Transient outages, upstream faults, and service instability events.
Last reviewed: February 13, 2026|27 mapped errors|Page 2 of 2
Availability errors indicate that service execution failed or upstream dependencies could not complete in time for the current request path.
Provider-specific error pages mapped to this category (27 total). Showing 16-27.
HTTP 451 Unavailable For Legal Reasons means access is denied due to legal demands or legal policy constraints.
HTTP 500 Internal Server Error means the server encountered an unexpected condition while processing the request.
HTTP 501 Not Implemented means the server does not support the functionality required to fulfill this request.
HTTP 502 Bad Gateway means a gateway or proxy received an invalid response from an upstream server.
HTTP 503 Service Unavailable means the server is temporarily unable to handle the request due to overload or maintenance.
HTTP 504 Gateway Timeout means a gateway or proxy did not receive a timely response from an upstream server.
HTTP 505 HTTP Version Not Supported means the server does not support the major HTTP version used in the request.
HTTP 506 Variant Also Negotiates means transparent content negotiation is misconfigured and selected variants are themselves negotiable.
HTTP 507 Insufficient Storage means the server cannot store the representation needed to complete this request.
HTTP 508 Loop Detected means the server found an infinite loop while processing recursive or depth-based operations.
HTTP 510 Not Extended is an obsolete status code from an experimental extension model and should not be emitted by modern HTTP APIs.
HTTP 511 Network Authentication Required means the client must authenticate to gain network access, often through a captive portal.
Compare Guide
Use 429 for caller-specific throttling and 503 for service-wide outages, so retry behavior, escalation paths, and incident ownership stay correct.
Compare Guide
Debug 500 vs 502 faster: use 500 for origin failures and 502 for invalid upstream responses at gateways, then route incidents to the right team.
Compare Guide
Fix upstream errors faster: use 502 when a gateway gets an invalid upstream response, and 504 when the upstream service exceeds your timeout budget.
Playbook
Use this playbook to separate invalid upstream responses from upstream wait expiration and deadline exhaustion, and apply timeout budgets, safe retries, and circuit-breaker controls safely.
Playbook
Use this playbook to separate origin-side 500 failures from temporary 503 dependency or capacity outages, then apply safe retry and escalation paths.
Playbook
Triage 500, gRPC UNKNOWN, and cloud InternalError fast: preserve correlation IDs, separate transient provider faults from app bugs, and apply safe retries.
500 indicates internal server failure, 502 indicates invalid upstream response, 503 indicates temporary unavailability, and 504 indicates upstream timeout.
Retries worsen outages when they are unbounded or synchronized, because they increase load on already degraded dependencies.
Sustained normalization of error rate and tail latency under representative traffic, not only short success bursts.