Java web application short lived caching

Question

I need to develop a Spring web application that needs to query a legacy system based on certain criteria (location). In order to reduce the load on the legacy system we wanted to extract data every 30 seconds for all locations in a single query and keep in-memory to serve client requests. Clients gets refreshed periodically (every minute). Web application does not write anything to the database.

The application is deployed to a tomcat cluster with at least two nodes.

In the above scenario what is the best way to implement in-memory data-store? We want to execute the query in only one tomcat node (say primary) and synchronize data to the other node (say secondary). When the primary node goes down, the secondary node should start executing the query to serve clients.

Answer 1

In the above scenario what is the best way to implement in-memory data-store?

You could use any distributed cache, such as, EHCACHE or Terracotta. With the right configuration, the cached data will be replicated to all the servers in the Tomcat cluster.

We want to execute the query in only one tomcat node.

Since you are using a Tomcat cluster, the clustered servers are most likely already behind a load balancer of some sort and your application is likely accessed as http://www.domain.com. This means, every request to a URL on www.domain.com is being routed to one of the clustered servers automatically by the load balancer.

A simple strategy would be to refresh the cache using an HTTP call, such as, curl http://www.domain.com/cache/refresh. Since this call will go through the load balancer, it will be automatically routed to one of the servers in the Tomcat cluster whenever invoked.

Now, just configure a cronjob to hit the cache refresh URL at your desired frequency. The cronjob can be configured on one of your servers, or use one of the many available web-based cron services.