500 Internal Server Error vs 503 Service Unavailable

500 indicates unexpected code/runtime failure. 503 indicates temporary unavailability with recovery intent.

Aspect	500 Internal Server Error	503 Service Unavailable
When it happens	Emitted when conditions specific to 500 internal server error occur.	Emitted when conditions specific to 503 service unavailable occur.
How to tell apart	Identify which layer emitted the code and inspect headers/logs for that layer.	Confirm whether problem is auth/policy, upstream quality, overload, or timeout.
Troubleshooting first step	Trace request ID through edge and application logs.	Check deploy/config changes and dependency health in same time window.
Practical note	Do not mask this response with generic handlers.	Return explicit headers like Retry-After or auth challenge when relevant.

When each appears in production

Use CDN/proxy logs to find emission point, then app logs/traces to isolate root cause.

Validate routing, policy, and timeout budgets in order. Fix the first failing layer before tuning client retries.