Magnitude of impact on customization depends on the degree of customization. Some of the very obvious points are reported below.

1. Any dependency on service layer methods of CloudPortal™ Business Manager core code base is not guaranteed to be backward compatible.
2. Many new UI screens are built in CloudPortal Business Manager 2.x and some of the existing ones are changed. This means any customization done for UI requires a careful review.
3. Some of the features, which were not present in CloudPortal Business Manager product earlier and required customization in past to achieve the same, may be supported in product itself now. Refer CloudPortal Business Manager 2.x features for the same.
4. Customization written based on assumption of some columns in database tables may undergo huge impact. Refer to new schema structure for the same.
5. Configuration file to set log levels (log4j.xml) is no longer in use now. New file to configure log levels is located at/usr/share/vts3/config/serviceability.xml. New logging mechanism supports both Log4j and Logback. However, transformation from old configuration file (log4j.xml) to new configuration file (serviceability.xml) is not supported. You have to reconfigure log levels in serviceability.xml.
6. Authorize.Net and CyberSource are the only supported payment gateways. If different payment gateway is used, one needs to write CloudPortal Business Manager connector for the same. For more information, please refer CloudPortal Business Manager Connector Developer guide.
7. All resource strings are persisted in database now. The mechanism to create custom resource strings is described in customization section in the Administration guide.
8. CloudPortal Business Manager now supports multi-level approvals for custom actions (workflows) such as account provisioning, subscription provisioning and account conversions. Any customization done prior should be rewritten using concept of customization bundle, where you can define and customize workflow and activities in structured manner in xml files. CloudPortal Business Manager will process these files and will instrument the customized workflows and activities. For more information refer, creating customized bundle section.
9. If any phase of usage collection and mediation is customized in CloudPortal Business Manager 1.4.x, same needs to be re-implemented using the product features of CloudPortal Business Manager .
10. Impact on CAS: If additional services are added in deployerConfigContext.xml, they need to be re-written after upgrade.
11. Impact on SSL Certificate: After upgrade to CPBM 2.5, re-import the SSL certificate using the command:

    /usr/java/latest/bin/keytool -import -alias alias -keystore /usr/java/latest/lib/security/cacerts --file cert1.cer