integration: Add TestDaemonDNSFallback

Signed-off-by: Tibor Vass <tibor@docker.com>
(cherry picked from commit e5ad8b14daf0a1ddb12c0b83d153531afffb908b)
Signed-off-by: Tibor Vass <tibor@docker.com>

integration/network/dns_test.go

@@ -0,0 +1,35 @@
+package network // import "github.com/docker/docker/integration/network"
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/integration/internal/container"
+	"github.com/docker/docker/integration/internal/network"
+	"github.com/docker/docker/internal/test/daemon"
+	"gotest.tools/poll"
+	"gotest.tools/skip"
+)
+
+func TestDaemonDNSFallback(t *testing.T) {
+	skip.If(t, testEnv.IsRemoteDaemon, "cannot start daemon on remote test run")
+	skip.If(t, testEnv.DaemonInfo.OSType != "linux")
+	skip.If(t, IsUserNamespace())
+
+	d := daemon.New(t)
+	d.StartWithBusybox(t, "-b", "none", "--dns", "127.127.127.1", "--dns", "8.8.8.8")
+	defer d.Stop(t)
+
+	c := d.NewClientT(t)
+	ctx := context.Background()
+
+	network.CreateNoError(ctx, t, c, "test")
+	defer c.NetworkRemove(ctx, "test")
+
+	cid := container.Run(ctx, t, c, container.WithNetworkMode("test"), container.WithCmd("nslookup", "docker.com"))
+	defer c.ContainerRemove(ctx, cid, types.ContainerRemoveOptions{Force: true})
+
+	poll.WaitOn(t, container.IsSuccessful(ctx, c, cid), poll.WithDelay(100*time.Millisecond), poll.WithTimeout(2*time.Second))
+}