attribute. Below is the network connector element for amq3 with the change:

<networkConnector name="amq3-nc" 
  uri="static:(failover:(tcp://0.0.0.0:61616,tcp://0.0.0.0:61617))" 
  dynamicOnly="true" 
  networkTTL="3" 
  duplex="true" />

With this minor change in configuration, the network connector is now bi-directional. I.e., communication between amq3 and whichever broker it connects to is two-way instead of just one-way. This means that messages can be sent in either direction, not just in one direction originating from amq3.

Below are the steps I used to test this specific change:

1) Open five terminal windows as defined below:
1a) Terminal 1 = cd into the amq1 dir
1b) Terminal 2 = cd into the amq2 dir
1c) Terminal 3 = cd into the amq3 dir
1d) Terminal 4 = cd into the amq1/example dir
1e) Terminal 5 = cd into the amq1/example dir

2) Terminal 1: start up amq1 (./bin/activemq)
3) Terminal 2: start up amq2 (./bin/activemq)
4) Terminal 3: start up amq3 (./bin/activemq)

You should see that amq3 makes a network connection to either amq1 or amq2. For the rest of these steps, let's assume that amq3 connected to amq1.

5) Terminal 4: start up a consumer on amq1 (ant consumer -Durl=tcp://0.0.0.0:61616)
6) Terminal 5: start up a producer on amq3 (ant producer -Durl=tcp://0.0.0.0:61618)

You should see 2000 messages sent to amq3. The messages should be forwarded to amq1. The consumer connected to amq1 should receive the 2000 messages and shut down.

Let's test the duplex capability of the network connector in amq3 now. To do this we'll send messages to amq1 and consume those messages from amq3.

7) Terminal 4: start up a consumer on amq3 (ant consumer -Durl=tcp://0.0.0.0:61618)
8) Terminal 5: start up a producer on amq1 (ant producer -Durl=tcp://0.0.0.0:61616)

You should see 2000 messages sent to amq1. The messages should be forwarded to amq3. The consumer connected to amq3 should receive the 2000 messages and shut down. This proves that the duplex feature is working. Now let's cause a failover/reconnect to take place and run through this same set of steps with amq3 and amq2.

9) Terminal 1: shut down amq1 (ctrl-c)

Notice the logging that shows the failover taking place successfully so that amq3 connects to amq2 now.

10) Terminal 4: start up a consumer on amq2 (ant consumer -Durl=tcp://0.0.0.0:61617)
11) Terminal 5: start up a producer on amq3 (ant producer -Durl=tcp://0.0.0.0:61618)

You should see 2000 messages sent to amq3. The messages should be forwarded to amq2. The consumer connected to amq2 should receive the 2000 messages and shut down.

Now let's test the duplex feature in the network connector.

12) Terminal 4: start up a producer on amq2 (ant consumer -Durl=tcp://0.0.0.0:61617)
13) Terminal 5: start up a consumer on amq3 (ant producer -Durl=tcp://0.0.0.0:61618)

You should see 2000 messages sent to amq2. The messages should be forwarded to amq3. The consumer connected to amq3 should receive the 2000 messages and shut down.

This proves that the duplex feature of the network connector works after a failover/reconnect to amq2.

This is a great addition to ActiveMQ that really improves the usability of a network of brokers. I already have some very large clients using this feature successfully, some of which are using a network of over 2000 brokers.

Hopefully these steps are clear enough to follow for your own use. If you need any clarifications, please contact me.

Update: Here is the tarball of ActiveMQ configurations used for this blog post.

Grrr - What Happened to Java 1.5 on Snow Leopard?!

Just this week I updated to Mac OS X Snow Leopard (10.6.2) only to discover that it removes Java 1.5 entirely - WTF?! I have no idea why Java 1.5 was removed but it was a bad decision. How is it logical that Java 1.3 is reinstalled but Java 1.5 is removed? Anyway, after some searching and a bit of trial and error on my system, here are steps that I had to take to fix this situation:

1. Download Java for Mac OS X 10.5 Update 4


2. IMPORTANT!!! Make sure to run the following two commands BEFORE proceeding:
   
   
   
   1. sudo rm /System/Library/Frameworks/JavaVM.framework/Versions/1.5
   
   
   2. sudo rm /System/Library/Frameworks/JavaVM.framework/Versions/1.5.0
   
   
   
   This removes the old Java 1.5 sym links to prevent the Java 1.6 directory from being overwritten (very bad)


