In Hyperledger Fabric, the correct subcommand to add a peer to a channel is peer channel join. This

command is used by a peer node to join an existing channel. The command requires a block to be

specified which typically is the genesis block of the channel, allowing the peer to synchronize with

the channel's ledger from the beginning. Other commands like peer channel fetch, peer channel

create, and peer channel update serve different purposes. peer channel fetch retrieves blocks from a

channel, peer channel create is used to set up a new channel, and peer channel update modifies

channel settings. Thus, peer channel join is the specific command used to connect a peer to a

channel​​.

For a test network in Hyperledger Fabric, one ordering node is sufficient to form an Ordering

Service7. The test network typically uses a single-node Raft ordering service for simplicity and

educational purposes.​However, for production networks, a multi-node ordering service is

recommended for fault tolerance and high availability8.

In Hyperledger Fabric, certificates primarily provide identity for various actors within the network,

such as peers, orderers, and clients. These certificates facilitate not just node-to-node

communication and data integrity but also contribute significantly to the security measures of the

network, such as authentication and authorization processes. Importantly, these certificates are

utilized in TLS (Transport Layer Security) protocols to secure communications between nodes on the

network. Fabric utilizes X.509 certificates for these purposes, which are issued by a Certificate

Authority (CA) within the network .

The Operations Service API hosted on the HTTP server by the peer and the orderer in Hyperledger

Fabric does not provide the functionality to set the log level. This API is primarily designed to offer

operational insights and controls like retrieving log data, fetching metrics, and performing health

checks. The ability to dynamically adjust the log level via this API is not supported, as logging levels

are typically configured statically through configuration files or environment variables at the time of

node startup. This design helps maintain the integrity and stability of the operational log data​​.

The​idemixgen​tool is used to create configuration files for the Identity Mixer based MSP

(Membership

Service

Provider)

in

Hyperledger

Fabric.​When

configuring

membership,

the​idemixgen​tool creates three directories:​/ca/,​/msp/, and​/user/1. The​/ca/​directory contains

the issuer secret key, issuer public key, and revocation key, which should only be present for a

Certificate Authority (CA). The​/msp/​directory contains the issuer public key and revocation public

key, which are required to set up an MSP that verifies Identity Mixer signatures.​The​/user/​directory

specifies a default signer configuration1. Therefore, the correct answer is the user directory, which is

created alongside the ca and msp directories by the​idemixgen​tool.

In Hyperledger Fabric, an endorsement policy specifies which network participants, identified by

their digital identities, must endorse a transaction before it can be considered valid. This is crucial for

the network's security and integrity, as it controls how transactions are approved and added to the

ledger. Endorsement policies are part of the channel configuration and can be customized to fit the

specific needs of a business network. They dictate the necessary endorsements from specific

organizations or even particular roles within those organizations, ensuring that only authorized

entities can validate transactions. This mechanism supports the collaborative yet secure nature of

the enterprise blockchain, where trust is decentralized across different organizations that are part of

the network​​.

For an endorsed transaction, the gateway service forwards the transaction to the ordering service.

The ordering service then packages this transaction with other endorsed transactions into a block.

This block is subsequently distributed across the network to all peers for validation and commitment

to the ledger. The ordering process ensures the maintenance of transaction order across the

network, crucial for the consistency and integrity of the blockchain .

In Hyperledger Fabric, inter-contract communication is possible both within the same channel and

across different channels. However, the functionality to alter the state (using PutState) of a

chaincode on a different channel is restricted. This limitation is due to the security and isolation

principles of channels in Hyperledger Fabric, where each channel represents a separate ledger and

state. Transactions within a channel can read and write data freely, subject to endorsement policies,

but writing data to another channel's chaincode directly is not permitted. This prevents unauthorized

influence on a separate and potentially isolated business process, ensuring that operations within a

channel are controlled and secure​​.

In Hyperledger Fabric, signature policies specify the identities of specific users who must sign a transaction for it to be considered valid. These policies define the endorsement rules associated with a chaincode and are a critical component of the transaction flow. They ensure that transactions are endorsed by the correct entities as stipulated by the governance of the network. Signature policies are not related to the number of nodes, private keys of participants, or the type of consensus algorithm used but are strictly about defining which users or member organizations' signatures are required to fulfill transaction criteria​​.

The last step in the Hyperledger Fabric transaction flow is the commitment of the transaction to the

ledger and the subsequent notification to the client application1. Once the transaction has been

endorsed and ordered, it is committed to the ledger on all peers. After the transaction is committed,

the peers asynchronously notify the client application of the success or failure of the transaction.​This

ensures that the client application is aware of the outcome and can take appropriate actions based

on the result of the transaction1