What is an RPC Node, and How Does it Work?

Blockchain technology has transformed the way we think about data storage and transfer. At its core, a blockchain is a decentralized network of nodes that communicate with each other to validate and record transactions on an immutable ledger.

At the heart of every blockchain's functionality is the ability to reliably interact, read, and write data. A critical component that enables this communication between nodes is RPC (Remote Procedure Call) nodes. In simple terms, RPC nodes act as messengers facilitating requests and responses between nodes on a blockchain network. They allow applications and services built on blockchains to read chain data and submit transactions.

Despite their essential role as intermediaries for blockchain data transactions, RPC nodes often remain poorly understood behind the scenes. This article aims to shed light on these unsung heroes powering blockchain interoperability and data accessibility. It will provide a comprehensive overview of RPC nodes, dissecting their anatomy, functionality, limitations, challenges, and real-world significance. The goal is to provide a comprehensive overview of RPC nodes and how they enable various interactions within blockchain networks.

Understanding Blockchain Nodes

A node is a fundamental component of blockchain networks that stores a copy of the blockchain ledger and helps maintain the network. Nodes are responsible for validating, broadcasting, and relaying transactions across the network. Different types of nodes serve various functions:

Full nodes

Full nodes store a complete copy of the blockchain ledger and verify all transactions and blocks on the network. They have significant storage capacity and bandwidth to operate. Full nodes independently validate all transactions and blocks, acting as a source of truth for the network.

Light nodes

Light nodes store a partial copy of the blockchain and rely on full nodes to verify transactions and blocks. They have lower hardware requirements than full nodes but cannot independently validate the entire blockchain state.

Archival nodes

Archival nodes are enhanced full nodes that, in addition to the entire blockchain ledger, maintain a complete archive of historical blockchain data, including old unused accounts, spent transactions, and other metadata. Archival nodes allow users to query detailed historical data.

Mining nodes

Group and validate transactions into blocks and add them to the blockchain. They also produce new cryptocurrency through mining.

Master nodes

Master nodes provide special functions like increased privacy and instant transactions. They require a collateral stake to operate.

The decentralized nature of blockchain stems from this peer-to-peer network of nodes. Instead of a central server, the nodes collectively power the network by contributing computing resources. Each node stores a copy of the ledger and participates in transaction validation and block creation, eliminating the need for centralized control.

The distributed consensus mechanisms ensure all nodes stay in sync while updating the blockchain ledger. New blocks propagate through the network as each node communicates with peers, enabling the blockchain's resilience and security without centralized servers.

What Makes Remote Procedure Call (RPC) Nodes Unique?

RPC nodes play a unique and crucial role in blockchain networks. Unlike full nodes, which store and validate the entire blockchain, or light nodes, which only store block headers, RPC nodes act as a bridge between a blockchain and applications external to the network.

RPC refers to a protocol allowing a program on one computer to execute a program or function on another. The requesting program is called the client, while the computer running the requested program is called the server.

The core purpose of an RPC node is to facilitate read and write operations on the blockchain by exposing an API for applications to interact with. This function allows external programs to query data from the blockchain and submit transactions without running a full node themselves.

RPC nodes enable applications to retrieve information like account balances, smart contract data, transaction details, and more through API calls. Developers can leverage RPC nodes to build decentralized applications that can read blockchain data without running an entire node.

Defining RPC

RPC is a protocol that allows a computer program to execute code or procedures on another computer over a network. With RPC as a local function, a client program can call methods or procedures on a server program. The underlying network communication details are abstracted away.

RPC works by the client sending a request message to the server, which then processes the request and returns a response. This allows for seamless integration between the client and server applications. The client is unaware of the specifics of network communication.

The JSON-RPC protocol is commonly used for blockchain applications to enable RPC calls over the web. JSON-RPC allows remote procedure calls to be encoded in JSON format for transmission over HTTP, providing a simple yet robust mechanism for external applications to interact with the blockchain network.

With JSON-RPC, the client sends a request object to the RPC server node, containing the method name to call and any required parameters. The server processes this and returns a JSON response object with the result, error information, or any other data the client needs. JSON-RPC has become a standard for many blockchain platforms and tools.

The Anatomy of an RPC Node

An RPC node consists of several vital components that enable it to facilitate communication between a blockchain network and external applications. At its core is the node software that allows it to connect to the peer-to-peer network and synchronize a local copy of the blockchain.

