Threat modelling is performed once an application design is created. The goal of threat modelling is to determine any weaknesses in the application and the potential ingress, egress, and actors involved before the weakness is introduced to production. It is the overall attack surface that is amplified by the cloud, and the threat model has to take that into account.

It is false. Platform security is a shared responsibility between cloud service provider and cloud service customer in Platform as a Service(PaaS) model.

According to ENISA (European Network and Information Security Agency) document on Security risk and recommendation, Isolation failure is considered as one of the top risk and is defined as follows Multi- tenancy and shared resources are defining characteristics of cloud computing. This risk category covers the failure of mechanisms separating storage, memory, routing and even reputation between different tenants (e.g, so-called guest-hopping attacks). However it should be considered that attacks on resource isolation mechanisms (e.g. against hypervisors) are still less numerous and much more difficult for an attacker to put in practice compared to attacks on traditional Oss.

All others are characteristics as defined by NIST.