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

    Effect: After Parser is as a service, it conforms to Cloud Native idea, can utilize platform advantages, flexible deployment, and horizontal expansion.
    Current Status: With the application deployment, it is not easy to support horizontal expansion, and there is basically no flexibility.

 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

   The first phase： collecting requirements, unifying model input and output, simultaneously implementing model output conversion from object to Json (this is the key point)

   In the second stage： Providing unified restful interface to parser client.

R3 CSAR which exported by SDC in CCVPN use case and CPE use case 

vCPE：

CCVPN: