Definition: The Composer REST Server is a component of the Hyperledger Composer framework that enables the deployment of a RESTful API based on a business network defined in Hyperledger Composer. This RESTful API allows applications to interact with the blockchain business network using standard HTTP methods.

Key Features:

• Auto-generation of APIs: It automatically generates a RESTful API based on the business network’s model definition, which can reduce the time and effort required to integrate applications with a blockchain network.
• Secure Access: Integrates with identity and access management tools, ensuring secure access to the blockchain data.
• Flexible Deployment: Can be run as a standalone server or can be embedded in existing Node.js applications.
• Multi-user Mode: Enables authentication and identification of individual users, mapping them to identities on the blockchain.

Components:

• LoopBack: The Composer REST Server is built on top of the LoopBack framework, which is a highly extensible open-source Node.js framework that allows for the quick creation of APIs.
• Swagger UI: Provides a user interface that allows users to explore and test the generated RESTful API.

Usage:

• Integration with External Systems: The auto-generated RESTful API allows for seamless integration with external systems, web applications, or mobile apps.
• Rapid Prototyping: Developers can quickly prototype and test business network interactions using the provided Swagger UI.
• Data Queries: Facilitates querying of data on the blockchain network through HTTP requests.

Considerations:

• Performance: As a middle layer, the Composer REST Server may introduce latency when processing a large number of requests. Optimizing the server and its configuration can help mitigate this.
• Deprecation: It’s important to note that as of late 2019, the Hyperledger Composer project was deprecated by the Linux Foundation’s Hyperledger project. While the tools still exist and can be used, they are no longer actively maintained or updated.

Alternatives: With the deprecation of Hyperledger Composer, other solutions like Hyperledger Fabric’s native SDKs for Node.js, Java, and Go have become more popular for creating applications that interact with Hyperledger Fabric networks.

In summary, the Composer REST Server was a tool in the Hyperledger Composer toolkit that facilitated the creation of RESTful APIs for blockchain business networks. It automated much of the process, making it easier for developers to focus on business logic rather than integration details. However, with the deprecation of Hyperledger Composer, other methods have become prevalent for building blockchain applications.