Deployments can get stuck when scaled to 0 #4250
Description
Reproduce Steps
- Push an application with 1 instance
- Push again with rolling deployment with 0 instances
cf push "static" -b staticfile_buildpack -i 0 --strategy=rolling - Observe that the deployment is stuck in
DEPLOYING - Observe in the logs
{"timestamp":"2025-03-10T22:31:58.615385458Z","message":"error-scaling-deployment","log_level":"error","source":"cc.deployment_updater.update","data":{"deployment_guid":"12ec3f1d-4b80-4098-8855-ddd93d010124","error":"NoMethodError","error_message":"undefined method `lock!' for nil:NilClass","backtrace":"/var/vcap/data/packages/cloud_controller_ng/708214c425d84329afca8ddad9f998cf8219d3e4/cloud_controller_ng/lib/cloud_controller/deployment_updater/actions/scale.rb:31:
This seems like its related to https://github.com/cloudfoundry/cloud_controller_ng/blob/main/lib/cloud_controller/deployment_updater/actions/scale.rb#L57 when there are no process instances > 0 this returns nil. Presumably min_by returns null if given an empty array