Popular node software implementations RPC nodes use include Bitcoin Core, Geth for Ethereum, Parity (OpenEthereum), Neo CLI, and Ripple Rippled. The node software enables standard node functions like transaction validation and block verification. In addition, RPC nodes run software that exposes an RPC server and allows HTTP connections. Some examples include:

• Bitcoin Core's built-in HTTP RPC server.

• Web3.js library for Ethereum nodes.

• JSON-RPC server implementations like jsonrpc-jsonrpc.

These software components allow external applications to make RPC calls to the node via HTTP and transmit requests in a standard JSON-RPC format.

The node then parses the JSON payload, executes the requested operation, and returns the response back to the caller. Common RPC methods exposed include commands to retrieve blockchain data, submit transactions, and interact with smart contracts.

When an RPC request comes in, the node handles it via the following lifecycle:

• The HTTP server receives the incoming request.

• The JSON payload is parsed and validated.

• The underlying node software executes the requested operation.

• Any errors are caught and handled.

• The response payload is formatted into JSON.

• The HTTP server returns the JSON response to the client.

The diagram below illustrates the lifecycle of an RPC request:

The node bridges the raw blockchain protocol and application developers by exposing this RPC interface. The node manages all the underlying blockchain communication and data retrieval, enabling developers to focus on their app logic and user experience.

Initiating the RPC Call

An RPC call begins when a client application initiates a request to a blockchain network's RPC node. The client constructs an RPC request in JSON-RPC format containing a method name and any parameters needed.

For example, to request the current block number in Ethereum, the JSON-RPC request would be:

json

{
	"jsonrpc": "2.0",
	"method": "eth_blockNumber",
	"params": ["0x1b4", true],
	"id": 1
}

The key components are:

• jsonrpc: The JSON-RPC version used

• method: The RPC method to call, e.g. eth_blockNumber

• params: Any parameters for the method call (optional)

• id: A unique identifier for the request

The request data is packaged into an HTTP POST request and sent to the RPC node's endpoint URL. Another common RPC call example includes the request to get the balance of an account:

json

{
	"jsonrpc": "2.0",
	"method": "eth_getBalance",
	"params":["0xAccountAddress", "latest"],
	"id": 1
}

The client initiates an RPC call by formatting a JSON-RPC request object containing the method name and parameters. This is then transmitted to the RPC node for processing. The node will parse the request, execute it on the blockchain if it is valid, and return a JSON-RPC response to the client.

Processing the Request

Once the RPC node receives the request, it needs to process it to execute the desired operation on the blockchain. The request process involves several steps:

1. Parsing the Request: The RPC node will first parse the JSON-RPC request to extract the method name, parameters, and ID, allowing it to understand what the client is asking for.

2. Method Lookup: The node will then determine if the requested method name corresponds to a valid API method available on the node, which ensures the request can actually be executed.

3. Parameter Validation: If the method exists, the node will validate the parameters sent along with the request. Required parameters must be present and of the correct data type to prevent execution errors.

4. Request Execution: The node will execute the request using a valid method and parameters, which could involve reading data from the blockchain or pushing a new transaction.

5. Smart Contract Execution: The RPC node may need to execute a smart contract function to commit a state change to the blockchain for write operations. The node handles mapping the requested operation to the appropriate contract execution.

6. Error Handling: If any validation checks fail, e.g., invalid methods or parameters, the RPC node will return an error immediately without execution. The node should also gracefully handle execution errors.

The RPC node acts as the middleware between the external application and the underlying blockchain, ensuring only valid operations are executed. The structured flow of parsing, validating, implementing, and handling errors allows the node to provide robust access to the blockchain.

Responding to the Call

Once the RPC node has processed the request and executed any relevant operations, it needs to send back the response to the application or client that initiated the call. The node compiles the processing results, whether returned data from a query, a transaction receipt, or an error message.

The RPC node then formats this response according to the protocol being used. JSON-RPC, one of the most common protocols, structures the response as a JSON object that includes the request ID, a result field containing the data, and an optional error field if something goes wrong. Other web-based protocols, like HTTP, use standard response codes and formatting.

The response data itself can take different forms depending on the request method. For simple data queries, it may return the requested information, such as account balances or contract states. For write operations like sending transactions, it provides transaction receipts and hashes. The RPC node is responsible for adequately encoding this data, like hex-encoding binary transaction hashes.

