The phrase "no healthy upstream" means that a system, such as a load balancer or client application, is unable to connect to any functioning backend server or service that it depends on to process requests. In this context, "upstream" refers to the backend servers or services that handle requests. The error usually appears when all backend servers are unreachable, down, overloaded, or failing health checks. This situation prevents the system from routing traffic or fulfilling requests, which can lead to service disruption or downtime. Common causes for "no healthy upstream" include:
- Backend servers being offline or crashing.
- Health checks configured to monitor backend services are failing.
- Network connectivity issues blocking access to backend servers.
- Misconfigurations in routing, load balancer or API gateway settings.
- Resource exhaustion or overload on backend services making them unresponsive.
For example, in an Nginx load balancer setup, this error shows up if none of the configured upstream servers respond properly. In Kubernetes environments, it can indicate that pods are unavailable or not passing readiness checks. In applications like Spotify, it means the device cannot reach Spotify's remote servers due to connectivity or server issues. Troubleshooting involves checking backend server status, network connectivity, logs, and load balancer or health check configurations. Fixes include restarting or repairing backend services, correcting settings, and ensuring servers pass health checks. In summary, "no healthy upstream" means the system cannot find any working backend server to handle its requests, indicating backend server or networking problems that need to be resolved to restore normal operation.