Linked zones: shared records kept in step across views

Zones of the same name in different views can be linked. Shared records
are kept in step: a change in one view reaches the others in the same
changeset, as explicit operations, so the diff, permission checks,
history and undo cover every view. Records local to a view override the
shared records of that name and type there; removing the override brings
the shared ones back, and sharing a view's version makes it every view's.
Each zone keeps its own options, serial and file.

Linking existing zones changes no answer: what is the same everywhere
becomes shared, the rest stays local. Unlinking keeps every record, all
local. ACME challenges are written once per link, and --view all changes
a link once. jarl zone link/unlink, zone create --link-with, record
--local/--shared, LINK column, web UI controls, POST /zones/{zone}/link
and /unlink, validation checks linked_*, store migration 11, docs and
e2e.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/engine/expand.go

@@ -131,7 +131,24 @@ func dateSerial(now time.Time) uint32 {
 }
 
 func (x *expander) expand(req Request) ([]model.Op, error) {
+	ops, err := x.expandOne(req)
+	if err != nil {
+		return nil, err
+	}
 	switch req.Op {
+	case OpRecordCreate, OpRecordUpdate, OpRecordDelete, OpRRSetReplace, OpRecordDisable, OpRecordEnable:
+		// Changes to linked zones reach the other zones of the link.
+		return x.linkSync(ops)
+	}
+	return ops, nil
+}
+
+func (x *expander) expandOne(req Request) ([]model.Op, error) {
+	switch req.Op {
+	case OpZoneLink:
+		return x.zoneLink(req)
+	case OpZoneUnlink:
+		return x.zoneUnlink(req)
 	case OpZoneCreate:
 		return x.zoneCreate(req)
 	case OpZoneUpdate, OpZoneDelete:
@@ -152,7 +169,24 @@ func (x *expander) expand(req Request) ([]model.Op, error) {
 			}
 			return []model.Op{x.versioned(req, z.Version, "enable zone "+zoneDesc(x.st, z))}, nil
 		}
-		return []model.Op{x.versioned(req, z.Version, "zone "+verb+" "+zoneDesc(x.st, z))}, nil
+		ops := []model.Op{x.versioned(req, z.Version, "zone "+verb+" "+zoneDesc(x.st, z))}
+		if req.Op == OpZoneDelete {
+			if rest := x.st.LinkedWith(z); len(rest) == 1 {
+				ops = append(ops, x.unlinkOps(rest[0], "unlink zone "+zoneDesc(x.st, rest[0])+": the zone it was linked with is deleted")...)
+			}
+		} else {
+			var in ZoneInput
+			if err := decode(req.Data, &in); err != nil {
+				return nil, err
+			}
+			if in.LinkGroup != nil && *in.LinkGroup != z.LinkGroup {
+				return nil, errf(KindBadRequest, "link zones with zone.link and zone.unlink (jarl zone link / unlink)")
+			}
+			if in.LinkWith != "" {
+				return nil, errf(KindBadRequest, "link_with is for new zones; link existing ones with zone.link (jarl zone link)")
+			}
+		}
+		return ops, nil
 	case OpRecordCreate:
 		return x.recordCreate(req)
 	case OpRecordUpdate:
@@ -355,7 +389,25 @@ func (x *expander) zoneCreate(req Request) ([]model.Op, error) {
 	records := in.Records
 	cloneFrom := in.CloneFrom
 	zoneOpts := in.Options
-	in.Nameservers, in.Records, in.CloneFrom, in.Options = nil, nil, 0, nil
+	linkWith := in.LinkWith
+	in.Nameservers, in.Records, in.CloneFrom, in.Options, in.LinkWith, in.LinkGroup = nil, nil, 0, nil, "", nil
+	if linkWith != "" {
+		if cloneFrom != 0 {
+			return nil, errf(KindBadRequest, "give clone_from or link_with, not both")
+		}
+		v := x.st.ViewByName(linkWith)
+		if v == nil {
+			return nil, errf(KindNotFound, "view %q does not exist", linkWith)
+		}
+		o := x.st.FindZone(name, v.ID)
+		if o == nil {
+			return nil, errf(KindNotFound, "view %s has no zone %s to link with", v.Name, dnsname.Display(name))
+		}
+		if o.Type != model.ZonePrimary || zt != model.ZonePrimary {
+			return nil, errf(KindBadRequest, "only primary zones can be linked")
+		}
+		cloneFrom = o.ID
+	}
 
