Pivotal Cloud Foundry: 1.10
Pivotal Web Services
Scaling up an app manually in the Pivotal Web Services admin panel kills the old app instances and creates new apps in place of it.
Example: Changing from 2 to 4 instances, stops the 2 existing apps, creates 2 new apps and then starts all 4 instances up.
When you scale the app in the Apps Manager, you can see the following Scale App warming
Are you sure you want to scale <app_name>?
This will cause the app to restart. Hence, the restart is expected behavior when scaling via the Apps Manager.
The reason for the App Manager restarting the app is because the app allows you to change disk space and memory at the same time as scaling the app, and for those operations, the app does need to be restarted to pick up the changes.
If only making changes to the app instance count, use the CF CLI to scale your app without a restart.
cf scale <app_name> -i 4
CF CLI would accomplish the same thing without any downtime.
This is a known issue fixed in Elastic Runtime 1.10.1+, 1.9.18+, and 1.8.40+