---
# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: Apache-2.0
title: "High Availability"
sidebar-title: "High Availability"
description: "Run multiple OpenShell gateway replicas on Kubernetes with shared PostgreSQL and authenticated peer routing."
keywords: "Generative AI, Cybersecurity, Kubernetes, High Availability, HA, Gateway, PostgreSQL, Replicas, Failover"
position: 3
---

Run two or more gateway replicas when the OpenShell control plane must remain
available during a gateway pod failure or rolling update. Every replica can
serve API requests. The replicas share persistent state through PostgreSQL and
relay session-bound requests to the replica connected to each sandbox
supervisor.

<Warning>
Gateway replicas do not make PostgreSQL highly available. Use a managed
PostgreSQL service or a separately operated PostgreSQL cluster with its own
backup and failover plan.
</Warning>

## Requirements

An HA gateway deployment requires:

- Two or more schedulable Kubernetes nodes or failure domains.
- PostgreSQL reachable from every gateway pod.
- A Kubernetes Secret in the OpenShell namespace with the PostgreSQL connection
  URI in a key named `uri`.
- `workload.kind: deployment`. The default StatefulSet and per-pod SQLite
  database are intended for a single gateway replica.
- An ingress or load balancer that routes clients to the gateway Service. Refer
  to [Ingress](/kubernetes/ingress) for a Gateway API configuration.

The Helm chart rejects `replicaCount` values above `1` unless
`server.externalDbSecret` is set. It also rejects a multi-replica StatefulSet
unless `workload.allowMultiReplicaStatefulSet` is explicitly enabled. Use a
Deployment for the standard HA configuration.

## Create the PostgreSQL Secret

Provision PostgreSQL outside the OpenShell chart, then create the connection
Secret. The chart does not install PostgreSQL.

```shell
kubectl create namespace openshell

kubectl -n openshell create secret generic openshell-postgres \
  --from-literal=uri='postgresql://openshell:<password>@<postgres-host>:5432/openshell'
```

Use your PostgreSQL provider's required TLS parameters in the connection URI.
Keep the Secret in the same namespace as the gateway release.

## Configure Gateway Replicas

Create `values-ha.yaml`:

```yaml
replicaCount: 2

workload:
  kind: deployment

server:
  externalDbSecret: openshell-postgres

affinity:
  podAntiAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      - labelSelector:
          matchLabels:
            app.kubernetes.io/name: openshell
            app.kubernetes.io/instance: openshell
        topologyKey: kubernetes.io/hostname
```

The anti-affinity rule places the two replicas on different nodes. The
`app.kubernetes.io/instance` value must match the Helm release name. Change the
topology key to a zone label when replicas must span availability zones. A
required rule leaves a replica Pending when the cluster does not have enough
matching failure domains; use preferred anti-affinity when scheduling the
replica is more important than strict separation.

Install or upgrade OpenShell:

```shell
helm upgrade --install openshell \
  oci://ghcr.io/nvidia/openshell/helm-chart \
  --version <version> \
  --namespace openshell \
  --values values-ha.yaml \
  --wait
```

The chart shares its retained sandbox JWT signing material, TLS material, and
default credential-storage encryption key across the gateway pods. Do not
create different copies of those Secrets for individual replicas.

## Verify the Deployment

Wait for all gateway replicas to become ready:

```shell
kubectl -n openshell rollout status deployment/openshell
kubectl -n openshell get pods \
  -l app.kubernetes.io/name=openshell,app.kubernetes.io/instance=openshell \
  -o wide
```

Confirm that the client-facing Service and headless peer Service have ready
endpoints:

```shell
kubectl -n openshell get service openshell openshell-peer
kubectl -n openshell get endpointslice \
  -l app.kubernetes.io/service-name=openshell
kubectl -n openshell get endpointslice \
  -l app.kubernetes.io/service-name=openshell-peer
```

If you changed the chart's generated names with `nameOverride` or
`fullnameOverride`, use the rendered Service names instead.

After registering the gateway with the CLI, verify that requests succeed:

```shell
openshell status
openshell sandbox list
```

## Protect Voluntary Disruptions

Add a PodDisruptionBudget so a voluntary disruption, such as node maintenance,
does not evict every ready gateway pod at once:

```yaml
apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: openshell
  namespace: openshell
spec:
  minAvailable: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: openshell
      app.kubernetes.io/instance: openshell
```

Apply the manifest separately from the OpenShell chart. Match the namespace and
release labels to your installation. A PodDisruptionBudget controls voluntary
evictions; it does not protect against an unavailable node or failure domain.

## How Peer Routing Works

A sandbox supervisor keeps one active control stream to one gateway replica.
That replica records ownership in PostgreSQL. When Kubernetes sends a client
request to another replica, the receiving gateway relays exec, forwarding,
file-sync, service, and status traffic to the owner through the headless peer
Service.

Peer RPCs use a projected, pod-bound ServiceAccount token with the
`openshell-gateway-peer` audience. The receiving gateway validates the token
with the Kubernetes TokenReview API, verifies the live pod identity and release
labels, and authorizes only peer methods. When gateway TLS is enabled, peer
connections also use the chart's TLS materials.

You do not need session affinity at the ingress or client-facing Service.

## Failure and Rollout Behavior

When a non-owner gateway pod stops, Kubernetes removes it from ready Service
endpoints and new requests go to another replica. Existing requests through the
stopped pod disconnect and must be retried.

When an owner gateway pod stops, its connected supervisors reconnect through
the gateway Service and publish new ownership. Other replicas re-read ownership
while waiting to relay a request. A request fails if no fresh, reachable owner
appears before its normal deadline.

Established streams do not move between gateway replicas. An interrupted exec,
forwarding, or service stream must reconnect. File sync retries with a new SSH
session instead of resuming the interrupted byte stream. Rolling updates can
temporarily concentrate supervisor sessions on the replicas that stayed up;
client requests remain routable through peer relay.

## Scale the Gateway

Change `replicaCount` in `values-ha.yaml`, then apply the release again:

```shell
helm upgrade openshell \
  oci://ghcr.io/nvidia/openshell/helm-chart \
  --version <version> \
  --namespace openshell \
  --values values-ha.yaml \
  --wait
```

Keep at least two ready replicas when availability must survive one gateway pod
failure. Size PostgreSQL connection capacity and the cluster nodes for the
selected replica count.

## Next Steps

- To expose the gateway through a highly available data path, refer to
  [Ingress](/kubernetes/ingress).
- To configure automatic certificate renewal, refer to
  [Managing Certificates](/kubernetes/managing-certificates).
- To configure user authentication and authorization, refer to
  [Access Control](/kubernetes/access-control).