 	set := x.st.Settings
 	var src *model.Zone
@@ -480,9 +532,30 @@ func (x *expander) zoneCreate(req Request) ([]model.Op, error) {
 			return nil, err
 		}
 	}
+	var linkOps []model.Op
+	if src != nil && linkWith != "" {
+		// The new zone joins src's link, or starts one with src: then
+		// all of src's records become shared.
+		group := src.LinkGroup
+		if group == 0 {
+			group = src.ID
+			linkOps = x.shareAllOps(src, group)
+		}
+		in.LinkGroup = &group
+	}
 	if src != nil {
 		for _, r := range x.st.ZoneRecords(src.ID) {
+			if linkWith != "" && src.LinkGroup != 0 && r.SharedID == 0 {
+				continue // local to src's view
+			}
 			ri := RecordInput{Name: model.Ptr(r.Name), Type: model.Ptr(r.Type), Data: model.Ptr(r.Data), Comment: model.Ptr(r.Comment)}
+			if linkWith != "" {
+				id := r.SharedID
+				if id == 0 {
+					id = r.ID
+				}
+				ri.SharedID = &id
+			}
 			if r.Disabled {
 				ri.Disabled = model.Ptr(true)
 			}
@@ -512,10 +585,12 @@ func (x *expander) zoneCreate(req Request) ([]model.Op, error) {
 			summary += " in view " + v.Name
 		}
 	}
-	if src != nil {
+	if src != nil && linkWith != "" {
+		summary += " (linked with " + zoneDesc(x.st, src) + ")"
+	} else if src != nil {
 		summary += " (copy of " + zoneDesc(x.st, src) + ")"
 	}
-	ops := []model.Op{newOp(OpZoneCreate, ids[0], 0, in, summary)}
+	ops := append(linkOps, newOp(OpZoneCreate, ids[0], 0, in, summary))
 	for i, zo := range zoneOpts {
 		oi := OptionInput{Scope: model.Ptr(model.ScopeZone), ScopeID: model.Ptr(ids[0]), Name: model.Ptr(zo.Name), Value: model.Ptr(zo.Value)}
 		if zo.Comment != "" {
@@ -666,7 +741,27 @@ func (x *expander) recordCreate(req Request) ([]model.Op, error) {
 	if err != nil {
 		return nil, err
 	}
-	ops := []model.Op{newOp(OpRecordCreate, ids[0], 0, in, fmt.Sprintf("add %s%s IN %s %s", owner, ttlText(in.TTL), p.Type, p.Data))}
+	summary := fmt.Sprintf("add %s%s IN %s %s", owner, ttlText(in.TTL), p.Type, p.Data)
+	in.SharedID = nil
+	if z.LinkGroup != 0 {
+		local, err := x.localFor(z, owner, p.Type, in.Local)
+		if err != nil {
+			return nil, err
+		}
+		if local {
+			in.SharedID = model.Ptr(int64(0))
+			summary += " (local to view " + x.st.ViewName(z) + ")"
+		} else {
+			if x.st.HasLocal(z.ID, owner, p.Type) {
+				return nil, errf(KindConflict, "%s %s is local in view %s; share the set first (jarl record update ID --shared) or add this one as local", dnsname.Display(owner), p.Type, x.st.ViewName(z))
+			}
+			in.SharedID = &ids[0]
+		}
+	} else if in.Local != nil && *in.Local {
+		return nil, errf(KindBadRequest, "zone %s isn't linked with other views, so its records are local anyway", zoneDesc(x.st, z))
+	}
+	in.Local = nil
+	ops := []model.Op{newOp(OpRecordCreate, ids[0], 0, in, summary)}
 	if ptr {
 		more, err := x.ptrCreate(z, owner, p)
 		if err != nil {
@@ -690,6 +785,35 @@ func (x *expander) recordUpdate(req Request) ([]model.Op, error) {
 	ptr := in.PTR
 	in.PTR = false
 	in.Zone, in.View = "", ""
+	if in.SharedID != nil {
+		return nil, errf(KindBadRequest, "shared_id is managed by Jarl; use local: true or false to make a record local to its view or shared")
+	}
+	var pre []model.Op
+	if in.Local != nil {
+		if z.LinkGroup == 0 {
