  Cloud services are becoming increasingly popular: 60\% of information
technology spending in 2016 was Cloud-based, and the size of the public Cloud
service market will reach \$236B by 2020. To ensure reliable operation of the
Cloud services, one must monitor their health.
  While a number of research challenges in the area of Cloud monitoring have
been solved, problems are remaining. This prompted us to highlight three areas,
which cause problems to practitioners and require further research. These three
areas are as follows: A) defining health states of Cloud systems, B) creating
unified monitoring environments, and C) establishing high availability
strategies.
  In this paper we provide details of these areas and suggest a number of
potential solutions to the challenges. We also show that Cloud monitoring
presents exciting opportunities for novel research and practice.
