Elastic container platforms (like Kubernetes, Docker Swarm, Apache Mesos) fit very well with existing cloud-native application architecture approaches. So it is more than astonishing, that these already existing and open source available elastic platforms are not considered more consequently for multi-cloud approaches. Elastic container platforms provide inherent multi-cloud support that can be easily accessed. We present a solution proposal of a control process which is able to scale (and migrate as a side effect) elastic container platforms across different public and private cloud-service providers. This control loop can be used in an execution phase of self-adaptive auto-scaling MAPE loops (monitoring, analysis, planning, execution). Additionally, we present several lessons learned from our prototype implementation which might be of general interest for researchers and practitioners. For instance, to describe only the intended state of an elastic platform and let a single control process take care to reach this intended state is far less complex than to define plenty of specific and necessary multi-cloud aware workflows to deploy, migrate, terminate, scale up and scale down elastic platforms or applications.