  Nowadays, most telecommunication services adhere to the Service Function
Chain (SFC) paradigm, where network functions are implemented via software. In
particular, container virtualization is becoming a popular approach to deploy
network functions and to enable resource slicing among several tenants. The
resulting infrastructure is a complex system composed by a huge amount of
containers implementing different SFC functionalities, along with different
tenants sharing the same chain. The complexity of such a scenario lead us to
evaluate two critical metrics: the steady-state availability (the probability
that a system is functioning in long runs) and the latency (the time between a
service request and the pertinent response). Consequently, we propose a
latency-driven availability assessment for multi-tenant service chains
implemented via Containerized Network Functions (CNFs). We adopt a multi-state
system to model single CNFs and the queueing formalism to characterize the
service latency. To efficiently compute the availability, we develop a modified
version of the Multidimensional Universal Generating Function (MUGF) technique.
Finally, we solve an optimization problem to minimize the SFC cost under an
availability constraint. As a relevant example of SFC, we consider a
containerized version of IP Multimedia Subsystem, whose parameters have been
estimated through fault injection techniques and load tests.
