Consensus in Hyperledger Fabric

Mohan DhawanIBM Research, India

2

Hyperledger Fabric v/s Ethereum

Characteristic Hyperledger Fabric Ethereum

Description of platform Modular blockchain platform Generic blockchain platform

Governance Linux Foundation Ethereum developers

Usage Mission-critical managed enterprise applications

Anonymous “bitcoin-like” network optimized for “volume”, at the expense of managed governance

Mode of operation Permissioned, private Permissionless, public or private

Consensus Broad understanding of consensus that allows multiple approaches

Transaction level

Mining based on Proof of Work (PoW) or Proof of Stake (PoS)

Ledger level

Identity Participants declare who they are and their identities are confirmed

Anonymous

Network “OPEN” by providing transparency of participants

“OPEN” to everyone anonymously

Trust Trust in the parties Transactions can be trusted; parties cannot be trusted as they are anonymous

Smart contracts Smart contract code (e.g., Go, Java, JavaScript)

Smart contract code (e.g., Solidity)

Currency None

Currency and tokens via chaincode

Ether

Tokens via smart contract

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Hyperledger Fabric V1 Architecture

● Ledger is a tamperproof record of transactions replicated across nodes in the network– A blockchain is a decentralized and distributed digital ledger

● Chaincode is a program that typically handles business logic agreed to by members of the network, so it may be considered as a “smart contract”– Initializes and manages ledger state through transactions submitted by

applications

● Types of nodes– Client

● Submits an actual transaction-invocation to the endorsers, and broadcasts transaction-proposals to the ordering service

– Peer● Commits transactions and maintains the state and a copy of the ledger. Besides, peers can

have a special endorser role

– Orderer● Runs the communication service that implements a delivery guarantee, such as atomic or

total order broadcast

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Hyperledger Fabric V1 Architecture

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Ordering Service

ClientApplication

SDK (HFC)

MembershipServicesProvider

Peer

EndorserEndorser

Ledger

CommitterCommitter

AAChaincode BB

!Events

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Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

Application proposes transaction

Endorsement policy:• “E0, E1 and E2 must sign”• (P3, P4 are not part of the policy)

Client application submits a transaction proposal for Smart Contract A. It must target the required peers {E0, E1, E2}

E0E0

E1E1

E2E2

ClientApplication

SDK

Hyperledger Fabric

Ordering-Service

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OOP

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Step 1/7 – Propose Transaction

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Endorsement Policy

● Describes 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 associated with an Endorsement Policy

● Examples of policies– AND('Org1.member', 'Org2.member', 'Org3.member')

– OR('Org1.member', 'Org2.member')

– OR('Org1.member', AND('Org2.member', 'Org3.member'))

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Step 2/7 – Execute Proposal

Endorsers Execute Proposals

E0, E1 & E2 will each execute the proposed transaction. None of these executions will update the ledger

Each execution will capture the set of Read and Written data, called RW sets, which will now flow in the fabric.

Transactions can be signed & encrypted

Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

E0E0

ClientApplication E1E1

E2E2

SDK

Ordering-Service

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OO OO

OOP

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AADD

Hyperledger Fabric

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Step 3/7 – Proposal Response

Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

Application receives responses

RW sets are asynchronously returned to application

The RW sets are signed by each endorser, and also includes each record version number

(This information will be checked much later in the consensus process)

E0E0

ClientApplication E1E1

E2E2

SDK

Ordering-Service

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OO OO

OOP

P4P4P3P3

AABB

AABB

AABB

AADD

Hyperledger Fabric

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Step 4/7 – Order Transaction

Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

Application submits responses for ordering

Application submits responses as a transaction to be ordered.

Ordering happens across the fabric in parallel with transactions submitted by other applications

E0E0

E1E1

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OOP

ClientApplication

SDK

Ordering-Service

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Hyperledger Fabric

(other applications)

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Step 5/7 – Deliver Transaction

Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

Orderer delivers to all committing peers

Ordering service collects transactions into proposed blocks for distribution to committing peers. Peers can deliver to other peers in a hierarchy (not shown)

Different ordering algorithms available:• Solo (Single node, development)• Kafka (Crash fault tolerance)

E0E0

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OOP

ClientApplication

SDK

Ordering-Service

P4P4P3P3

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AADD

Hyperledger Fabric

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Step 6/7 – Validate Transaction

Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

E0E0

E1E1

E2E2 OO

OO OO

OOP

ClientApplication

SDK

Ordering-Service

P4P4P3P3

* * *

*

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AADD

Hyperledger Fabric

Committing peers validate transactions

Every committing peer validates against the endorsement policy. Also check RW sets are valid for world state.

Validated transactions are applied to world state and retained on the ledger.

Invalid transactions are also retained on the ledger but do not update world state.

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Step 7/7 – Notify Transaction

Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

Committing peers notify applications

Applications can register to be notified when transactions succeed or fail, and when blocks are added to the ledger

Applications will be notified by each peer to which they are connected

E0E0

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E1E1

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E2E2

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ClientApplication

SDK

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Hyperledger Fabric

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Ordering Service

● Packages transactions into blocks to be delivered to peers

● Communication with the service is via channels

● Different configurations for the ordering service include– Solo: Single node for development

– Kafka: Crash fault tolerant consensus● 3 nodes minimum, Odd number of nodes recommended

Ordering-Service

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Channels

● Separate channels isolate transactions on different ledgers– Concurrent execution for performance and scalability

● Peers can participate in multiple channels

● Ledgers exist in the scope of a channel – Can be shared across an entire network of peers

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E1E1

E0E0

Ordering-Service

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• All peers connect to the same system channel (blue).

• All peers have the same chaincode and maintain the same ledger

• Endorsement by peers E0, E1, E2 and E3

E0E0

AA

BB

E3E3

E2E2

E1E1

AA

BB

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Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

ClientApplication

SDK

P

Ordering-Service

Hyperledger Fabric

Single Channel Network

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• Peers E0 and E3 connect to the red channel for chaincodes Y and Z

• Peers E1 and E2 connect to the blue channel for chaincodes A and B

E0E0

ZZ

YY

E3E3

E2E2

E1E1

AA

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ClientApplication

SDK

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Ordering-Service

ClientApplication

SDK

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Hyperledger Fabric

Endorser Ledger

Committing Peer Application

Ordering Node

Smart Contract(Chaincode)

Endorsement Policy

Key:

Multi Channel Network

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www.hyperledger.org

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