Retries - ReverseProxy.ErrorHandler based approach #61
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nstogner
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pkg/proxy/request.go
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| func (pr *proxyRequest) httpRequest() *http.Request { | ||
| clone := pr.r.Clone(pr.r.Context()) | ||
| clone.Body = io.NopCloser(bytes.NewReader(pr.body)) |
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In the scenario with x-model header set, this behaviour is not correct. The body is empty and the original Reader overwritten.
it may also be worth to optimize for the happy path (without a retry) and lazy fill the buffer (with a TeeReader for example).
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Good catch, I'll look at the TeeReader approach. I think we could also do a nil check on pr.body before resetting close.Body here as well.
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Took the approach of checking for nil
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Also added a test case for making sure the right response body was reaching the backend.
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I think this is fixed now. I included a test case for this.
pkg/proxy/handler_test.go
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| backendCode: http.StatusInternalServerError, | ||
| backendBody: `{"err":"oh no!"}`, | ||
| expCode: http.StatusBadGateway, | ||
| expBody: `{"error":"Bad Gateway"}` + "\n", |
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When retry is enabled, the original backend error msg is never passed to the client. This can be a valid design decision but we should be sensible what error codes are "retryable". Do you have some scenarios for 500 in mind that can succeed on a retry?
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Good catch, we should probably only filter 500s
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Scratch that, I am going to just pipe through the response in the case where it got an http response by filtering out retry errors.
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pkg/proxy/handler.go
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| // This point could be reached if a bad response code was sent by the backend | ||
| // or | ||
| // if there was an issue with the connection and no response was ever received. | ||
| if err != nil && pr.attempt < h.MaxRetries { |
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It would be good to abort early when the request context is canceled. I have debugged retries in #65 that never hit a backend
| if err != nil && pr.attempt < h.MaxRetries { | |
| if err != nil && | |
| r.Context().Err() == nil && | |
| pr.attempt < h.MaxRetries { |
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It looks like there are checks for the context being done in the reverse proxy .ServeHTTP function. Do you know what cases it would fix to also do the check here?
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🤔 the result to the end use may be the same but you get there with fewer steps. Your code would be in charge instead of relying on the stdlib proxy. I stumbled upon this when I was debugging and saw the loop iteration but no backend hit.
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@alpe Added a test case in the handler tests for the failure you mentioned. Seeing it now. |
pkg/proxy/handler.go
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| // This point could be reached if a bad response code was sent by the backend | ||
| // or | ||
| // if there was an issue with the connection and no response was ever received. | ||
| if err != nil && pr.attempt < h.MaxRetries { |
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🤔 the result to the end use may be the same but you get there with fewer steps. Your code would be in charge instead of relying on the stdlib proxy. I stumbled upon this when I was debugging and saw the loop iteration but no backend hit.
Allow for retrying failed requests to backends. Default to 1 retry per lingo-request.
Fixes #48
Builds on work done by @alpe in #64 and #51.