Hi Ka Chun,
Thanks for your question.
For mobile app, I don’t think it is possible to make it as a peer node. There are two possible ways.
(A) mobile app keeps both the signing key and certificate, and acts as a user in an organization in Hyperledger Fabric. In this case, the mobile app needs to handle the installation of user signing key and certificate. Mobile app talks directly to a peer node.
(B) mobile app accesses the API server. The user signing key and cert is kept in API server. The API server then talks to a peer node. In this case the Hyperledger Fabric cannot tell which actual user is sending transactions as they are all “proxied” by API server. And mobile app and API server handles user authentication which is outside the fabric network.
There are tradeoffs between these two ways as you can imagine. I think (B) is more feasible as it has the least impact on the current model, as technically the mobile app doesn’t know the backend is a fabric network. This helps application development, though you need to address the user authentication outside the fabric network.
Hope this helps.
PS: You can reach me on firstname.lastname@example.org for more questions. Stay connected!