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How do I use feature flags in a multi-tenant Node.js app?
Give the flag provider enough context to evaluate the request for the right entity. LaunchDarkly’s Node.js server-side SDK is designed for multi-user server applications and evaluates a flag using a context passed to the client method. A context identifies an entity by kind and key; contexts are scoped to a LaunchDarkly project and environment. The appropriate context depends on what your rules target.
Choose the context that matches your targeting rules
- Tenant targeting: represent a tenant as an organization context, or use another stable context kind chosen for your system. Use a durable tenant key rather than a display name that can change.
- User targeting: include a user context when rules need to distinguish people within a tenant.
- Both tenant and user targeting: use a multi-context so a rule can evaluate more than one entity kind together. LaunchDarkly documents organization contexts and multi-contexts for this purpose.
Build the tenant context from trusted authenticated request state—for example, the tenant resolved by your authentication and authorization layer—not from a tenant key accepted directly from an untrusted request parameter. A flag context supplies targeting information; it does not prove that the caller may access that tenant.
Keep flag evaluation downstream of identity resolution
- Authenticate the request and resolve the caller’s permitted tenant using your normal security controls.
- Construct the evaluation context from that trusted identity, adding user or other entity details only when the targeting rules need them.
- Evaluate the flag with an intentional fallback value and use the result to choose application behavior.
- Continue checking permissions and scoping every tenant data query independently of the flag result.
LaunchDarkly’s OpenFeature provider guide documents a provider-neutral Node.js setup using the OpenFeature server SDK and the LaunchDarkly server SDK/provider. It shows awaiting provider setup with OpenFeature.setProviderAndWait(...), obtaining a client, then evaluating with a fallback and context. The provider guide specifies a targeting key for the LaunchDarkly context and supports context kinds, including organization as an example. Its stated compatibility is OpenFeature Node.js SDK v1.x and Node.js 18 and above; verify compatibility and APIs for the versions you select before adopting an example.
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What happens to feature flags when the SDK is unavailable?
Evaluation behavior depends on the provider, SDK state, and any configured stores. Do not assume an unavailable provider will return a current value, or that a cache guarantees availability. Decide what the application should do when the SDK is not ready or evaluation cannot use current provider data, and supply a fallback for each flag.
Choose a fallback by the consequence of each behavior
LaunchDarkly recommends providing fallbacks, reviewing them periodically, and generally preferring a stable behavior that keeps the application running. For high-security or compliance-related functions, a more restrictive behavior may be appropriate. There is no universally safe “on” or “off” fallback: the right choice depends on what each flag controls.
Rank #2
| Flag purpose | Question to answer | Operational record |
|---|---|---|
| Ordinary product behavior | Which known-working behavior should continue if evaluation is unavailable? | Baseline behavior, consequence of enabling or disabling it, owner, and review date |
| Security- or compliance-sensitive behavior | Would enabling the feature during an outage be less safe than disabling it, or would disabling it create another unacceptable risk? | Chosen restrictive or stable behavior, risk rationale, owner, and review date |
Record the fallback alongside the flag’s purpose and revisit it when the feature’s behavior or risk changes. Remove obsolete flags rather than leaving old fallback decisions and targeting rules in place indefinitely. Test the application’s degraded behavior with the SDK not ready and with the provider or backing store unavailable; the specific tests and incident policy are decisions for your service, not universal vendor defaults.
Should I cache feature flags in Redis?
Redis can persist feature data for a supported provider integration, but it is not a blanket requirement for feature flags or a guarantee of fresh values. Identify which component owns each cache and what happens when its upstream source is unavailable before adding another layer.
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Rank #3
| Layer | What it represents | What to verify |
|---|---|---|
| SDK in-process state | Data available to the running application process for evaluations. | How the selected SDK version receives updates and behaves when it is not ready or cannot reach its provider. |
| Redis feature store | Persistent feature data used by a provider integration that supports Redis. | Redis availability, the deployed integration’s read/write behavior, and recovery when Redis or the provider is unavailable. |
| Integration’s local in-memory cache | In the LaunchDarkly-maintained node-server-sdk-redis integration, a cache that can retain last-known data for a configurable period. |
The repository documents this cache as enabled by default and cacheTTL: 0 as the setting to turn it off. Confirm behavior for the exact integration version you deploy. |
| Application-level cache | An additional cache added by your service outside the SDK/store integration. | Its keying, expiry, invalidation, and behavior during flag changes or failures; do not assume the SDK manages it. |
Retaining last-known data can reduce reads to Redis, but can also delay propagation of a change or preserve old values after an upstream failure. The cited integration documentation does not establish a universal staleness window or incident policy. Measure propagation in your deployed setup, and exercise provider and Redis failure paths before relying on a particular cache configuration. The cited Redis defaults are specific to that LaunchDarkly integration; they should not be generalized to other providers, SDKs, or package versions.
How do I audit feature-flag changes?
Use the provider’s audit history to investigate configuration changes, and use application telemetry to investigate which decision a particular request received. These answer different questions.
Rank #4
Configuration history: who changed what, and when?
LaunchDarkly’s Audit Log documentation states: “LaunchDarkly maintains a record of all the changes made to any resource in the system.” It describes access through the audit-log API, including timestamp filtering or a custom policy, and through the product UI’s Change history. Use that history to examine changes to flag configuration, subject to the access and history available in your account.
Request-level evidence: what happened for this tenant?
An audit log of resource changes should not be treated as a record of every evaluation or tenant request. For incident investigation, add application-level logging or tracing appropriate to your privacy and retention policies. Useful fields can include:
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- Request or trace ID.
- A minimized or pseudonymized trusted tenant identifier, where appropriate.
- Flag key and evaluated variation.
- Whether evaluation used a fallback or encountered an error.
- SDK/provider readiness or relevant failure state.
- Relevant release or configuration version, if available and useful in your system.
Avoid putting personal or sensitive tenant data in flag keys or logs without a data-minimization review. Correlating a request trace with the provider’s change history can help distinguish a configuration change from a request-specific evaluation or application failure.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When should I use OpenFeature rather than a provider-specific SDK?
OpenFeature can decouple application code from a particular flag provider. Its Node.js server SDK documents hooks, transaction context propagation, tracking, shutdown, and multi-provider strategies. This can help when an application needs a provider-neutral API or is planning migration, comparison, or hybrid use.
A provider-neutral API does not guarantee identical evaluation semantics across providers or effortless failover. OpenFeature’s multi-provider strategy supports scenarios such as backup, comparison, hybrid use, and migration, but the behavior must be verified for the selected providers and strategy. A provider-specific SDK may expose provider-specific capabilities directly; weigh that against the coupling and operational work involved in changing providers.
LaunchDarkly’s Node.js and OpenFeature documentation can change. Check the package compatibility, provider behavior, API details, and account access against the exact versions and deployment you operate.
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