3. Using the Finder, locate the JavaForMacOSX10.5Update4.dmg file and double-click on it to mount the disk image


4. Create a sym link to a missing utility:
   
   
   
   1. sudo ln -s /usr/bin/update_dyld_shared_cache /usr/bin/update_prebinding
   
   
   
   This command fixes a missing sym link in Snow Leopard that is needed by the Pacifist in the next step


5. Using the Pacifist, open the JavaForMacOSX10.5Update4.pkg file from the mounted disk image

In the Pacifist, navigate to /System/Library/Frameworks/JavaVM.framework/Versions and follow these steps:



1. Right-click on 1.5 and select 'Install to Default Location'


2. Right-click on 1.5.0 and select 'Install to Default Location'

After going through these steps, Java 1.5 should now be installed on the system. You can see this by listing the following:

$ ls -l /System/Library/Frameworks/JavaVM.framework/Versions/1.5
lrwxr-xr-x  1 bsnyder  staff  5 Nov 12 13:47 /System/Library/Frameworks/JavaVM.framework/Versions/1.5 -> 1.5.0
$ ls -1 /System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/
Classes
Commands
Headers
Home
Libraries
Resources

NOTE: Through my travels, I've found that many people have no idea that you could switch between different versions of Java. To make the task of switching extremely easy, grab my friend David's setjdk script and use it to handle this task from the command line. It's a bash script that even supports tab completion. So once the script is set up in your environment, switching between versions of Java is as easy as running the following command to see the available Java versions:

$ setjdk <tab>

Then just choose the version you'd like to use, e.g.:

$ setjdk 1.5
Setting this terminal's JDK to 1.5 ... java version "1.5.0_19"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_19-b02-304)
Java HotSpot(TM) Client VM (build 1.5.0_19-137, mixed mode, sharing)


UPDATE: I had to use the steps above to reinstall the documentation for Java 1.5 as well. I found it in the Java for Mac OS X 10.5 Update 4 Developer Documentation. This placed the appledocs.jar, the doc.jar and the src.jar files into the /System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/Home directory. Then I just expanded the doc.jar file to be able to browse the API docs for Java 1.5 via a browser.

SpringSource University in Denver

On Tuesday morning I had just returned from a run at about 9:35am and was checking my messages before I showered and began working for the day. As I was reading various messages, dripping sweat and sipping on some water, I was pinged by my friend and colleague Filip Hanik on IRC. He told me that he was sitting in a classroom in Denver for the SpringSource University Core Spring Training. Here's how the conversation went:

Filip: hey
Bruce: hey, what's up?
Filip: sitting at Core Spring in Denver, but there is no trainer
Bruce: whoops
Bruce: sorry to hear that, is there anything I can do to help?
Filip: yeah, you can come down here and teach this course :)
Bruce: are you serious?
Filip: yes
Bruce: headed for the shower now, see you about 11

By 11am I was in Denver and teaching the first day of the course.

Lucky for me, Chris Beams, a stellar consultant/engineer/trainer at SpringSource, was en route to deliver the rest of the course. Chris arrived later Tuesday evening and taught the course for the rest of the week through Friday and I was lucky enough to sit in. Chris went the extra mile to arrive early and stay late for the rest of the week and even wound up finishing on time on Friday afternoon, a testament to his talents, for sure.

Using Maven? You Should Be Using m2eclipse

If you use Maven for your Java projects, then you should take a look at m2eclipse plugin for Eclipse. After all, there's now a whole book on m2eclipse instead of just a single chapter!

Enterprise Integration Patterns in Practice at JavaOne 2009

Last week I was in San Francisco to speak at JavaOne 2009 to deliver a talk named Enterprise Integration Patterns in Practice where I co-presented with Andreas Egloff from Sun.

We talked about implementing EIP patterns using Apache Camel and Sun's Fuji. I used ActiveMQ in my demo which was rather short but worked well (yay! the demo gods smiled on me last week :-) ) and Andreas showed off Sun's web-based EIP editor. Although this editor looks very cool and Andreas showed how to edit scripting code in each component on the diagram, it left me wondering how it interfaces with Java code. After our demos, my laptop would not flip back to the presentation at the end (which presented an abrupt ending) but still we received a lot of complements throughout the rest of the week.

Beyond the talk, I got to see tons of friends who I don't see that often throughout the year including Debbie, Guillaume, Hiram and Rob, as well as many new SpringSource colleagues (since the acquisition of Hyperic). I also met many, many new folks including Colin and Jamie. I was also lucky enough to eat Thai food twice (love the yellow curry) and sushi once during the week - mmmmmmmmmmm.

