> For the complete documentation index, see [llms.txt](https://docs.zetrix.com/zetrix-l2-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zetrix.com/zetrix-l2-documentation/reliability-and-security/high-availability.md).

# High Availability

## Principles

Z2 HA is built on redundancy, automated failover, health-checked routing, and multi-AZ placement.

## Node Redundancy

* 5 go-quorum QBFT nodes; quorum survives loss of 1 node.
* Public RPC served by multiple nodes behind the NLB; unhealthy nodes auto-removed.

## Validator Redundancy

* 5-member Committee retains quorum through member outages.
* Aggregator role reassignable.

## Sequencer Redundancy

* 3 Sequencer servers: active + standby.
* Fenced, lease-based leadership prevents split-brain.

## Proposer Redundancy

* Current: single Proposer (liveness single point).
* Production: add standby Proposer with leader election. Safety is preserved regardless (Watchers).

## RPC Load Balancer

* AWS NLB with health checks; static endpoint; multi-AZ backends.

## Disaster Recovery

```mermaid
flowchart LR
    subgraph Primary[Primary Region / AZs]
        P[Live cluster]
    end
    subgraph Backup[Backups / Standby]
        B1[(State snapshots)]
        B2[Standby infra]
    end
    P -->|periodic snapshot| B1
    P -->|replicate config| B2
    B1 -->|restore| B2
    B2 -->|failover| Primary
```

* Documented RTO/RPO targets.
* Regular restore drills.

## Backup

| Data                         | Backup method       | Frequency           |
| ---------------------------- | ------------------- | ------------------- |
| Node chain data              | Snapshots           | Daily + pre-upgrade |
| Explorer DB                  | DB backups + WAL    | Continuous/daily    |
| Monitoring config/dashboards | Version control     | On change           |
| Keys/secrets                 | Secure vault backup | On rotation         |

## Monitoring & Alerting

HA is only as good as the alerting that catches degradation early — see [Monitoring](/zetrix-l2-documentation/architecture/system-components.md#monitoring).

| HA element           | Target                     |
| -------------------- | -------------------------- |
| Node fault tolerance | Survive 1 node loss (QBFT) |
| Sequencer failover   | Automatic, fenced          |
| Proposer failover    | Automatic (production)     |
| RPC availability     | Multi-node, multi-AZ       |

***

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