  Function as a Service (FaaS) is a new cloud technology with automated
resource management. Different from traditional cloud computing, each FaaS
cloud function can only run a fixed period of time before being decommissioned.
Furthermore, FaaS cloud providers often update their platforms (e.g., idle
timeout). These changes and their associated impact are not transparent and
could potentially impact the execution of the cloud functions. Hence, in this
paper, we develop a methodology to characterize the cloud function idle timeout
which is the duration a FaaS cloud provider keeps a cloud function instance
alive without serving active traffic. Our study was conducted on three popular
FaaS platforms, namely AWS Lambda, IBM and Azure Cloud Function. Moreover, we
also report how long a cloud function instance can be kept alive when a user
regularly polls the instance. Experimental results show that the idle timeout
period has evolved from 01/2020 till 01/2022.
