OP Conductor

This page explains what the op-conductor service is and how it works at a high level. To add it to an existing network, follow the setup guide. For the full flag and RPC catalogue, see the configuration and RPC reference.

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Enhancing sequencer reliability and availability

The op-conductor is an auxiliary service designed to enhance the reliability and availability of a sequencer within high-availability setups. By minimizing the risks associated with a single point of failure, the op-conductor ensures that the sequencer remains operational and responsive.

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Assumptions

It is important to note that the op-conductor does not incorporate Byzantine fault tolerance (BFT). This means the system operates under the assumption that all participating nodes are honest and act correctly.

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Summary of guarantees

The design of the op-conductor provides the following guarantees:

• No Unsafe Reorgs
• No Unsafe Head Stall During Network Partition
• 100% Uptime with No More Than 1 Node Failure

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Design

On a high level, op-conductor serves the following functions:

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Raft consensus layer participation

• Leader determination: Participates in the Raft consensus algorithm to determine the leader among sequencers.
• State management: Stores the latest unsafe block ensuring consistency across the system.

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RPC request handling

• Admin RPC: Provides administrative RPCs for manual recovery scenarios, including, but not limited to: stopping the leadership vote and removing itself from the cluster.
• Health RPC: Offers health RPCs for the op-node to determine whether it should allow the publishing of transactions and unsafe blocks.

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Sequencer health monitoring

• Continuously monitors the health of the sequencer (op-node) to ensure optimal performance and reliability.

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Control loop management

• Implements a control loop to manage the status of the sequencer (op-node), including starting and stopping operations based on different scenarios and health checks.

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Conductor state transition

The following is a state machine diagram of how the op-conductor manages the sequencers Raft consensus. Helpful tips: To better understand the graph, focus on one node at a time, understand what can be transitioned to this current state and how it can transition to other states. This way you could understand how we handle the state transitions.

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Next steps

• Follow the setup guide to add op-conductor to an existing multi-sequencer network without downtime.
• Look up flags and admin RPCs in the configuration and RPC reference.
• Checkout op-conductor-mon: which monitors multiple op-conductor instances and provides a unified interface for reporting metrics.
• Get familiar with op-conductor-ops to interact with op-conductor.