traefik/middlewares/empty_backend_handler.go

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package middlewares
import (
"net/http"
"github.com/containous/traefik/healthcheck"
)
// EmptyBackendHandler is a middlware 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 EmptyBackendHandler struct {
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next healthcheck.BalancerHandler
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}
// NewEmptyBackendHandler creates a new EmptyBackendHandler instance.
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func NewEmptyBackendHandler(lb healthcheck.BalancerHandler) *EmptyBackendHandler {
return &EmptyBackendHandler{next: lb}
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}
// ServeHTTP responds with 503 when there is no active Server and otherwise
// invokes the next handler in the middleware chain.
func (h *EmptyBackendHandler) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
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if len(h.next.Servers()) == 0 {
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rw.WriteHeader(http.StatusServiceUnavailable)
rw.Write([]byte(http.StatusText(http.StatusServiceUnavailable)))
} else {
h.next.ServeHTTP(rw, r)
}
}