Status Endpoint

A status endpoint is a dedicated API endpoint, typically a URL like /health or /status, that returns a machine-readable response indicating the operational health of a service or application. Its primary function is to provide a standardized way for automated systems—such as load balancers, container orchestrators (e.g., Kubernetes), and monitoring tools—to perform health checks and determine if the service is ready to receive traffic, is alive, or is functioning correctly. The response is usually a simple JSON or plain-text payload containing key status indicators.

The typical response from a status endpoint includes a high-level status code (e.g., OK, ERROR, WARNING) and often granular details about dependencies. These dependencies can include the connectivity to critical downstream services like databases (e.g., PostgreSQL, Redis), message queues, other internal APIs, or external third-party services. By checking these components, the endpoint provides a holistic view of system health beyond just the web server being online, enabling more intelligent routing and alerting in distributed architectures.

Implementing a status endpoint is a core practice in building resilient systems. In microservices and cloud-native environments, infrastructure tools rely on these endpoints for critical operations. For example, a Kubernetes readiness probe polls the endpoint to decide when to add a pod to the service load-balancing pool, while a liveness probe determines if a container needs to be restarted. This decouples infrastructure logic from application logic, allowing for automated recovery and ensuring end-users are only directed to fully functional service instances.

Beyond basic uptime, advanced status endpoints can expose performance metrics and deployment information. They might report on current resource utilization (CPU, memory), cache hit rates, queue depths, or the version of the deployed application. This turns the endpoint into a lightweight diagnostic tool for developers and SREs. For public APIs, a status endpoint is often part of a broader status page (e.g., status.example.com) that aggregates health data from all services to provide transparency to API consumers about ongoing incidents or maintenance.

When designing a status endpoint, key considerations include its performance (it must be fast and low-overhead to avoid false negatives), security (it should not expose sensitive system data), and accuracy (it must perform meaningful checks, not just return a static 200 OK). A well-implemented status endpoint is a foundational component of observability, acting as the first line of defense in detecting and mitigating system failures before they impact users.

A status endpoint is a specific URL, often /status or /health, that returns a machine-readable response detailing the operational state of a service, such as a blockchain node, database, or API server. When queried, it performs a series of internal checks—verifying database connectivity, external API dependencies, system resource usage (CPU, memory), and the status of critical internal processes. The response typically includes a status code (e.g., HTTP 200 for OK, 503 for Service Unavailable), a status indicator ("healthy", "degraded", "unhealthy"), and a timestamp. This allows automated monitoring systems, like uptime robots or orchestration platforms (Kubernetes), to detect failures without manual intervention.

The endpoint's response is often formatted as JSON for easy parsing, containing key-value pairs that offer granular insight. For example, a blockchain node's status endpoint might report the current block height, peer count, sync status, and latency of connected services. This granular data is crucial for system operators and DevOps teams to perform root cause analysis during an incident. By checking which specific component is failing (e.g., "database: unhealthy"), teams can quickly isolate and address the problem, reducing mean time to resolution (MTTR). The endpoint should be lightweight, requiring minimal system resources to generate its response to avoid impacting the primary service's performance.

Implementing a status endpoint follows best practices for reliability and security. It should be publicly accessible for monitoring but may exclude sensitive internal data. For complex systems, a liveness probe confirms the service is running, while a readiness probe indicates it can accept traffic. In microservices architectures, a central status dashboard often aggregates data from all service endpoints, providing a unified view of system health. This mechanism is foundational for building resilient systems, enabling features like automatic failover, where unhealthy instances are removed from a load balancer's rotation, and canary deployments, where new versions are monitored for stability before full release.

The credentialStatus property is an optional field within a Verifiable Credential (VC) that provides a mechanism to check the current validity state—such as revocation or suspension—of the credential without requiring the issuer to re-sign or re-issue it. This property typically contains a type (e.g., StatusList2021, RevocationList2020) and a statusPurpose (e.g., revocation, suspension) that defines the check's intent, along with a statusListIndex and a statusListCredential URI pointing to a status list credential hosted by the issuer. By decoupling the credential's cryptographic proof from its status, this property enables efficient, privacy-preserving revocation checks.

The core mechanism involves a status list, a specially constructed Verifiable Credential maintained by the issuer that contains a bitstring or similar encoded data structure. Each bit in this string corresponds to the status of a single issued credential, indexed by the statusListIndex value. A verifier or holder can fetch this status list credential from the issuer's status endpoint, verify its signature to ensure authenticity, and then check the bit at the specified index. A set bit (e.g., 1) typically indicates a revoked or suspended status, while a cleared bit (0) indicates the credential remains valid. This approach is far more scalable than traditional certificate revocation lists (CRLs) as it allows many credentials to be checked against a single, compact data structure.

Implementing a credentialStatus endpoint requires the issuer to maintain a secure and highly available service. The status list credential itself must be tamper-evident, often achieved through signing with the issuer's Decentralized Identifier (DID) and verification method. Best practices include using content-addressable storage (like IPFS) or publishing the status list credential's hash on a blockchain to provide a persistent, immutable reference. The status list credential should be refreshed periodically, and its issuanceDate should be checked to ensure the verifier is consulting the most recent version. Common implementations include the IETF Status List 2021 specification and the W3C Revocation List 2020 vocabulary.

From a verifier's perspective, checking the credentialStatus is a mandatory step in a robust verification process if the property is present. The verifier must resolve the statusListCredential URI, perform cryptographic verification on the retrieved credential, and then parse the status bitstring. This check ensures that even a cryptographically valid credential with an unexpired validUntil date can be flagged as invalid if the issuer has subsequently revoked it. This process protects against credential misuse, such as when an employee leaves a company or a membership is terminated, providing issuers with ongoing control over the credentials they issue.

The credentialStatus property enables important privacy-preserving features. Techniques like bitstring status lists allow a verifier to check a single credential's status without learning about the status of any other credentials, unlike traditional CRLs which reveal the entire list of revoked entities. More advanced schemes, such as cryptographic accumulators, can offer even greater privacy by allowing a zero-knowledge proof of non-revocation. The choice of status mechanism involves trade-offs between privacy, computational overhead, and implementation complexity, making the credentialStatus property a flexible cornerstone for building trusted, real-world credential ecosystems.