Architecture, Development and Training
German only. Heute exklusiv auf deutsch ein Artikel den ich für das DOAG Magazin im Früjahr 2011 geschrieben habe:
Download: Oracle Fusion Middleware und WebLogic Server in der Cloud (PDF)
Teile des Artikels sowie zahlreiche Grafiken sind aus meinem “Middleware and Cloud Computing” entommen. Viel Spaß beim Lesen!
Oracle is eating its own dog food.
Here is an interesting slide set from OOW11 about how Oracle is using it’s own hardware and software.
Still a lot of Oracle appserver to see instead of WebLogic..
For an updated version of this workshop see here or contact me directly.
I’ll be offering a 2-day cloud computing workshop 2+3. May 2011 in city center of Munich. A second event is planned for Sydney later this year and will be announced by the Australian Oracle User Group.
After a basic introduction and the discussion of common misconceptions we will cover advanced topics such as how to achieve true elasticity, load balancing in clouds, queueing, notifications and databases in clouds. This workshop is centered around Amazon Web Services (AWS) technologies such as EC2 EBS images, RDS, SQS, SNS, ELB etc.
The workshop includes a free copy of my Middleware and Cloud Computing book, printed course material, a pre-configured lab environment to take home as a virtual image on DVD.
Please contact me via email for registration and further details.
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Friday morning. Second cup of coffee. I remember the discussion I had yesterday about the differences of RDS read replicas vs. multi-AZ instances in the Amazon compute cloud.
Actually these concepts are completely different. So it is important to pick the right one that supports your design. Here is a short comparison:
| Multi-availability zone instances | Read replicas | |
| Purpose | Availability | Scalability |
| Number of copies | 1 primary + 1 secondary | 1 primary + n secondaries |
| Secondaries used during normal operation? | No | Yes |
| Synchronization | Synchronous | Asynchronous |
| Use with ELB | No (only one active) | Not supported |
| Use with elastic IPs | Not supported | Not supported |
| Cost | Doubles | Per Instance |
And don’t forget you can use a combination of both.
Unfortunately there is a problem with the Apache plugin for WLS10.3.1. It is rather annoying because it spoils the WebLogic cluster experience as such and even worse: it spoils my distributed cluster demo. I reproduced it working with different teams using WLS 10.3.1 / Windows 32 bit / Apache with mod_wl_20 and also mod_wl_22. And typically I encourage all my customers to create a support case concerning this.
Let me explain what happens. Typically the symptoms are the following: In a distributed cluster setup with three managed server m1, m2, and m3 you configure the plugin for load balancing which initially seems to work fine. You can monitor your requests being distributed in a round-robin way, e.g. m2, m3, m1, m2, m3, m1, m2, m3, … Then, if you kill one managed server, let’s say m2, the pattern changes to m1, m3, m1, m1, m1, m1, m1,…. So the load balancing breaks.
There is a bug now mentioned in the release notes of WLS 10.3.2 which is pointing towards the same direction but the description is rather vague.
Last week I could verify the same behaviour on two clusters with WLS 10.3.3 under Windows. I’d recommend you to try it with your Windows installation. It is reproducible even on one machine running three managed servers.
I thought it would be interesting to verify if the error shows up for WebLogic 12c as well – in contrast to the documentation there is currently no proxy plugin with the WebLogic 12c (12.1.1) distribution. So I used the 10.3.5 version for Linux 32 bit and guess what? The behavior is different! It is not perfect (as it used to be in the good old WLS9 days) but Oracle does have a sense of humor apparently. When running 3 managed servers I observe m1,m1,m1,m2,m2,m2,m3,m3,m3,m1,m1,m1,m2… Interesting, hmm? So it load balances but kind of addresses on server n times. Now here is the good surprise: After killing e.g. m2, I see the following pattern: m1,m1,m1,m3,m3,m3,m1,m1,m1,m3… So unlike with the previous 10.x versions there is still load balancing but the plugin keeps assigning a particular server more than once.
UPDATE^2 WebLogic 10.3.5 Apach 2.2 plugin used for WebLogic 12c: I have to correct myself. When trying WLS 10.3.5 plugin for Apache 2.2 on CentOS6 again in 2 different setups, it seems to work fine. I could’t observer the strange lb pattern anymore. So maybe Oracle has some sense of humor but they don’t express it in the way the plugin load balances your request. Better 
Oracle WebLogic Server 12c Book
Oracle Middleware and Cloud Computing Book