We will review and examine various Hyperledger Fabric components and architectures throughout this recipe. Hyperledger Fabric has three core components, which are peers, ordering service, and Fabric CA:
- Peer: A node on the network that maintains the state of the ledger and manages chaincode. Any number of peers may participate in a network. A peer can be an endorser, which executes transactions, or a committer, which verifies the endorsements and validates transactions results. An endorser is always a committer. Peers form a peer-to-peer gossip network. A peer manages the events hub and delivers events to the subscribers.
- Ordering service: Packages transactions into blocks to be delivered to peers, since it communicates only with peers. The ordering service is the genesis of a network. Clients of the ordering service are peers and applications. A group of orderers run a communication service, called an ordering service, to provide an atomic broadcast. The ordering service accepts transactions and delivers blocks. The ordering service processes all configuration transactions to set up network policies (including readers, writers, and admins). The orderer manages a pluggable trust engine (such as CFT or BFT) that performs the ordering of the transactions.
- Fabric CA: Fabric CA is the certificate authority that issues PKI-based certificates to network member organizations and users. Fabric CA supports LDAP for user authentication and HSM for security. Fabric CA issues one root certificate to member organizations and one enrollment certificate to each authorized user.
Hyperledger Fabric also have several important key features and concepts:
- Fabric ledger: Maintained by each peer and consists of two parts: the blockchain and the world state. Transaction read/write and channel configurations sets are written to the blockchain. A separate ledger is maintained for each channel for each peer that joins. The world state has options of either LevelDB or CouchDB, where LevelDB is a simple key-value store and CouchDB is a document store that allows complex queries. The smart contract decides what is written into the world state.
- Channel: Provides privacy between different ledgers and exists in the scope of a channel. Channels can be shared across an entire network of peers, and peers can participate in multiple channels. Channels can be permissioned for a specific set of participants. Chaincode is installed on peers to access the world state. Chaincode is instantiated on specific channels. Channels also support concurrent execution for performance and scalability.
- Organization: Define boundaries within a Fabric blockchain network. Each organization defines an MSP for the identities of administrators, users, peers, and orderers. A network can include many organizations, representing a consortium. Each organization has an individual ID.
- Endorsement policy: The conditions by which a transaction can be endorsed. A transaction can only be considered valid if it has been endorsed according to its policy. Each chaincode is deployed with an endorsement policy. Endorsement system chaincode (ESCC) signs the proposal response on the endorsing peer and validation system chaincode (VSCC) validates the endorsement.
- Membership services provider (MSP): Manages a set of identities within a distributed Fabric network. It provides identities for peers, orderers, client applications, and administrators. Where the identities can be Fabric CA or external CA, MSP provides authentication, validation, signing and issuance. MSP support different crypto standards with a pluggable interface. A network can include multiple MSPs (typically one per organization), which can include TLS crypto material for encrypted communications.
