Sync files across the Managed Server.

Question

We have exploded war deployed in the Weblogic Cluster and in this there is a feature which would create a zip file in the exploded folder and this zip file will be downloaded through the URL. Now the problem in clustered environment is when the application write the zip file which will be available in only one of the managed server and when we try to download the zip file through the LoadBalancer URL it may not hit the same Managed Server in which the zip file is available.
Is there a way in weblogic cluster to sync the files across all the managed server so that we can access the file through loadbalancer.

Answer 1

Hi Suresh
1. Your issue has nothing to do with the cluster setup and the way you deploy the application (as EAR or Exploded). Basically in your application, you generate a file and automatically that gets stored in that machines location. Now when you access it from a load balancer, the request may go to other machine and naturally it will not find the file there. There is nothing in the cluster setup or something that can copy the files and replicate acorss the machines. Infact that will be way too complex. I will couple of solutions.
2. Create a shared folder like public folder. Say in Windows, create a folder with some folder structure and map it as say X: Drive. now this X Drive can be accessed from any other machine like Machine1, Machine2 (after setting the sharing properties). First try directly from Windows Explorer itself. Now within your application, when you generate and store the file, refer this X: Drive with full path. You can make it more flexible by using a .properties file that has key value pair. Key is like FILE_LOCATION and value can be like X:\a\b\c. Now using simple Java Properties class API to load the contents from this file. You can add all the constants, check for if .properties file exist like that. Once you have all the properties loaded, then refer this key, to get its value and use that to store the file generated. Use the same approach, while retrieving the file also. Use the key to get the location and then look for the file you want to download. This should work, when the request goes to any managed server in the cluster. I used it. I created a utility class like MyAppPropertiesLoader, with some static methods, that reads the file only once, if it is null, and then get values using simle methods like getString(String aKey), getLong(String aKey) etc. The huge BENEFIT of this is, once you deploy the application say in Unix, natually, the shared location has to be one of the unix boxes. Then just mount this location on both the managed servers (mount is similar to mapping a drive in Windows OS). Also the location of the files can be changed anytime in the properties file. Say in QC, the location may be X:\a\b\c\qc. But for UAT on Unix it can be like /x/y/z/uat/. Now this .properties file can exist directly under the Domain root folder so you can access it directly without any path in your java code. You can also use System properties like user.home etc. Make sure to copy this .properties file on both the domains. The original master domain. And the psueduo domain that is generated when you run the unpack command if you have managed server in another machine.
3. This is much simpler but kind of not recommended. Simply, create a simple table with few header columns and one BLOB/CLOB column. Store the file in this database table and retrieve from it. This means you will have JDBC code, and the code to create clob to store and generate file from clob for retrieval.
My preference is the first option given above. Getting tools to copy files may be complex. Its not like syncing the data across but its the files that needs to be copied across the machines.
Thanks
Ravi Jegga