If you would like a copy of the presentation, just drop me an email and I'll send it your way (bruce DOT snyder AT gmail DOT com). I'm not sure how much sense the slides will make without the delivery, but it seems like folks are always requesting my presentations after the fact.

JeOS, Oracle XE and VMware on MacOS X

Last week I installed Ubuntu JeOS (Just Enough Operating System) on VMWare Fusion. JeOS is a slimmed-down version of Ubuntu specifically made for installation in a virtual machine so that it has a much smaller footprint than the normal Ubuntu distribution. Anyway, I did this so that I'd have a VM with a smaller footprint that I can use on my MacBook Pro for development and testing.

After setting up JeOS, I installed Oracle XE, a slimmed down version of Oracle that is free for development and distribution. I used these instructions for installing Oracle XE on Ubuntu but there were some catches, namely that by default the web application for Oracle XE was bound to the localhost, i.e., I couldn't see the web app from Firefox in MacOS X. This was easily remedied via this comment on a blog post about this very topic:

Set up the environment on JeOS to use sqlplus:

export ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server
export PATH=${PATH}:${ORACLE_HOME}/bin

Now use the Oracle sqlplus command-line utility to alter a setting that disables local-only access to Apex. Below is the command to run:


$ sqlplus system@xe
Enter password: SYSTEM_password

SQL> EXEC DBMS_XDB.SETLISTENERLOCALACCESS(FALSE);


Now that I could access the Apex webapp (http://127.0.0.1:8080/apex) that is installed with Oracle XE and I was able to use Apex create a user for myself. After this, I could access Oracle XE from MacOS X.

This setup has been working very well for me until today. For no apparent reason, the networking in JeOS went flaky and I could not access the outside world at all. I switched between NAT and host-only networking in VMWare multiple times, rebooting the VM each time - no dice. I upgraded to the latest VMWare Fusion - no dice. I could SSH into the VM from MacOS but that was it. No commands from JeOS would reach the outside world. So on a whim, I reran the vmware-install.pl script again and after that the networking seems to work again. I still have no idea why this happened which is a bit troubling. I don't want to just blindly keep running the install script again with no idea why it's fixing this networking issue.

Update

I guess the networking issue is common enough that Fusion provides a script to restart everything underneath of Fusion, e.g.:

/Library/Application\ Support/VMware\ Fusion/boot.sh --restart

Also, there's a good document available for Understanding Networking in VMware Fusion if you're interested. It's brief and to the point.

SpringSource Tool Suite Now Available For FREE!

Last week in Amsterdam, at the SpringOne EU conference, it was announced that the SpringSource Tool Suite (STS) is now available for FREE! I was very pleased that we made this move as STS is an excellent set of Eclipse-based development tools that can make your Java development much more productive.

If you use Eclipse for your Java development and you use the Spring Framework, then you should really take STS for a spin. It's just like using the Eclipse you know and love but with many added features to make your development more productive. Download the SpringSource Tool Suite now!

I also saw many great talks at SpringOne EU that showcased STS via demos using it. Here is a partial list of some that I saw:

• Development using the Spring Framework; editing Spring XML files is so much easier with STS.


• Demos of OSGi development using the SpringSource dm Server


• Many demos using the feverishly popular (and close to me because I work on it) SpringSource tc Server (BTW, the interest in tc Server is through the roof! Who knew it would be such a hit?)


• Numerous Grails demos using SpringSource tc Server


• Combined with the official unveiling of SpringSource Roo, the increase in productivity surprised even me.

One of the demos that stands out in my mind was delivered by Adrian Colyer during his keynote on day two that utilized many technologies. But the thing I remember the most (and wish that I had more time to play with) was the use of the AWS Toolkit for Eclipse and Chris Richardson's Cloud Foundry, both for working with app deployment and monitoring in the cloud. The ease with which Adrian deployed apps to Amazon EC2 and was able to monitor them were amazing. I say it was amazing because I started working with Amazon EC2 from the command line before any such polished tools were available. It is really great to see the ever-increasing ease of working with cloud-based platforms. If you haven't checked out these two tools and you work with Amazon EC2, I highly encourage you to take some time to do so. Coupled with STS, they will make your life much, much easier.

I have to say it is very cool to see the products all come together like this. It's also awesome to watch demos delivered by folks who know each tool so well. It makes me wish that we had more face-to-face meetings so that I could sponge more of the product knowledge from folks!