[shim] Fix DCGMWrapperInterface nil check (bis) (#3001)

Fixes: #2997

Author: un-def

runner/internal/shim/api/handlers.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"errors"
 	"net/http"
-	"reflect"
 
 	"github.com/dstackai/dstack/runner/internal/api"
 	"github.com/dstackai/dstack/runner/internal/log"
@@ -25,7 +24,7 @@ func (s *ShimServer) HealthcheckHandler(w http.ResponseWriter, r *http.Request)
 func (s *ShimServer) InstanceHealthHandler(w http.ResponseWriter, r *http.Request) (interface{}, error) {
 	ctx := r.Context()
 	response := InstanceHealthResponse{}
-	if !reflect.ValueOf(s.dcgmWrapper).IsNil() {
+	if s.dcgmWrapper != nil {
 		if dcgmHealth, err := s.dcgmWrapper.GetHealth(); err != nil {
 			log.Error(ctx, "failed to get health from DCGM", "err", err)
 		} else {

runner/internal/shim/api/server.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"net"
 	"net/http"
+	"reflect"
 	"sync"
 
 	"github.com/dstackai/dstack/runner/internal/api"
@@ -29,7 +30,7 @@ type ShimServer struct {
 	runner TaskRunner
 
 	dcgmExporter *dcgm.DCGMExporter
-	dcgmWrapper  dcgm.DCGMWrapperInterface
+	dcgmWrapper  dcgm.DCGMWrapperInterface // interface with nil value normalized to plain nil
 
 	version string
 }
@@ -38,6 +39,9 @@ func NewShimServer(
 	ctx context.Context, address string, version string,
 	runner TaskRunner, dcgmExporter *dcgm.DCGMExporter, dcgmWrapper dcgm.DCGMWrapperInterface,
 ) *ShimServer {
+	if dcgmWrapper != nil && reflect.ValueOf(dcgmWrapper).IsNil() {
+		dcgmWrapper = nil
+	}
 	r := api.NewRouter()
 	s := &ShimServer{
 		HttpServer: &http.Server{