Once formatted, the RPC node sends the response back to the client using the same underlying TCP/IP and transport layer connections, thus completing the request-response cycle, enabling the external application to take the returned data and act on it or display it to users. The whole process allows seamless communication between off-chain applications and the blockchain network.

Understanding RPC Endpoints

RPC endpoints are specific entry points for accessing a blockchain network, functioning as gateways facilitating interactions between external applications or users and the blockchain's functionalities. These endpoints allow for the execution of read and write operations on the blockchain, enabling the creation and interaction with decentralized applications, smart contracts, and more. There are primarily two types of RPC endpoints:

Public RPC Endpoints

These are externally accessible gateways to a blockchain network, allowing developers, applications, and users to interact with the blockchain's functionalities. Public RPC endpoints are available, enabling broad participation and integration with the decentralized ecosystem. Such accessibility is more than a convenience—it forms the backbone of a participatory and integrative decentralized environment. They serve as a communal resource that allows:

• Broad access for community engagement.

• Quick and easy integration for developer projects.

• A gateway for decentralized applications to communicate with the blockchain.

Private RPC Endpoints

Unlike public ones, private RPC endpoints are accessible only through private or virtual private networks (VPNs). They are often used for more controlled and secure interactions with a blockchain network, serving specific applications or organizational needs. Their use-case scenarios usually revolve around the following:

• Ensuring a more secure and controlled environment for blockchain interactions.

• Catering to specific enterprise applications with enhanced privacy requirements.

• Supporting operations that demand a higher level of performance and reliability.

Private endpoints are commonly utilized by organizations that seek to maintain centralized control while leveraging the benefits of blockchain technology.

Tutorial: How to Access RPC Nodes

Accessing RPC nodes involves interacting with a blockchain network to perform actions like reading data or submitting transactions. Here’s a general step-by-step guide on how to do this:

Scalability and Security Considerations

RPC nodes enable external applications to interact with blockchain networks. However, operating RPC nodes has unique scalability and security challenges that must be addressed.

Scalability Issues

As blockchain adoption grows, RPC nodes face increasing demands and traffic, which can lead to bottlenecks that impact performance:

• Throughput limitations: Each RPC node has a limit on how many requests it can handle per second. When overloaded, requests get queued, and latency increases.

• Network congestion: High volumes of RPC traffic can congest network links of nodes, leading to delays.

• Load balancing: The uneven distribution of requests across RPC nodes causes some to be overloaded while others need to be more utilized.

Strategies like clustering, caching, and sharding can be used to handle scalability. Upgrading node hardware also helps by increasing capacity. However, scaling limitations remain a crucial area of improvement for RPC infrastructure.

Security Considerations

Security is a significant concern when it comes to RPC nodes. RPC nodes can be attractive targets for attackers as the conduits for reading and writing data on a blockchain. Some potential attack vectors include:

• Eavesdropping: Attackers may try to intercept RPC commands and data in transit between nodes. Doing this could allow them to steal funds, manipulate data, or degrade services.

• Data injection: Attackers could try to inject malicious RPC commands to corrupt data or trigger unwanted actions. Proper input validation on nodes is essential to prevent this.

• Denial-of-service (DDoS): By flooding nodes with invalid requests, attackers can overwhelm and crash them, preventing legitimate use. Limiting request rates can help mitigate this threat.

• Node impersonation: Attackers may try impersonating an actual node to trick other nodes into connecting and sending sensitive data. Mutual authentication using digital signatures can prevent this.

Mitigating these risks involves firewalls, authentication mechanisms, input sanitization, and isolation of critical wallet functions. Carefully limiting RPC command permissions is also essential. Ongoing monitoring and testing are vital in identifying and patching vulnerabilities.

Conclusion

RPC nodes are necessary for blockchain communication, which links different network nodes. They enable both fundamental interactions, like data reading and writing on the blockchain, and the development of complex blockchain-based services such as wallets, exchanges, NFT platforms, and more. Essentially, RPC nodes bring blockchain technology to life by facilitating transaction processing and data integrity, making them indispensable for the practical application of blockchain.

As blockchain technology continues to be adopted, the role of RPC nodes as critical infrastructure is expected to grow. Despite facing challenges in security and scalability, technological innovations like layered solutions and sharding offer hope for their evolution to meet the demands of increasingly complex decentralized systems.

Understanding RPC node functionality is crucial for anyone looking to leverage blockchain technology. They represent the backbone of current blockchain applications and are pivotal in unlocking the technology's future potential.