前言

最近用istio偵測，常碰到某個服務狀態會掉到80%以下，
那時都有看到APM的程式報錯，但沒人反應，最近有次發生在上班時間，
馬上聯絡同事看他的服務有沒有正常，
最後一路追，
發現狀態碼是回 503 DC ，對這個關鍵字有印象，但常會忘記他的全名。

正文

下列為envoy常見縮寫比對

HTTP and TCP

UH: No healthy upstream hosts in upstream cluster in addition to 503 response code.
UF: Upstream connection failure in addition to 503 response code.
UO: Upstream overflow (circuit breaking) in addition to 503 response code.
NR: No route configured for a given request in addition to 404 response code, or no matching filter chain for a downstream connection.
URX: The request was rejected because the upstream retry limit (HTTP) or maximum connect attempts (TCP) was reached.
NC: Upstream cluster not found.
DT: When a request or connection exceeded max_connection_duration or max_downstream_connection_duration.

HTTP only

DC: Downstream connection termination.
LH: Local service failed health check request in addition to 503 response code.
UT: Upstream request timeout in addition to 504 response code.
LR: Connection local reset in addition to 503 response code.
UR: Upstream remote reset in addition to 503 response code.
UC: Upstream connection termination in addition to 503 response code.
DI: The request processing was delayed for a period specified via fault injection.
FI: The request was aborted with a response code specified via fault injection.
RL: The request was ratelimited locally by the HTTP rate limit filter in addition to 429 response code.
UAEX: The request was denied by the external authorization service.
RLSE: The request was rejected because there was an error in rate limit service.
IH: The request was rejected because it set an invalid value for a strictly-checked header in addition to 400 response code.
SI: Stream idle timeout in addition to 408 response code.
DPE: The downstream request had an HTTP protocol error.
UPE: The upstream response had an HTTP protocol error.
UMSDR: The upstream request reached max stream duration.
OM: Overload Manager terminated the request.
DF: The request was terminated due to DNS resolution failure.