High Availability Setup Guide

For zkSync Era, a single-node deployment represents a critical point of failure. The main node is responsible for tracking the L2 state, sequencing transactions, and interacting with the L1 smart contracts. If this node fails, an exchange's ability to monitor deposits, process withdrawals, or broadcast transactions stops. The External Node (EN), while designed for read scaling, is not a simple drop-in replacement for a failed main node without a deliberate failover architecture. Operators who treat the EN as a passive replica without formalizing leadership election and state verification risk serving stale data or halting operations during an upgrade or crash.

A production-grade HA setup for zkSync Era must address three distinct failure domains. Main node failover requires a standby instance with a replicated database that can assume block production or L1 interaction duties without causing a chain fork or double-signing. EN load balancing demands a topology where multiple EN instances serve API traffic behind a layer-7 proxy, with health checks that can detect a node falling out of sync and drain it from the pool before it serves incorrect data. Prover redundancy is essential for ZK Stack deployments where proof generation is on the critical path for finality; a stalled prover can delay L1 settlement and freeze bridge withdrawals. Each layer requires distinct monitoring signals—block height lag, proof generation queue depth, and L1 gas price volatility—to trigger automated failover without manual intervention.

The operational risk is compounded during network upgrades. A mandatory protocol upgrade that changes the state transition function or system contracts can cause nodes running different versions to diverge. An HA setup without a tested rollback and re-sync procedure can turn a routine upgrade into a prolonged outage. Chainscore Labs designs and reviews HA architectures specifically for zkSync Era production deployments, ensuring that failover logic, database replication, and monitoring are validated against the protocol's actual failure modes—not generic Kubernetes patterns.

Designing a high-availability (HA) setup for zkSync Era requires modeling the protocol's architecture as a set of distinct, loosely coupled failure domains. A failure in one domain must not cascade into another, and each domain requires its own redundancy strategy. The primary domains are: the L2 sequencer and block production pipeline, the state synchronization and External Node (EN) read layer, the prover subsystem responsible for generating validity proofs, and the L1 interaction layer that manages data availability and proof settlement on Ethereum.

The sequencer domain is the most critical for liveness. A failure here halts L2 block production. HA strategies involve active-passive or active-active main node configurations with automated failover based on L1 contract monitoring and health checks. The EN domain is stateless in terms of block production but stateful for serving API traffic. It scales horizontally behind a load balancer, but operators must manage WebSocket subscription affinity and ensure all instances are synchronized to within a safe lag tolerance to prevent serving stale data. The prover domain is computationally intensive and operates asynchronously. Redundancy is achieved by running multiple prover instances, but operators must implement locking or leader-election mechanisms to prevent duplicate proof submissions that waste L1 gas.

The L1 interaction domain is a shared dependency. The zkSync Era main node must maintain a reliable connection to an Ethereum execution client to monitor the bridge contract, publish state diffs, and settle proofs. An HA design must account for L1 client failover and manage nonce continuity for L1 transactions. Chainscore Labs can review a team's HA architecture against these specific failure domains, identifying single points of failure in sequencer failover logic, EN synchronization gaps, prover coordination, or L1 relay strategies before they cause a production outage.