Enabling Fleet and Polly on self-hosted LangSmith after v0.15 upgrade

Last updated: July 1, 2026

Symptom

Upgrading a self-hosted LangSmith control plane to v0.15 via Helm fails when fleet.enabled: true is set without providing an encryption key:

Error: UPGRADE FAILED: execution error at (langsmith/templates/validate.yaml:266:4):
fleet.encryptionKey is required when fleet.enabled is true
(not needed if config.existingSecretName is set with the key already present)

Triggering command:

helm upgrade langsmith langchain/langsmith --version 0.15.0-rc.13 \
  --namespace default \
  --values /tmp/langsmith-values-updated.yaml

Polly has the same pattern and needs its own separate key.

Cause

The LangSmith Helm chart validates at langsmith/templates/validate.yaml line 266: when fleet.enabled is true, fleet.encryptionKey must be set, unless a pre-existing Kubernetes secret referenced via config.existingSecretName already contains the key. Polly enforces the same rule for its own key. Enabling the feature flag without setting the key hits this gate on helm upgrade.

Resolution

1. Generate encryption keys

Each feature needs a distinct key:

# Fleet
openssl rand -hex 32

# Polly
openssl rand -hex 32

2. Add the keys to Helm values

Option A, inline in values YAML:

fleet:
  enabled: true
  encryptionKey: "<output of openssl command>"

polly:
  enabled: true
  encryptionKey: "<output of openssl command>"

Option B, reference a pre-existing Kubernetes secret (avoids plaintext in values files):

config:
  existingSecretName: "<your-secret-name>"

The secret must contain the keys the chart expects for Fleet and Polly.

3. Re-run the Helm upgrade

helm upgrade langsmith langchain/langsmith --version 0.15.0-rc.13 \
  --namespace default \
  --values /path/to/updated-values.yaml

The validation passes once the key is present.

Upgrade path from v0.13.x

Upgrade one minor version at a time so you don't skip database migrations:

  1. v0.13.x to v0.14.latest (for example v0.14.6). v0.14 added a queue-ingestion pod that improves trace ingestion latency.

  2. v0.14.x to v0.15.0 (latest RC or stable).

Take backups before each step. Expect brief downtime per upgrade due to database migrations.

Control plane vs. data plane

Fleet and Polly are control-plane features. If the control plane and data plane are in separate accounts or clusters, apply the Helm changes to the control plane only. The data plane does not need changes for these features.

LangSmith Engine availability

LangSmith Engine (also called the Agent Builder engine) is not yet available on standard self-hosted Kubernetes deployments. It is available on BYOC deployments, with a general self-hosted rollout planned around August 2026. Confirm the current timeline with the account team.

References