Automating the Upgrade of IaaS Cloud Systems

The different resources providing an Infrastructure as a Service (IaaS) cloud service may need to be upgraded several times throughout their life-cycle for different reasons, for instance to fix discovered bugs, to add new features, or to fix a security threat. An IaaS cloud provider is committed to each tenant by a service level agreement (SLA) which indicates the terms of commitment, e.g. the level of availability, that have to be respected even during upgrades. However, the service delivered by the IaaS cloud provider may be affected during the up-grade. Subsequently, this may violate the SLA, which in turn will impact other services rely-ing on the IaaS. Our goal in this thesis is to devise an approach and a framework for automat-ing the upgrade of IaaS cloud systems with minimal impact on the services and with respect to the SLAs. The upgrade of IaaS cloud systems under availability constraints inherits all the challenges of the upgrade of traditional clustered systems and faces other cloud specific challenges. Similar challenges as in clustered systems include the potential dependencies between resources, po-tential incompatibilities along dependencies during the upgrade, potential system configura-tion inconsistencies due to the upgrade failures and the minimization of the amount of used resources to complete the upgrade. Dependencies of the application layer on the IaaS layer is an added challenge that must be handled properly. In addition, the dynamic nature of the cloud environment poses a new challenge. A cloud system evolves, even during the upgrade, according to the workload changes by scaling in/out. This mechanism (referred to as autoscal-ing) may interfere with the upgrade process in different ways. In this thesis, we define an upgrade management framework for the upgrade of IaaS cloud systems under SLA constraints. This framework addresses all the aforementioned challenges in an integrated manner. The proposed framework automatically upgrades an IaaS cloud sys-tem from a current configuration to a desired one, according to the upgrade requests specified by the administrator. It consists of two distinct components, one to coordinate the upgrade, and the other one to execute the necessary upgrade actions on the infrastructure resources. For the coordination of the upgrade process, we propose a new approach to automatically identify and schedule the appropriate upgrade methods and actions for implementing the up-grade requests in an iterative manner taking into account the vendors’ descriptions of the in-frastructure components, the SLAs with the tenants, and the status of the system. This ap-proach is also capable of handling new upgrade requests even during ongoing upgrades, which makes it suitable for continuous delivery. In case of failures, the proposed approach automatically issues localized retry and undo recovery operations as appropriate for the failed upgrade actions to preserve the consistency of the system configuration. In this thesis, to demonstrate the feasibility of the proposed upgrade management framework we present a proof of concept (PoC) for the upgrade IaaS compute, and its application in an OpenStack cluster. In this PoC, we target the new challenge of upgrade of the IaaS cloud (i.e. unexpected interference between the autoscaling and the upgrade processes) compared to the clustered systems. In addition, the prototype of the proposed upgrade approach for coordinat-ing the upgrade of all kinds of IaaS resources has been implemented and discussed in this thesis. We also provide an informal validation and a rigorous analysis of the main properties of our approach. In addition, we conduct experiments to evaluate our approach with respect to SLA constraints of availability and elasticity. The results show that our approach avoids the outage at the application level and reduces SLA violations during the upgrade, compared to the traditional upgrade method used by cloud providers