As described in an earlier post, another concept for cloud computing architectures is the concept of roles. But what exactly is a role? A role is something that shares common functionality. If we talk about a web shop, this web shop might consist of different roles such as:
- Product presentation role
- Shopping cart role
- Order processing workflow role
The initial question of this is: isn’t this called SOA (Service oriented architectures)? The answer is: no. It is very similar to SOA and basically derives a lot of it’s concepts from SOA but it is rather a “SOA of SOA”. A role might contain one or more services, but a service is covered by exactly one role. Let us think about the shopping cart: an architecture for the shopping cart might hold different services. The role itself would be the shopping cart role with services for:
- Shopping Cart modification Service
- Checkout Service
- Payment Service
A role collects different services and makes it easier for us to understand the way how an application is built. With SOA, we can go more into detail and give a better overview for those that have to implement the platform at the end. Different roles should be able to be scaled independently from each other to achieve great elasticity in the cloud. Furthermore, a role should only be in charge of similar tasks. If we think about the shopping cart again, we can definitely say that services in that role are somewhat similar. The illustration below shows how different roles can be built.
With the separation of different roles, it gives us more flexibility to built our platform more reliable. If the platform experiences an outage, less important roles might not receive any compute but the business critical roles will still receive the available resources. Therefore, it is possible to built a matrix on how important each role is and adjust scaling/elasticity to this matrix.
Different Roles are more important for others. In the web shop sample, an important role is the shopping cart since it is the place where the platform generates revenue. Not so important (in the case of an outage) is the comment functionality. If there is a shortage of resources or some serious issues with our platform, the platform can select to disable the comment role and use the now free resources for the shopping cart. However, this approach requires a smart system that can deal with the prioritisation of roles.
Picture Copyright by Moyan Brenn
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