  Most softwarized telco services are conveniently framed as Service Function
Chains (SFCs). Indeed, being structured as a combination of interconnected
nodes, service chains may suffer from the single point of failure problem,
meaning that an individual node malfunctioning could compromise the whole chain
operation. To guarantee "highly available" (HA) levels, service providers are
required to introduce redundancy strategies to achieve specific availability
demands, where cost constraints have to be taken into account as well. Along
these lines we propose HASFC (standing for High Availability SFC), a framework
designed to support, through a dedicated REST interface, the MANO
infrastructure in deploying SFCs with an optimal availability-cost trade off.
Our framework is equipped with: i) an availability model builder aimed to
construct probabilistic models of the SFC nodes in terms of failure and repair
actions; ii) a chaining and selection module to compose the possible redundant
SFCs, and extract the best candidates thereof. Beyond providing architectural
details, we demonstrate the functionalities of HASFC through a use case which
considers the IP Multimedia Subsystem, an SFC-like structure adopted to manage
multimedia contents within 4G and 5G networks.
