Hyperledger Fabric HLF

The Linux Foundation founded the Hyperledger project in Y2015 to advance cross-industry blockchain technologies.
HLF is one of the Framework from "HL Framework & Tools ecosystem" with the primary objective to provide Permissioned with Channel Support. i.e., HLF is one of the blockchain projects within Hyperledger.
Like other blockchain technologies (Etherum), it also has
- a ledger,
- uses smart contracts,
- participants manage their transactions,
- Data Provenance by offering immutable and cryptographically verifiable record of transactions*
Unlike other Blockchain technologies (Ethereum), it differs as
- private and permissioned,
- No open permissionless system,
- No unpermissioned entry to any member/unknown identities to participate in the network,
- No PoW ( “proof of work” protocol to validate transactions and secure the network),
- Membership Service Provider (MSP): Restricted Entry to Members of a Hyperledger Fabric network enroll through a trusted MSP.

Overview of Hyperledger Framework and Tools

Broader ecosystem of HL Framework & Tools:

Key Concpets of Hyperledger FABRIC

Blockchain network

A blockchain network is a technical infrastructure that provides ledger and smart contract (chaincode) services to applications

Block and Chain

A block contains an ordered set of transactions. It is cryptographically linked to the preceding block, and in turn it is linked to be subsequent blocks.

The ledger’s chain is a transaction log structured as hash-linked blocks of transactions. Suuch as, Blockchain B contains blocks 0, 1, 2.

Smart Contract

A smart contract is code (invoked by a client application external to the blockchain network) that manages access and modifications to a set of *key-value pairs* in the *World State* via Transaction.

Chain Code

In Hyperledger Fabric, smart contracts are packaged as chaincode. Chaincode is installed on peers and then defined and used on one or more channels.

World State

*World state* maintains  “current state” of transaction in Ledger, and such data is stored in a state database for efficient reads and queries from chaincode. Supported databases include - *couchDB*.

Channel

A channel is a private blockchain *overlay* which allows for data isolation and confidentiality. A channel-specific ledger is shared across the peers in the channel, and transacting parties must be authenticated to a channel in order to interact with it. Channels are defined by a *Configuration-Block*.

Membership Service Provider

MSP refers to an abstract component of the system that provides credentials to clients, and peers for them to participate in HLF.

Ordering Service

Also known as orderer. A defined collective of nodes that orders transactions into a block and then distributes blocks to connected peers for validation and commit. The ordering service exists independent of the peer processes and orders transactions on a first-come-first-serve basis for all channels on the network.

HLF also leverages Gossip Protocol & Raft Algo for following 3 major functions:

- 1) manages peer discovery and channel membership; 
- 2) disseminates ledger data across all peers on the channel; 
- 3) syncs ledger state across all peers on the channel

The same protocol and Algo is used in Progrium Consul (a distributed computing CONSENSUS Algo for Leader election and worker management), and it is applied in Seneca (a Microservice Framework on Nodejs)

Hyperledger FABRIC, Hyperledger COMPOSER, Hyperledger EXPLORER

Hyperledger FABRIC:

- A very popular Blockchain Network from Hyperledger ecosystem. 
- Whereas other Blockchain Network from Hyperledger ecosystem, such as Hyperledger SAWTOOTH is the 2nd popular network.

Hyperledger EXPLORER:

User-friendly Web application tool from Hyperledger ecosystem to used to 
- view, invoke, deploy or query 
   - blocks,
   - transactions and associated data, 
   - network information (name, status, list of nodes), 
   - chain codes and transaction families, 
   - as well as any other relevant information stored in the ledger.

Reference: Official Link Reference: Video Demo

Hyperledger COMPOSER:

The Hyperledger Composer Playground provides a user interface for the 
- configuration, deployment and testing of a business network. 
- Advanced Playground features permit users to manage 
     - the security of the business network, 
    - invite participants to business networks and 
    - connect to multiple blockchain business networks.