3.1.2 Resource selection and preferences

Cloud Fog Service Broker (CFSB) is designed to facilitate the evaluation and selection of the resources within the cloud continuum ecosystem. The CFSB employs Multiple-Criteria Decision Making (MCDM)  methods that rely on Mathematical Programming to assess resources based on multiple factors. This integration allows for a comprehensive assessment, ranking resources by synthesizing these diverse criteria and incorporating user preferences through weight restrictions in optimization models.

CFSB provides a GUI for the application owner to select the criteria an express his/her preferences over them. This information is stored to be used later when communicating with the Optimizer component and evaluating the available resources.  For the application owner the CFSB cab accessed from  https://cfsb.cd.nebulouscloud.eu/ .

We illustrate the Cloud Fog Service Broker component by evaluating 10 available resources using 3 criteria.

Selection of 3 criteria, i.e., Memory Size, Number of Cores and Reputation, from the available list of criteria.

The criteria values of the resources are exhibited in Fig. 2. As it can be seen, three criteria were chosen, namely Memory Size, Number of CPU Cores and Reputation. The criterion Reputation is ordinal and receives values using a three point Likert scale {Low, Medium, High}.

Τhe following figure exhibits the graphical interface where the user can express his preferences over the criteria, which are translated into relative and immediate constraints. For instance, the use believes that the criterion Memory Size is two times more important than the criterion Reputation. Also, the user imposes the immediate constraint on the weight that corresponds to criterion Reputation to receive a value higher than 0.1 from the optimization process.

The scores and ranking for the 10 available resources under evaluation are presented below. As we can see, only one resource is ranked at the first level. Namely, an edge device from 7Bulls located in Warsaw, with Debian operating system, 2 cores and 2048 MB RAM. Although there are available resources with better specifications, the result depicts the less the better policy assumed for this application.

The data and results of the evaluated nodes are saved in order to be used whenever Optimizer component asks CFSB to evaluate the available resources for this specific application.