A RabbitMQ message bus is leveraged for communication between the vsfwd (RMQ client) and RMQ server process hosted on the NSX manager. The message bus is used by the NSX manager to send various information to the ESXi hosts, including policy rules that need to be programmed on the distributed firewall in the kernel.
NSX Distributed Firewall is a hypervisor kernel-embedded firewall that provides visibility and control for virtualized workloads and networks. You can create access control policies based on VMware vCenter objects like datacenters and clusters, virtual machine names and tags, network constructs such as IP/VLAN/VXLAN addresses, as well as user group identity from Active Directory. Consistent access control policy is now enforced when a virtual machine gets vMotioned across physical hosts without the need to rewrite firewall rules. Since Distributed Firewall is hypervisor-embedded, it delivers close to line rate throughput to enable higher workload consolidation on physical servers. The distributed nature of the firewall provides a scale-out architecture that automatically extends firewall capacity when additional hosts are added to a datacenter.
The NSX Manager web application and NSX components on ESXi hosts communicate with each other through a RabbitMQ broker process that runs on the same virtual machine as the NSX Manager web application. The communication protocol that is used is AMQP (Advanced Message Queueing Protocol) and the channel is secured using SSL. On an ESXi host, the VSFWD (vShield Firewall Daemon) process establishes and maintains the SSL connection to the broker and sends and receives messages on behalf of other components, which talks to it through IPC.