Whose Fault is It? Correctly Attributing Outages in Cloud Services

Abstract

Cloud availability is a major performance parameter in cloud Service Level Agreements (SLA). Its correct evaluation is essential to SLA enforcement and possible litigation issues. Current methods fail to correctly identify the fault location, since they include the network contribution. We propose a procedure to identify the failures actually due to the cloud itself and provide a correct cloud availability measure. The procedure employs tools that are freely available, i.e. traceroute and whois, and arrives at the availability measure by first identifying the boundaries of the cloud. We evaluate our procedure by testing it on three major cloud providers: Google Cloud, Amazon AWS, and Rackspace. The results show that the procedure arrives at a correct identification in 95% of cases. The cloud availability obtained in the test after correct identification lies between 3 and 4 nines for the three platforms under test.