Hyperledger

Question 1

What is Hyperledger

Answer 1

Umbrella project for an open-source software that enables institutions to set up a shared and trustless ledger database for collaboration

Question 2

3 Features of the Hyperledger Fabric

Answer 2

• permissioned network (MSP to enroll new nodes)
• channels and multi-ledger (connections between peers; each member of a channel maintains a copy of the channel’s specific ledger)
• chaincode (network operators (system chaincode) and developers (application chaincode) to define business logic for the whole channel or a transaction)

Question 3

What is the MSP?

Answer 3

Membership Service Provider is responsible for only letting authorised clients join the network.

Question 4

Applications

Answer 4

• handle the UI and enable an end user to use the blockchain

- submit transactions to the network and invoke chaincode calls

Question 5

Ordering Service main task?

Answer 5

Transactions are ordered sequentially

• transactions are put into a block
• blocks are broadcast to peers that hold the chaincode and ledger
• takes care of authentication

Question 6

Ordering Service holds chaincode or ledger?

Answer 6

• consists of one or more ordering nodes. The nodes do not store chaincode or the ledger

Question 7

Ordering Service gets information from?

Answer 7

• applications must submit transactions to an ordering service node.

Question 8

Peer

Answer 8

• comparable to full node in Bitcoin. Maintains the state of the ledger and executes transactions
• delivers events

Question 9

Roles for peers

Answer 9

• committing peer (commits transactions, verifies endorsements, validates transactions)
• endorsing peer (is a committing peer, takes transaction proposals and executes them to create endorsements)

Question 10

What is the chaincode?

Answer 10

• technical container of a group of related smart contracts

- allows to write business logic that changes the state of the ledger

Question 11

Pros of execution-order-validate

Answer 11

• simultaneous TXs & endorsements

Question 12

Limitations of Order-Execute

Answer 12

• sequential execution:
  of transaction sequentially on all peers limits the effective throughput
• non-deterministic code: applications written in general purpose PL need to follow endorsement policies (so be deterministic) otherwise they are rejected by endorsing peers
• confidentiality of execution: (only a few trusted endorsing peers execute the TXs against the chaincode, the rest just updates the state)

Question 13

Transaction flow steps

Answer 13

1. Application submits transaction proposal
2. endorsing peers execute the transaction proposal
3. read/write set is signed and returned to the application
4. signed responses are sent to the ordering service
5. ordering service distributes new block to all committing peers
6. committing peers validate the transaction (RW set is written to the ledger and new block is added)
7. Notify application

Question 14

RAFT

Answer 14

• crash fault tolerant service
• leader is elected among the ordering nodes and that leader replicates messages to the follower nodes
• as long as there is majority of ordering nodes remaining it is crash fault tolerant (CFT)
• step towards byzantine fault tolerance

Question 15

channel

Answer 15

a separate blockchain

• only managed by a subset of all available nodes
• isolates transactions of different ledgers

Question 16

Can a chaincode be deployed on multiple channels?

Answer 16

Yes. A chaincode may be deployed on multiple channels with each instance isolated within its channel

Question 17

Where is the blockchain saved?

Answer 17

on the file system