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Relayers
Discover the role of relayers in the Wormhole network, including client-side, custom, and Wormhole-deployed types, for secure cross-chain communication.

Relayers

This page provides a comprehensive guide to relayers within the Wormhole network, describing their role, types, and benefits in facilitating cross-chain processes.

Relayers in the Wormhole context are processes that deliver Verified Action Approvals (VAAs){target=_blank} to their destination, playing a crucial role in Wormhole's security model. They can't compromise security, only availability, and act as delivery mechanisms for VAAs without the capacity to tamper with the outcome.

There are three primary types of relayers discussed:

  • Client-side relaying - a cost-efficient, no-backend-infrastructure approach relying on user-facing front ends. It provides a simple solution, although it can complicate the user experience due to the manual steps involved

  • Custom relayers - backend components that handle parts of the cross-chain process, offering a smoother user experience and allowing off-chain calculations to reduce gas costs. These relayers could operate through direct listening to the Guardian Network (Spy relaying)

  • Wormhole-deployed relayers - a decentralized relayer network that can deliver arbitrary VAAs, reducing the developer's need to develop, host, or maintain relayers. However, they require all calculations to be done on-chain and might be less gas-efficient

Fundamentals

This section highlights the crucial principles underpinning the operation and handling of relayers within the Wormhole network.

Relayers are fundamentally trustless entities within the network, meaning while they don't require your trust to operate, you also shouldn't trust them implicitly. Relayers function as delivery mechanisms, transporting VAAs from their source to their destination.

Key characteristics of VAAs include:

  • Public emission from the Guardian Network

  • Authentication through signatures from the Guardian Network

  • Verifiability by any entity or any Wormhole Core Contract

These characteristics mean anyone can pick up a VAA and deliver it anywhere, but no one can alter the VAA content without invalidating the signatures.

Keep in mind the following security considerations around relayers:

  • Trusting information - it is crucial not to trust information outside your contract or a VAA. Relying on information from a relayer could expose you to input attacks

  • Gas optimization - using relayers to perform trustless off-chain computation to pass into the destination contract can optimize gas costs but also risk creating attack vectors if not used correctly

  • Deterministic by design - the design of a relayer should ensure a single, deterministic way to process messages in your protocol. Relayers should have a "correct" implementation, mirroring "crank turner" processes used elsewhere in blockchain

Client-Side Relaying

Client-side relaying relies on user-facing front ends, such as a webpage or a wallet, to complete the cross-chain process.

Key Features

  • Cost-efficiency - users only pay the transaction fee for the second transaction, eliminating any additional costs

  • No backend infrastructure - the process is wholly client-based, eliminating the need for a backend relaying infrastructure

Implementation

Users themselves carry out the three steps of the cross-chain process:

  1. Perform an action on chain A

  2. Retrieve the resulting VAA from the Guardian Network

  3. Perform an action on chain B using the VAA

Considerations

Though simple, this type of relaying is generally not recommended if your aim is a highly polished user experience. It can, however, be useful for getting a Minimum Viable Product (MVP) up and running.

  • Users must sign all required transactions with their own wallet

  • Users must have funds to pay the transaction fees on every chain involved

  • The user experience may be cumbersome due to the manual steps involved

Custom Relayers

Custom relayers are purpose-built components within the Wormhole protocol, designed to relay messages for specific applications. They can perform off-chain computations and can be customized to suit a variety of use cases.

The primary method of setting up a custom relayer is to listen directly to the Guardian Network via a Spy.

Key Features

  • Optimization - capable of performing trustless off-chain computations which can optimize gas costs

  • Customizability - allows for specific strategies like batching, conditional delivery, multi-chain deliveries, and more

  • Incentive structure - developers have the freedom to design an incentive structure suitable for their application

  • Enhanced UX - the ability to retrieve a VAA from the Guardian Network and perform an action on the target chain using the VAA on behalf of the user can simplify the user experience

Implementation

A plugin relayer to make the development of custom relayers easier is available in the main Wormhole repository{target=_blank}. This plugin sets up the basic infrastructure for relaying, allowing developers to focus on implementing the specific logic for their application.

Considerations

Remember, despite their name, custom relayers still need to be considered trustless. VAAs are public and can be submitted by anyone, so developers shouldn't rely on off-chain relayers to perform any computation considered "trusted."

  • Development work and hosting of relayers are required

  • The fee-modeling can become complex, as relayers are responsible for paying target chain fees

  • Relayers are responsible for availability, and adding dependencies for the cross-chain application

Wormhole Relayers

Wormhole relayers are a component of a decentralized network in the Wormhole protocol. They facilitate the delivery of VAAs to recipient contracts compatible with the standard relayer API.

Key Features

  • Lower operational costs - no need to develop, host, or maintain individual relayers

  • Simplified integration - because there is no need to run a relayer, integration is as simple as calling a function and implementing an interface

Implementation

The Wormhole relayer integration involves two key steps:

  • Delivery request - request delivery from the ecosystem Wormhole relayer contract

  • Relay reception - implement a receiveWormholeMessages{target=_blank} function within their contracts. This function is invoked upon successful relay of the VAA

Considerations

Developers should note that the choice of relayers depends on their project's specific requirements and constraints. Wormhole relayers offer simplicity and convenience but limit customization and optimization opportunities compared to custom relayers.

  • All computations are performed on-chain

  • Potentially less gas-efficient compared to custom relayers

  • Optimization features like conditional delivery, batching, and off-chain calculations might be restricted

  • Support may not be available for all chains

Where to Go Next

  • :octicons-book-16:{ .lg .middle } Spy

    Discover Wormhole's Spy daemon, which subscribes to gossiped messages in the Guardian Network, including VAAs and Observations, with setup instructions.

    :custom-arrow: Learn More About the Spy

  • :octicons-book-16:{ .lg .middle } Build with Wormhole Relayers

    Learn how to use Wormhole-deployed relayer configurations for seamless cross-chain messaging between contracts on different EVM blockchains without off-chain deployments.

    :custom-arrow: Get Started with Wormhole Relayers