feat(dns): allow setting an externally managed cluster domain (uc dns set)

* feat: add uc dns set

This allows manual setting of the cluster's domain name. I use this to
make the local cluster admin aware that this has been done.
(and then manually update the external dns)

```
% uc dns set ctrl.u.science.ru.nl
Set cluster domain: ctrl.u.science.ru.nl
Deploy the Caddy reverse proxy service ('uc caddy deploy') to enable internet access to your services via the reserved or your custom domain.

% uc dns show
ctrl.u.science.ru.nl

% uc dns set ctrl.u.science.ru.nl
Error: domain already reserved

% uc dns release
Released cluster domain: ctrl.u.science.ru.nl
```

See: #37

Signed-off-by: Miek Gieben <miek@miek.nl>

* docs

Signed-off-by: Miek Gieben <miek@miek.nl>

* check validatity

Signed-off-by: Miek Gieben <miek@miek.nl>

* No need to call out to update anything, as set doesnt use uncloud dns

Signed-off-by: Miek Gieben <miek@miek.nl>

* Ignore domain when there is no endpoint

Prevents this error, when you know what you're doing:

    Error: failed to update DNS records pointing to caddy service: create cluster domain records in Uncloud DNS: rpc error: code = Unknown desc = Post "/domains/ctrl.u.science.ru.nl/records": unsupported protocol scheme ""

Signed-off-by: Miek Gieben <miek@miek.nl>

* from main

Signed-off-by: Miek Gieben <miek@miek.nl>

* mise proto && make cli-docs

Signed-off-by: Miek Gieben <miek@miek.nl>

* Rebase and and generate protos again

Signed-off-by: Miek Gieben <miek@miek.nl>

* Rebase and fix

Signed-off-by: Miek Gieben <miek@miek.nl>

* feat(dns): allow setting an externally managed cluster domain

---------

Signed-off-by: Miek Gieben <miek@miek.nl>
Co-authored-by: Pasha Sviderski <me@psviderski.name>

internal/machine/cluster/dns.go

@@ -4,20 +4,24 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"strings"
 
+	"github.com/miekg/dns"
 	"github.com/psviderski/uncloud/api/pb"
-	"github.com/psviderski/uncloud/internal/dns"
+	undns "github.com/psviderski/uncloud/internal/dns"
 	"github.com/psviderski/uncloud/internal/machine/store"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/emptypb"
 )
 
-// uncloudDNSKey is the key used to store the details of the reserved domain in the store.
+// uncloudDNSKey stores the cluster domain and, when reserved, its Uncloud DNS credentials.
 const uncloudDNSKey = "uncloud_dns"
 
 type uncloudDNSDomain struct {
 	// Endpoint is the API endpoint of the Uncloud DNS service where the domain is reserved.
+	// An empty endpoint means the domain is managed externally.
 	Endpoint string
 	Name     string
 	// TODO: encrypt the token in the store.
@@ -34,14 +38,14 @@ func (c *Cluster) ReserveDomain(ctx context.Context, req *pb.ReserveDomainReques
 	}
 
 	if _, err := c.storedDomain(ctx); err == nil {
-		return nil, status.Errorf(codes.AlreadyExists, "domain already reserved")
+		return nil, status.Error(codes.AlreadyExists, "cluster domain already configured")
 	} else {
 		if s := status.Convert(err); s.Code() != codes.NotFound {
 			return nil, err
 		}
 	}
 
-	dnsClient := dns.NewClient()
+	dnsClient := undns.NewClient()
 	name, token, err := dnsClient.ReserveDomain(req.Endpoint)
 	if err != nil {
 		return nil, status.Error(codes.Internal, err.Error())
@@ -60,7 +64,7 @@ func (c *Cluster) ReserveDomain(ctx context.Context, req *pb.ReserveDomainReques
 		return nil, status.Errorf(codes.Internal, "store reserved domain: %v", err)
 	}
 
-	return &pb.Domain{Name: name}, nil
+	return &pb.Domain{Name: name, Reserved: proto.Bool(true)}, nil
 }
 
 func (c *Cluster) GetDomain(ctx context.Context, _ *emptypb.Empty) (*pb.Domain, error) {
@@ -73,7 +77,7 @@ func (c *Cluster) GetDomain(ctx context.Context, _ *emptypb.Empty) (*pb.Domain,
 		return nil, err
 	}
 
