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Do not retry indefinitely if service is gone
If there's a call to an external service, saga execution cannot move forward until the result of that call is known, in the sense that Nexus received a result. If there are transient problems, Nexus must retry until a known result is returned. This is problematic when the destination service is gone - Nexus will retry indefinitely, halting the saga execution. Worse, in the case of sagas calling the volume delete subsaga, subsequent calls will also halt. With the introduction of a physical disk policy, Nexus can know when to stop retrying a call - the destination service is gone, so the known result is an error. This commit adds a `ProgenitorOperationRetry` object that takes an operation to retry plus a "gone" check, and checks each retry iteration if the destination is gone. If it is, then bail out, otherwise assume that any errors seen are transient. Further work is required to deprecate the `retry_until_known_result` function, as retrying indefinitely is a bad pattern. Fixes oxidecomputer#4331 Fixes oxidecomputer#5022
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,159 @@ | ||
| // This Source Code Form is subject to the terms of the Mozilla Public | ||
| // License, v. 2.0. If a copy of the MPL was not distributed with this | ||
| // file, You can obtain one at https://mozilla.org/MPL/2.0/. | ||
|
|
||
| use futures::Future; | ||
| use slog::warn; | ||
| use slog::Logger; | ||
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| use crate::api::external::Error; | ||
| use crate::backoff::retry_notify; | ||
| use crate::backoff::retry_policy_internal_service; | ||
| use crate::backoff::BackoffError; | ||
|
|
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| #[derive(Debug)] | ||
| pub enum ProgenitorOperationRetryError<E> { | ||
| /// Nexus determined that the operation will never return a known result | ||
| /// because the remote server is gone. | ||
| Gone, | ||
|
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| /// Attempting to check if the retry loop should be stopped failed | ||
| GoneCheckError(Error), | ||
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| /// The retry loop progenitor operation saw a permanent client error | ||
| ProgenitorError(progenitor_client::Error<E>), | ||
| } | ||
|
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| /// Retry a progenitor client operation until a known result is returned, or | ||
| /// until something tells us that we should stop trying. | ||
| /// | ||
| /// Saga execution relies on the outcome of an external call being known: since | ||
| /// they are idempotent, reissue the external call until a known result comes | ||
| /// back. Retry if a communication error is seen, or if another retryable error | ||
| /// is seen. | ||
| /// | ||
| /// During the retry loop, call the supplied `gone_check` function to see if the | ||
| /// retry loop should be aborted: in the cases where Nexus can _know_ that a | ||
| /// request will never complete, the retry loop must be aborted. Otherwise, | ||
| /// Nexus will indefinitely retry until some known result is returned. | ||
| /// | ||
| /// Note that retrying is only valid if the `operation` itself is idempotent. | ||
| pub struct ProgenitorOperationRetry< | ||
| T, | ||
| E: std::fmt::Debug, | ||
| F: FnMut() -> Fut, | ||
| Fut: Future<Output = Result<T, progenitor_client::Error<E>>>, | ||
| BF: FnMut() -> BFut, | ||
| BFut: Future<Output = Result<bool, Error>>, | ||
| > { | ||
| operation: F, | ||
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| /// If Nexus knows that the supplied operation will never successfully | ||
| /// complete, then `gone_check` should return true. | ||
| gone_check: BF, | ||
| } | ||
|
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| impl< | ||
| T, | ||
| E: std::fmt::Debug, | ||
| F: FnMut() -> Fut, | ||
| Fut: Future<Output = Result<T, progenitor_client::Error<E>>>, | ||
| BF: FnMut() -> BFut, | ||
| BFut: Future<Output = Result<bool, Error>>, | ||
| > ProgenitorOperationRetry<T, E, F, Fut, BF, BFut> | ||
| { | ||
| pub fn new(operation: F, gone_check: BF) -> Self { | ||
| Self { operation, gone_check } | ||
| } | ||
|
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||
| pub async fn run( | ||
| mut self, | ||
| log: &Logger, | ||
| ) -> Result<T, ProgenitorOperationRetryError<E>> { | ||
| retry_notify( | ||
| retry_policy_internal_service(), | ||
| move || { | ||
| let gone_check = (self.gone_check)(); | ||
| let f = (self.operation)(); | ||
|
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| async move { | ||
| match gone_check.await { | ||
| Ok(dest_is_gone) => { | ||
| if dest_is_gone { | ||
| return Err(BackoffError::Permanent( | ||
| ProgenitorOperationRetryError::Gone | ||
| )); | ||
| } | ||
| } | ||
|
|
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| Err(e) => { | ||
| return Err(BackoffError::Permanent( | ||
| ProgenitorOperationRetryError::GoneCheckError(e) | ||
| )); | ||
| } | ||
| } | ||
|
|
||
| match f.await { | ||
| Err(progenitor_client::Error::CommunicationError(e)) => { | ||
| warn!( | ||
| log, | ||
| "saw transient communication error {}, retrying...", | ||
| e, | ||
| ); | ||
|
|
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| Err(BackoffError::transient( | ||
| ProgenitorOperationRetryError::ProgenitorError( | ||
| progenitor_client::Error::CommunicationError(e) | ||
| ) | ||
| )) | ||
| } | ||
|
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||
| Err(progenitor_client::Error::ErrorResponse( | ||
| response_value, | ||
| )) => { | ||
| match response_value.status() { | ||
| // Retry on 503 or 429 | ||
| http::StatusCode::SERVICE_UNAVAILABLE | ||
| | http::StatusCode::TOO_MANY_REQUESTS => { | ||
| Err(BackoffError::transient( | ||
| ProgenitorOperationRetryError::ProgenitorError( | ||
| progenitor_client::Error::ErrorResponse( | ||
| response_value | ||
| ) | ||
| ) | ||
| )) | ||
| } | ||
|
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| // Anything else is a permanent error | ||
| _ => Err(BackoffError::Permanent( | ||
| ProgenitorOperationRetryError::ProgenitorError( | ||
| progenitor_client::Error::ErrorResponse( | ||
| response_value | ||
| ) | ||
| ) | ||
| )) | ||
| } | ||
| } | ||
|
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| Err(e) => { | ||
| warn!(log, "saw permanent error {}, aborting", e,); | ||
|
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| Err(BackoffError::Permanent( | ||
| ProgenitorOperationRetryError::ProgenitorError(e) | ||
| )) | ||
| } | ||
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| Ok(v) => Ok(v), | ||
| } | ||
| } | ||
| }, | ||
| |error: ProgenitorOperationRetryError<E>, delay| { | ||
| warn!( | ||
| log, | ||
| "failed external call ({:?}), will retry in {:?}", error, delay, | ||
| ); | ||
| }, | ||
| ) | ||
| .await | ||
| } | ||
| } |
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