traefik/pkg/middlewares/emptybackendhandler/empty_backend_handler.go

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package emptybackendhandler
import (
"net/http"
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"github.com/containous/traefik/v2/pkg/healthcheck"
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)
// EmptyBackend is a middleware that checks whether the current Backend
// has at least one active Server in respect to the healthchecks and if this
// is not the case, it will stop the middleware chain and respond with 503.
type emptyBackend struct {
next healthcheck.BalancerHandler
}
// New creates a new EmptyBackend middleware.
func New(lb healthcheck.BalancerHandler) http.Handler {
return &emptyBackend{next: lb}
}
// ServeHTTP responds with 503 when there is no active Server and otherwise
// invokes the next handler in the middleware chain.
func (e *emptyBackend) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
if len(e.next.Servers()) == 0 {
rw.WriteHeader(http.StatusServiceUnavailable)
_, err := rw.Write([]byte(http.StatusText(http.StatusServiceUnavailable)))
if err != nil {
http.Error(rw, err.Error(), http.StatusInternalServerError)
}
} else {
e.next.ServeHTTP(rw, req)
}
}