-	return &pb.Domain{Name: domain.Name}, nil
+	return &pb.Domain{Name: domain.Name, Reserved: proto.Bool(domain.Endpoint != "")}, nil
 }
 
 func (c *Cluster) storedDomain(ctx context.Context) (uncloudDNSDomain, error) {
@@ -103,13 +107,63 @@ func (c *Cluster) ReleaseDomain(ctx context.Context, _ *emptypb.Empty) (*pb.Doma
 	if err != nil {
 		return nil, err
 	}
+	if domain.Endpoint == "" {
+		return nil, status.Error(codes.FailedPrecondition,
+			"cluster domain is set manually, use 'uc dns set \"\"' to unset it")
+	}
 
 	if err = c.store.Delete(ctx, uncloudDNSKey); err != nil {
 		return nil, status.Errorf(codes.Internal, "delete domain from store: %v", err)
 	}
 	// TODO: implement and call Uncloud DNS endpoint to release/delete the domain.
 
-	return &pb.Domain{Name: domain.Name}, nil
+	return &pb.Domain{Name: domain.Name, Reserved: proto.Bool(true)}, nil
+}
+
+func (c *Cluster) SetDomain(ctx context.Context, req *pb.SetDomainRequest) (*emptypb.Empty, error) {
+	if err := c.checkReady(); err != nil {
+		return nil, err
+	}
+
+	name := req.GetName()
+	if name != "" {
+		if labels, ok := dns.IsDomainName(name); !ok || labels < 2 {
+			return nil, status.Errorf(codes.InvalidArgument,
+				"invalid cluster domain '%s': must be a valid domain name with at least two labels", name)
+		}
+	}
+	name = strings.ToLower(strings.TrimSuffix(name, "."))
+
+	existing, err := c.storedDomain(ctx)
+	if err != nil && status.Code(err) != codes.NotFound {
+		return nil, err
+	}
+	if name == "" {
+		if err == nil {
+			if existing.Endpoint != "" {
+				return nil, status.Error(codes.FailedPrecondition,
+					"cluster domain is reserved in Uncloud DNS, use 'uc dns release' to release it")
+			}
+			if err := c.store.Delete(ctx, uncloudDNSKey); err != nil {
+				return nil, status.Errorf(codes.Internal, "unset cluster domain: %v", err)
+			}
+		}
+		return &emptypb.Empty{}, nil
+	}
+	if err == nil {
+		return nil, status.Error(codes.AlreadyExists, "cluster domain already configured")
+	}
+
+	domain := uncloudDNSDomain{Name: name}
+	domainJSON, err := json.Marshal(domain)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "marshal set domain for store: %v", err)
+	}
+	if err = c.store.Put(ctx, uncloudDNSKey, domainJSON); err != nil {
+		return nil, status.Errorf(codes.Internal, "store set domain: %v", err)
+	}
+
+	return &emptypb.Empty{}, nil
 }
 
 func (c *Cluster) CreateDomainRecords(
@@ -124,12 +178,16 @@ func (c *Cluster) CreateDomainRecords(
 		return nil, err
 	}
 
-	dnsClient := dns.NewClient()
-	recordsReq := make([]dns.RecordRequest, len(req.Records))
+	if domain.Endpoint == "" {
+		return nil, status.Error(codes.FailedPrecondition, "cluster domain is not reserved in Uncloud DNS")
+	}
+
+	dnsClient := undns.NewClient()
+	recordsReq := make([]undns.RecordRequest, len(req.Records))
 	for i, r := range req.Records {
-		recordsReq[i] = dns.RecordRequest{
+		recordsReq[i] = undns.RecordRequest{
 			Name:   r.Name,
-			Type:   dns.RecordType(r.Type.String()),
+			Type:   undns.RecordType(r.Type.String()),
 			Values: r.Values,
 		}
 	}
@@ -149,9 +207,9 @@ func (c *Cluster) CreateDomainRecords(
 		}
 
 		switch r.Type {
-		case dns.RecordTypeA:
+		case undns.RecordTypeA:
 			resp.Records[i].Type = pb.DNSRecord_A
-		case dns.RecordTypeAAAA:
+		case undns.RecordTypeAAAA:
 			resp.Records[i].Type = pb.DNSRecord_AAAA
 		}
 	}