High Availability

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.

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 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.

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:

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:

helm upgrade --install openshell \
  oci://ghcr.io/nvidia/openshell/helm-chart \
  --version <version> \
  --namespace openshell \
  --set supervisor.sandboxRuntime.networkPolicyEnforced=true \
  --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:

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:

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:

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:

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:

helm upgrade openshell \
  oci://ghcr.io/nvidia/openshell/helm-chart \
  --version <version> \
  --namespace openshell \
  --set supervisor.sandboxRuntime.networkPolicyEnforced=true \
  --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.
• To configure automatic certificate renewal, refer to Managing Certificates.
• To configure user authentication and authorization, refer to Access Control.