Service unavailable

The Service unavailable error means that a server is currently unable to handle the request. This is a global runtime and network-level error that usually occurs when a service is temporarily overloaded, down for maintenance, or unable to communicate with required upstream components. The Service unavailable error is commonly seen across Linux and Windows servers, Java and Spring Boot applications, Docker containers, cloud platforms, APIs, databases, and load-balanced systems.

When does this error occur?

  • An application server is overloaded and cannot accept new requests
  • A backend service is stopped or restarting
  • A load balancer routes traffic to unhealthy instances
  • A service is intentionally placed in maintenance mode
  • A dependent service such as a database or cache is unavailable

Root cause of Service unavailable

The root cause of Service unavailable is the temporary inability of a service to process requests. This can be due to high CPU or memory usage, exhausted connection pools, crashed processes, failed health checks, misconfigured load balancers, or scheduled maintenance. At the system level, the service is reachable but refuses or cannot handle traffic at that moment.

How to fix the error (step-by-step)

Linux / macOS

Check whether the affected service is running and healthy. 

systemctl status service-name

Restart the service if it is stopped or unresponsive. 

systemctl restart service-name

Review system resource usage to identify overload conditions. 

top

Windows

Verify that the application service is running. 

sc query service-name

Restart the service if required. 

net stop service-name
net start service-name

Java / Spring Boot

Check application logs for startup failures, thread pool exhaustion, or dependency errors. 

server.port=8080
server.tomcat.max-threads=200

Increase thread limits or connection pools only after verifying backend capacity.

Docker / containers

Ensure the container is running and passing health checks. 

docker ps
docker logs container-name

Restart the container if it has crashed or is unhealthy. 

docker restart container-name

Database / network services

Confirm that dependent services such as databases, message queues, or caches are available. 

telnet database-host port

Restore connectivity or restart the dependent service if needed.

Verify the fix

Retry the request after applying the fixes. The service should respond normally instead of returning Service unavailable. Monitor logs, health checks, and system metrics to ensure the service remains stable.

Common mistakes to avoid

  • Restarting services repeatedly without checking logs
  • Increasing limits without fixing resource bottlenecks
  • Ignoring failed health checks in load balancers
  • Assuming the issue is network-related when the service is overloaded
  • Deploying updates without capacity planning

Quick tip

Always configure health checks and alerts so service availability issues are detected before users are impacted.

FAQ

Q: Is Service unavailable the same as server down?

A: No. The server is reachable, but the service cannot handle requests temporarily.

Q: Can high traffic cause Service unavailable?

A: Yes. Traffic spikes can exhaust resources and trigger this error.

Conclusion

Service unavailable indicates a temporary service-side failure. Proper monitoring, capacity management, and dependency checks help prevent this error. For related runtime and system errors, explore more guides on ErrorFixHub.

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