+			return nil, errf(KindBadRequest, "zone %s isn't linked with other views, so its records are local anyway", zoneDesc(x.st, z))
+		}
+		if want := *in.Local; want != (r.SharedID == 0) {
+			// The whole set of this name and type changes sides.
+			for _, o := range x.st.RRset(z.ID, r.Name, r.Type) {
+				id := int64(0)
+				what := fmt.Sprintf("make %s %s local to view %s", o.Name, o.Type, x.st.ViewName(z))
+				if !want {
+					id = o.ID
+					what = fmt.Sprintf("share %s %s %s with the linked views", o.Name, o.Type, o.Data)
+				}
+				pre = append(pre, newOp(OpRecordUpdate, o.ID, o.Version, RecordInput{SharedID: model.Ptr(id)}, what))
+			}
+			if !want {
+				// Sharing a version makes it every view's.
+				pre = append(pre, x.dropOverrides(z, r.Name, r.Type)...)
+			}
+		}
+		in.Local = nil
+		if string(mustJSON(in)) == "{}" {
+			return pre, nil
+		}
+	}
 	name, typ, data := r.Name, r.Type, r.Data
 	if in.Name != nil {
 		name = *in.Name
@@ -751,11 +875,17 @@ func (x *expander) recordUpdate(req Request) ([]model.Op, error) {
 	case len(changes) > 0:
 		summary += ": " + strings.Join(changes, ", ")
 	}
+	if z.LinkGroup != 0 && r.SharedID != 0 && len(pre) == 0 && (owner != r.Name || p.Type != r.Type) && x.st.HasLocal(z.ID, owner, p.Type) {
+		return nil, errf(KindConflict, "%s %s is local in view %s, so a shared record can't move there", dnsname.Display(owner), p.Type, x.st.ViewName(z))
+	}
 	base := req.BaseVersion
 	if base == 0 {
 		base = r.Version
 	}
-	ops := []model.Op{newOp(OpRecordUpdate, r.ID, base, in, summary)}
+	if len(pre) > 0 {
+		base = 0 // the record was just updated by pre
+	}
+	ops := append(pre, newOp(OpRecordUpdate, r.ID, base, in, summary))
 	disabled := r.Disabled
 	if in.Disabled != nil {
 		disabled = *in.Disabled
@@ -953,17 +1083,35 @@ func (x *expander) rrsetReplace(req Request) ([]model.Op, error) {
 		canon = append(canon, p.Data)
 	}
 	in.ZoneID, in.Zone, in.View, in.Name, in.Type, in.Data = z.ID, "", "", owner, typ, canon
+	where := ""
+	var pre []model.Op
+	if z.LinkGroup != 0 {
+		local, err := x.localFor(z, owner, typ, in.Local)
+		if err != nil {
+			return nil, err
+		}
+		in.Shared = model.Ptr(!local)
+		if local {
+			where = " (local to view " + x.st.ViewName(z) + ")"
+		} else if in.Local != nil {
+			// Explicitly shared: this version becomes every view's.
+			pre = x.dropOverrides(z, owner, typ)
+		}
+	} else if in.Local != nil && *in.Local {
+		return nil, errf(KindBadRequest, "zone %s isn't linked with other views, so its records are local anyway", zoneDesc(x.st, z))
+	}
+	in.Local = nil
 	if len(canon) > 0 {
 		in.NewIDs, err = x.ids(len(canon))
 		if err != nil {
 			return nil, err
 		}
 	}
-	summary := fmt.Sprintf("set %s%s IN %s to [%s]", owner, ttlText(in.TTL), typ, strings.Join(canon, ", "))
+	summary := fmt.Sprintf("set %s%s IN %s to [%s]%s", owner, ttlText(in.TTL), typ, strings.Join(canon, ", "), where)
 	if len(canon) == 0 {
-		summary = fmt.Sprintf("delete all %s records of %s", typ, owner)
+		summary = fmt.Sprintf("delete all %s records of %s%s", typ, owner, where)
 	}
-	return []model.Op{newOp(OpRRSetReplace, 0, 0, in, summary)}, nil
+	return append(pre, newOp(OpRRSetReplace, 0, 0, in, summary)), nil
 }
 
 func (x *expander) viewCreate(req Request) ([]model.Op, error) {