Create README.md

Author: abh1kg

product-service/README.md

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+## Product Backend Microservice
+
+This directory represents a sample backend service on the Cloud Foundry platform. Incidentally, the service here implements a product catalog 
+and exposes OAuth-protected REST APIs that allow authorized users to add and view products for their individual consumer accounts. The service 
+is inherently multi-tenant aware.
+
+### Technologies & Libraries used
+
+- The backend service is implemented using NodeJS and uses the node.js buildpack to run on Cloud Foundry
+- The backend service application uses the popular NodeJS web application framework [ExpressJS](https://expressjs.com/en/4x/api.html)
+- The backend service uses a service instance of XS UAA on Cloud Foundry for setting up the OAuth authorizations and role checks at runtime.
+It uses a utility [SAP-provided NPM library](https://help.sap.com/viewer/4505d0bdaf4948449b7f7379d24d0f0d/2.0.03/en-US/54513272339246049bf438a03a8095e4.html) 
+called [node-xssec](https://help.sap.com/viewer/4505d0bdaf4948449b7f7379d24d0f0d/2.0.03/en-US/54513272339246049bf438a03a8095e4.html#loio54513272339246049bf438a03a8095e4__section_atx_2vt_vt)
+for JWT token validations, OAuth scope and privilege checks and setting the security context per authorized HTTP request
+- The service maintains a [database connection pool](https://en.wikipedia.org/wiki/Connection_pool) per consumer subaccount (i.e. consumer's associated PostgreSQL instance). The
+connection pools are initialized on startup of the application runtime or lazily loaded on the first HTTP request.
+  - It is recommended to use an asynchronous messaging system like [RabbitMQ](https://cloudplatform.sap.com/capabilities/product-info.RabbitMQ-on-SAP-Cloud-Platform.b011738d-fa31-4dc4-98b5-cb9acd9aea97.html) 
+  to publish an event that represents a new subscription which can be subscribed to by all application instances that need to be aware of new connections
+  - _Note_ that each PostgreSQL instance has a limit on the maximum number of active connections- the connection pool size for each database service instance per application 
+  instance must be cautiously and intelligently handled so that there is no chance of overcommitting on resources. Overcommitting on connection resources in the pool 
+  can lead to blocked TCP connections at runtime if not handled properly in code