TOSCA ONAP Service Orchestration

The ONAP (Open Network Automation Platform) represents the merger of the Open-O and Open-ECOMP projects with the goal of enabling the creation and management of NFV services. The unified architecture decomposes platform services into several projects, including the Service Orchestrator (SO) which is responsible for the highest level of orchestration to deliver services.

Declarative Or Imperative

Software IS automation by definition. So when considering a high level automation task like orchestration, the natural inclination is to approach it as a traditional software engineering task. Since the early days of operations automation, scripting has been the workhorse. This approach, writing a sequence of instructions tailored to an automation objective, is the imperative approach. The declarative, or model-driven approach to automation does not do away with imperative programming, but rather seeks to make explicit the underlying objective of the programming in the form of a model. By expressing the end goal of the automation as a model, the objective of the automation becomes far more comprehensible than reverse engineering code. Another essential ingredient of the declarative approach is an orchestrator. The orchestrator interprets models, and automates the execution of imperative code sequences based on the model structure. The orchestrator can be focused on a particular model and automation target, for example Openstack HOT/HEAT, or it can be very generic both in terms of model and target automation platform, for example TOSCA/ARIA.