Free Linux Foundation HFCP Practice Exam with Questions & Answers

In Hyperledger Fabric, when executing queries on the ledger, the difference between simple keys and composite keys is significant. Simple keys consist of a single attribute and are straightforward in their use for querying. In contrast, composite keys are formed by combining multiple attributes into a single key, allowing for more complex queries based on multiple fields. Composite keys enable richer, more flexible query capabilities that can facilitate refined searches and analyses within the ledger. This capability is particularly useful in scenarios where a single attribute is not sufficient to uniquely identify ledger entries or when queries need to filter based on multiple criteria​​.

When using "off-line signing" in the Fabric Gateway client API, the cryptographic signature is generated using the message digest. This digest is a hashed representation of the transaction's content, ensuring the integrity and non-repudiation of the transaction as it moves through the Fabric network. This method allows for secure transaction signing without exposing private keys directly on the client-side, aligning with security best practices .

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​​.

Historic states in the Hyperledger Fabric ledger are immutable, meaning they cannot be altered after they have been committed to the ledger. This immutability ensures the integrity and traceability of all transactions on the network. Once a transaction is recorded, it is permanent, and its history can be audited to trace back all operations affecting any piece of data. This feature is fundamental in blockchain technology, providing a verifiable and tamper-evident record. The immutability of historic states is a key component of the trust and security model in Hyperledger Fabric, contrary to options that suggest these records can be modified or are inaccessible​​.

Recovering from a failed migration from Kafka to Raft in Hyperledger Fabric involves restoring the state from a backup. This is necessary because once the ordering service is migrated to Raft and begins committing transactions, reverting to Kafka is not supported without a previous backup. If a migration is botched, and a backup was made at the appropriate point, administrators can roll back to this backup to restore the system to its pre-migration state .

In Hyperledger Fabric, when a transaction that includes thedelState("A")function is committed, it results in the removal of the state of the key "A" from the current state database. However, the history of all transactions that have affected the key "A" remains intact in the ledger. This operation ensures that while the current state reflects the deletion, the immutability and traceability of the ledger are preserved, allowing for auditability and verification of past states. Options such as setting an empty value to the key or altering the transaction history are not supported, as they would violate the principles of immutability and transparency central to blockchain technology. Therefore, the correct outcome of adelState("A")operation is that the current state of "A" is deleted, but its transaction history remains accessible in the ledger​​.

Chaincode in Hyperledger Fabric is essentially smart contract software that defines assets and the transaction instructions for modifying these assets on the ledger. Chaincode functions as the business logic layer of the network, where the rules for interacting with the ledger are specified. It is executed on the network peers and is used to encode the policies and constraints associated with asset exchanges or updates within the business network. This setup allows organizations to automate processes and enforce consistency and compliance across transactions​​.

In Hyperledger Fabric, inter-contract communication is possible both within the same channel and across different channels. However, the functionality to alter the state (usingPutState) 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​​.

When using LevelDB as the state database in Hyperledger Fabric, there is no specific schema that the data stored in the ledger needs to adhere to. LevelDB is a key-value store, which does not enforce any schema on the data it holds. This flexibility allows applications to define their own formats and structures for the data they store, which can vary from simple strings and numbers to more complex serialized data structures. This schema-less nature of LevelDB enables developers to implement the data handling that best suits their application's needs without the constraints of a predefined database schema​​.

In Raft, configuration occurs at two levels: local and channel. The local configuration pertains to node-specific settings such as TLS communication and file storage. The channel configuration, on the other hand, defines the membership and operational parameters of the Raft cluster for a specific channel, including settings like heartbeat frequency and leader timeouts. This dual-level configuration allows for precise control over the behavior of Raft nodes within the Hyperledger Fabric network .