## 3 e-Health Cloud Challenges
### Technical Challenges  
* **Availability:** Most healthcare providers require high availability of the e-Health Cloud services. Service and data availability is crucial for healthcare providers who cannot effectively operate unless their applications and patients' data are available. The e-Health Cloud services should be available continuously with no interruptions or performance degradation. Cloud services could experience failures due to software and hardware faults, network faults, security attacks, and natural disasters among many other reasons. As CC resources are distributed over an open network such as the Internet, they will not offer better availability compared to owning and maintaining IT infrastructures within the organization [42]. e-Health Cloud environments need to make serious provisions to react rapidly and efficiently to such outages and ensure service continuity to the participating healthcare providers and other organizations. In addition, hardware and software installations, upgrades, and reconfigurations should be managed such that they are done without any service interruptions for the healthcare providers. * **Data/Service Reliability**: using the cloud for an important application like e-Health Cloud requires assurances of good reliability for the provided services. All e-Health Cloud services and data must be error-free. Some important decisions regarding single human or society health can be taken depending on the data and services provided by the e-Health Cloud. As such services are distributed and may come from a number of Cloud providers, the chance of having faulty or incorrect data or services can increase. The data in e-Health Cloud must be consistent and constantly in a valid state regardless of any software, hardware, or network failures. In addition, all e-Health Cloud must deliver error-free services for healthcare providers. * **Data Management:** Huge numbers of medical records and images related to millions of people will be stored in e-Health Clouds. The data may be replicated for high reliability and better access at different locations and across large geographic distances. Some of the data could be also made available locally. Most medical applications require secure, efficient, reliable, and scalable access to the medial records. These requirements enforce the need to have some storage services that provide fault tolerance, secure storage over public clouds, and rich query languages that allow efficient and scalable facilities to retrieve and process the application data. * **Scalability:** hundreds of healthcare providers with millions of patient records could be handled by an e-Health Cloud, which is only achievable if and only if the services provided are scalable. The ability to scale (grow while maintaining acceptable performance) is one of the most important factors in providing successful cloud services. Cloud scalability is mainly enabled by increasing the capacity and number of IT resources such as compute nodes, network connections, and storage units and providing suitable operational and management facilities. Scalability requires dynamic configuration and reconfiguration as well as an automatic resizing of used virtualized hardware resources [43]. In addition, scalability requires maintaining an acceptable level of performance regardless of the size and utilization levels of the services. * **Flexibility:** an e-Health Cloud must be capable of serving multiple healthcare providers with different requirements. These requirements are in terms of functions, operations, users, auditing, management, and quality of service (QoS) requirements. The e-Health Cloud infrastructures and services should be flexible enough to be configured for different healthcare providers' requirements. In addition, the e-Health Cloud should be very flexible in adding new needed services to support healthcare processes. While e-Health Cloud services must be flexible to meet different healthcare requirements, they also must be easily configurable to meet with different needs.