Function InitFrontend

pkg/frontend/config.go:40–73

InitFrontend initializes frontend (either V1 -- without scheduler, or V2 -- with scheduler) or no frontend at all if downstream Prometheus URL is used instead. Returned RoundTripper can be wrapped in more round-tripper middlewares, and then eventually registered into HTTP server using the Handler f

(cfg CombinedFrontendConfig, limits v1.Limits, grpcListenPort int, log log.Logger, reg prometheus.Registerer, retry *transport.Retry)

// into HTTP server using the Handler from this package. Returned RoundTripper is always non-nil
// (if there are no errors), and it uses the returned frontend (if any).
func InitFrontend(cfg CombinedFrontendConfig, limits v1.Limits, grpcListenPort int, log log.Logger, reg prometheus.Registerer, retry *transport.Retry) (http.RoundTripper, *v1.Frontend, *v2.Frontend, error) {
	switch {
	case cfg.DownstreamURL != "":
		// If the user has specified a downstream Prometheus, then we should use that.
		rt, err := NewDownstreamRoundTripper(cfg.DownstreamURL, http.DefaultTransport)
		return rt, nil, nil, err

	case cfg.FrontendV2.SchedulerAddress != "":
		// If query-scheduler address is configured, use Frontend.
		if cfg.FrontendV2.Addr == "" {
			addr, err := util.GetFirstAddressOf(cfg.FrontendV2.InfNames)
			if err != nil {
				return nil, nil, nil, errors.Wrap(err, "failed to get frontend address")
			}

			cfg.FrontendV2.Addr = addr
		}

		if cfg.FrontendV2.Port == 0 {
			cfg.FrontendV2.Port = grpcListenPort
		}

		fr, err := v2.NewFrontend(cfg.FrontendV2, limits, log, reg, retry)
		return transport.AdaptGrpcRoundTripperToHTTPRoundTripper(fr), nil, fr, err

	default:
		// No scheduler = use original frontend.
		fr, err := v1.New(cfg.FrontendV1, limits, log, reg, retry)
		if err != nil {
			return nil, nil, nil, err
		}
		return transport.AdaptGrpcRoundTripperToHTTPRoundTripper(fr), fr, nil, nil
	}
}