Background

Multiple TOSCA Parsers have been used in ONAP across different projects.

List some projects as an example::

Here only list part of the projects, not all the parser consumer project.

Now, all projects consume the parser interfaces through the lib library and project chose to use different parser based on the implementation code language

In summary, currently , the same parser function has different implementations, but parser as a common service should be unified and provided as a service not the lib library. 

Advantages of Parser as a Microservice

1. Microservice can be decoupled from applications 

   Effect: The application does not need to know the implementation details of the Passer, only need to pay attention to the results of the analysis.

   Current status: As a Library, an application can use parser only after understanding the internal implementation of Parser.
   
   

2.  Multi-language support

   Effect: Parser provides services through restful, language-independent, and can support any language such as python and java.

   Current Status: There are different Parser tools for different languages, and cross-language support is difficult.

   
   

3. Easy to upgrade 

   Effect: Parser upgrades independently, only keep the external restful interface unchanged. 

   Current Status: The current Parser as Library, the application sees the internal implementation details of Parser, if Lib upgrade, it will affect the application.
   
   

4.  Easy to deploy, support horizontal expansion

    Current Status: With the application deployment, it is not easy to support horizontal expansion, and there is basically no flexibility.

    Effect: After Parser is as a service, it conforms to Cloud Native idea, can utilize platform advantages, flexible deployment, and horizontal expansion.

 Disadvantages of Parser as a microservice

1.  Performance: Compared with the Lib usage, when Parser provides services through restful, the performance will be reduced 

   
   

2. Delay: Compared with the Lib usage, when Parser provides services through restful, the delay will increase

   
   Note： Temporarily there is no data support for  the above performance and delay 

Implementation recommendations

1.  For external interface

    After the tosca parser microservice is implemented, the Lib usage will continue to be provided, and the application can select to use  the microservice or the Library according to the specific requirements scenario

   
   

2.  For Parser implementation

   
   

   1. Requirement Analysis ( which is tracked in SDC Template Type Analysis): collecting requirements, unifying model input and output, simultaneously implementing model output conversion from object to Json (this is the key point)

   2. API Incapsulation: Providing unified restful interface to parser client.

      Option	Description	Advantage	Disadvantage
      1	Parser only provides one naive API with the csar file as input and return complex Object	The parser implementation is relatively simple， just focus on how to build the complex response	Client need to extract the information that they need from complex response locally，will bring more complexity on client side
      2	Parser provides the extension APIs which are more fine-grained and return the specific content in model according to different API invocation	Don’t need to maintain two library code and can solve cross-language issue.	Parser should keep the context information and increase the difficulty of parser implementation

      
      

      
      
      

Supplement

In order to analysis the tosca parser requirements, we do some analysis on the tosca types which currently included and used in SDC and the analysis can be found here: SDC Template Type Analysis

Discussion Minutes (20190102)

• Agreement: SDC Type fix ABC for Dublin
• Target: Parser as a service
• Problem: Rest API definitions for Parser us
• Next Steps:
  • Parser API analysis for run time consumers;
  • Brain Storming in Paris for Parser API design.