I have developed Flex – Java – Spring Web Application that I have deployed into an Amazon EC2 image – all is looking great.
However, I need to auto scale and share User requests between multiple instances of the application that sit on different machines, i.e not within the same Tomcat Container. Amazon manages the load balancing and the application uses AMQ topics to communicate critical application level changes between each of the instances.
One of these notifications might be a property. I have several property files that I inject using the @Value annotation into the relevant Spring beans. These property files reside ina properties folder the class path root (classpath:properties/)
When operating on a single node, when I update a property, I update the in memory value using a setter and also write the change back to the relevant property file using FileInputStream and FileOutputStream. This is easy enough.
However, the obvious problem is now what happens when I autoscale and a new instance is started in a different container? This application will read the deployed (old) version of the property file and ultimately behave differently than the other parallel nodes.
I really would like to maintain file based configuration over a Database if I can – I know that the DB solution will be the most prevalent response here, but any suggestions would be appreciated.
Thanks
As far as you are already using JMS topics I’d suggest you to use durable subscription.
If a client needs to receive all the messages published on a topic, including the ones published while the subscriber is inactive, it uses a durable TopicSubscriber. The JMS provider retains a record of this durable subscription and insures that all messages from the topic’s publishers are retained until they are acknowledged by this durable subscriber or they have expired.
Take a look on JMS API: http://docs.oracle.com/javaee/6/api/javax/jms/Session.html#createDurableSubscriber(javax.jms.Topic, java.lang.String)