fix(server): cannot update placement group (#902)

The `placement_group` field name must be `placement_group_id`, the
placement group could not be updated while using the wrong field name.

When no placement group is set, we find an id of `0`, which *seem* to be
expected by Terraform.

internal/server/resource.go

@@ -659,8 +659,8 @@ func resourceServerUpdate(ctx context.Context, d *schema.ResourceData, m interfa
 		}
 	}
 
-	if d.HasChange("placement_group") {
-		placementGroupID := d.Get("placement_group").(int)
+	if d.HasChange("placement_group_id") {
+		placementGroupID := d.Get("placement_group_id").(int)
 		if err := setPlacementGroup(ctx, c, server, placementGroupID); err != nil {
 			return hcloudutil.ErrorToDiag(err)
 		}
@@ -1212,6 +1212,8 @@ func getServerAttributes(d *schema.ResourceData, s *hcloud.Server) map[string]in
 
 	if s.PlacementGroup != nil {
 		res["placement_group_id"] = s.PlacementGroup.ID
+	} else {
+		res["placement_group_id"] = nil
 	}
 
 	return res
@@ -1249,6 +1251,14 @@ func getPlacementGroup(ctx context.Context, c *hcloud.Client, id int) (*hcloud.P
 
 func setPlacementGroup(ctx context.Context, c *hcloud.Client, server *hcloud.Server, id int) error {
 	if server.PlacementGroup != nil {
+		if server.Status != hcloud.ServerStatusOff {
+			// Removing PG requires the server to be shut down before, this is an invasive operation. We do not currently
+			// warn the user about this, so we prefer to forbid the operation until we have a proper framework for
+			// shutting down + warning in place.
+			return fmt.Errorf("removing a running server from a placement group is currently not supported in the provider. " +
+				"You can shutdown the server yourself, apply the changes again and then start the server manually as a workaround")
+		}
+
 		action, _, err := c.Server.RemoveFromPlacementGroup(ctx, server)
 		if err != nil {
 			return err

internal/server/resource_test.go

@@ -1,6 +1,7 @@
 package server_test
 
 import (
+	"context"
 	"crypto/sha1"
 	"encoding/base64"
 	"fmt"
@@ -22,6 +23,7 @@ import (
 	"github.com/hetznercloud/terraform-provider-hcloud/internal/teste2e"
 	"github.com/hetznercloud/terraform-provider-hcloud/internal/testsupport"
 	"github.com/hetznercloud/terraform-provider-hcloud/internal/testtemplate"
+	"github.com/hetznercloud/terraform-provider-hcloud/internal/util/hcloudutil"
 )
 
 func TestServerResource_Basic(t *testing.T) {
@@ -898,6 +900,13 @@ func TestServerResource_PlacementGroup(t *testing.T) {
 	}
 	srvRes.SetRName("server-placement-group")
 
+	srvResNoPG := &server.RData{
+		Name:  srvRes.Name,
+		Type:  srvRes.Type,
+		Image: srvRes.Image,
+	}
+	srvResNoPG.SetRName("server-placement-group")
+
 	tmplMan := testtemplate.Manager{}
 
 	resource.ParallelTest(t, resource.TestCase{
@@ -915,15 +924,65 @@ func TestServerResource_PlacementGroup(t *testing.T) {
 				Check: resource.ComposeTestCheckFunc(
 					testsupport.CheckResourceExists(srvRes.TFID(), server.ByID(t, &srv)),
 					testsupport.CheckResourceExists(pgRes.TFID(), placementgroup.ByID(t, &pg)),
-					resource.TestCheckResourceAttr(srvRes.TFID(), "name",
-						fmt.Sprintf("server-placement-group--%d", tmplMan.RandInt)),
+					resource.TestCheckResourceAttr(srvRes.TFID(), "name", fmt.Sprintf("server-placement-group--%d", tmplMan.RandInt)),
 					resource.TestCheckResourceAttr(srvRes.TFID(), "server_type", srvRes.Type),
 					resource.TestCheckResourceAttr(srvRes.TFID(), "image", srvRes.Image),
 					testsupport.CheckResourceAttrFunc(srvRes.TFID(), "placement_group_id", func() string {
 						return strconv.Itoa(pg.ID)
 					}),
 				),
 			},
+			{
+				// Try to remove PG of running server -> error
+				Config: tmplMan.Render(t,
+					"testdata/r/hcloud_placement_group", pgRes,
+					"testdata/r/hcloud_server", srvResNoPG,
+				),
+				ExpectError: regexp.MustCompile("removing a running server from a placement group is currently not supported in the provider.*"),
+			},
+			{
+				// Remove Placement Group
+				PreConfig: func() {
+					ctx := context.TODO()
+					// Removing PG is not support only in TF, we need to shut down the server manually beforehand
+					client, err := testsupport.CreateClient()
+					if err != nil {
+						t.Errorf("PreConfig: failed to create client: %v", err)
+						return
+					}
+					action, _, err := client.Server.Poweroff(ctx, &srv)
+					if err != nil {
+						t.Errorf("PreConfig: failed to power off server: %v", err)
+						return
+					}
+					err = hcloudutil.WaitForAction(ctx, &client.Action, action)
+					if err != nil {
+						t.Errorf("PreConfig: power off server action failed: %v", err)
+						return
+					}
+				},
+				Config: tmplMan.Render(t,
+					"testdata/r/hcloud_placement_group", pgRes,
+					"testdata/r/hcloud_server", srvResNoPG,
+				),
+				Check: resource.ComposeTestCheckFunc(
+					resource.TestCheckResourceAttr(srvResNoPG.TFID(), "status", "off"),
+					resource.TestCheckResourceAttr(srvResNoPG.TFID(), "placement_group_id", "0"),
+				),
+			},
+			{
+				// Add Placement Group back
+				Config: tmplMan.Render(t,
+					"testdata/r/hcloud_placement_group", pgRes,
+					"testdata/r/hcloud_server", srvRes,
+				),
+				Check: resource.ComposeTestCheckFunc(
+					resource.TestCheckResourceAttr(srvResNoPG.TFID(), "status", "running"),
+					testsupport.CheckResourceAttrFunc(srvRes.TFID(), "placement_group_id", func() string {
+						return strconv.Itoa(pg.ID)
+					}),
+				),
+			},
 		},
 	})
 }