diff --git a/api/services/control/control.pb.go b/api/services/control/control.pb.go
index b742b005..2c1dc381 100644
--- a/api/services/control/control.pb.go
+++ b/api/services/control/control.pb.go
@@ -1,6 +1,5 @@
-// Code generated by protoc-gen-gogo.
+// Code generated by protoc-gen-gogo. DO NOT EDIT.
 // source: control.proto
-// DO NOT EDIT!
 
 /*
 	Package moby_buildkit_v1 is a generated protocol buffer package.
@@ -21,6 +20,9 @@
 		VertexStatus
 		VertexLog
 		BytesMessage
+		ListWorkersRequest
+		ListWorkersResponse
+		WorkerRecord
 */
 package moby_buildkit_v1
 
@@ -492,6 +494,62 @@ func (m *BytesMessage) GetData() []byte {
 	return nil
 }
 
+type ListWorkersRequest struct {
+	Filter []string `protobuf:"bytes,1,rep,name=filter" json:"filter,omitempty"`
+}
+
+func (m *ListWorkersRequest) Reset()                    { *m = ListWorkersRequest{} }
+func (m *ListWorkersRequest) String() string            { return proto.CompactTextString(m) }
+func (*ListWorkersRequest) ProtoMessage()               {}
+func (*ListWorkersRequest) Descriptor() ([]byte, []int) { return fileDescriptorControl, []int{12} }
+
+func (m *ListWorkersRequest) GetFilter() []string {
+	if m != nil {
+		return m.Filter
+	}
+	return nil
+}
+
+type ListWorkersResponse struct {
+	Record []*WorkerRecord `protobuf:"bytes,1,rep,name=record" json:"record,omitempty"`
+}
+
+func (m *ListWorkersResponse) Reset()                    { *m = ListWorkersResponse{} }
+func (m *ListWorkersResponse) String() string            { return proto.CompactTextString(m) }
+func (*ListWorkersResponse) ProtoMessage()               {}
+func (*ListWorkersResponse) Descriptor() ([]byte, []int) { return fileDescriptorControl, []int{13} }
+
+func (m *ListWorkersResponse) GetRecord() []*WorkerRecord {
+	if m != nil {
+		return m.Record
+	}
+	return nil
+}
+
+type WorkerRecord struct {
+	ID     string            `protobuf:"bytes,1,opt,name=ID,proto3" json:"ID,omitempty"`
+	Labels map[string]string `protobuf:"bytes,2,rep,name=Labels" json:"Labels,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
+}
+
+func (m *WorkerRecord) Reset()                    { *m = WorkerRecord{} }
+func (m *WorkerRecord) String() string            { return proto.CompactTextString(m) }
+func (*WorkerRecord) ProtoMessage()               {}
+func (*WorkerRecord) Descriptor() ([]byte, []int) { return fileDescriptorControl, []int{14} }
+
+func (m *WorkerRecord) GetID() string {
+	if m != nil {
+		return m.ID
+	}
+	return ""
+}
+
+func (m *WorkerRecord) GetLabels() map[string]string {
+	if m != nil {
+		return m.Labels
+	}
+	return nil
+}
+
 func init() {
 	proto.RegisterType((*DiskUsageRequest)(nil), "moby.buildkit.v1.DiskUsageRequest")
 	proto.RegisterType((*DiskUsageResponse)(nil), "moby.buildkit.v1.DiskUsageResponse")
@@ -505,6 +563,9 @@ func init() {
 	proto.RegisterType((*VertexStatus)(nil), "moby.buildkit.v1.VertexStatus")
 	proto.RegisterType((*VertexLog)(nil), "moby.buildkit.v1.VertexLog")
 	proto.RegisterType((*BytesMessage)(nil), "moby.buildkit.v1.BytesMessage")
+	proto.RegisterType((*ListWorkersRequest)(nil), "moby.buildkit.v1.ListWorkersRequest")
+	proto.RegisterType((*ListWorkersResponse)(nil), "moby.buildkit.v1.ListWorkersResponse")
+	proto.RegisterType((*WorkerRecord)(nil), "moby.buildkit.v1.WorkerRecord")
 }
 
 // Reference imports to suppress errors if they are not otherwise used.
@@ -522,6 +583,7 @@ type ControlClient interface {
 	Solve(ctx context.Context, in *SolveRequest, opts ...grpc.CallOption) (*SolveResponse, error)
 	Status(ctx context.Context, in *StatusRequest, opts ...grpc.CallOption) (Control_StatusClient, error)
 	Session(ctx context.Context, opts ...grpc.CallOption) (Control_SessionClient, error)
+	ListWorkers(ctx context.Context, in *ListWorkersRequest, opts ...grpc.CallOption) (*ListWorkersResponse, error)
 }
 
 type controlClient struct {
@@ -613,6 +675,15 @@ func (x *controlSessionClient) Recv() (*BytesMessage, error) {
 	return m, nil
 }
 
+func (c *controlClient) ListWorkers(ctx context.Context, in *ListWorkersRequest, opts ...grpc.CallOption) (*ListWorkersResponse, error) {
+	out := new(ListWorkersResponse)
+	err := grpc.Invoke(ctx, "/moby.buildkit.v1.Control/ListWorkers", in, out, c.cc, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
 // Server API for Control service
 
 type ControlServer interface {
@@ -620,6 +691,7 @@ type ControlServer interface {
 	Solve(context.Context, *SolveRequest) (*SolveResponse, error)
 	Status(*StatusRequest, Control_StatusServer) error
 	Session(Control_SessionServer) error
+	ListWorkers(context.Context, *ListWorkersRequest) (*ListWorkersResponse, error)
 }
 
 func RegisterControlServer(s *grpc.Server, srv ControlServer) {
@@ -709,6 +781,24 @@ func (x *controlSessionServer) Recv() (*BytesMessage, error) {
 	return m, nil
 }
 
+func _Control_ListWorkers_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(ListWorkersRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(ControlServer).ListWorkers(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/moby.buildkit.v1.Control/ListWorkers",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(ControlServer).ListWorkers(ctx, req.(*ListWorkersRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
 var _Control_serviceDesc = grpc.ServiceDesc{
 	ServiceName: "moby.buildkit.v1.Control",
 	HandlerType: (*ControlServer)(nil),
@@ -721,6 +811,10 @@ var _Control_serviceDesc = grpc.ServiceDesc{
 			MethodName: "Solve",
 			Handler:    _Control_Solve_Handler,
 		},
+		{
+			MethodName: "ListWorkers",
+			Handler:    _Control_ListWorkers_Handler,
+		},
 	},
 	Streams: []grpc.StreamDesc{
 		{
@@ -1330,6 +1424,110 @@ func (m *BytesMessage) MarshalTo(dAtA []byte) (int, error) {
 	return i, nil
 }
 
+func (m *ListWorkersRequest) Marshal() (dAtA []byte, err error) {
+	size := m.Size()
+	dAtA = make([]byte, size)
+	n, err := m.MarshalTo(dAtA)
+	if err != nil {
+		return nil, err
+	}
+	return dAtA[:n], nil
+}
+
+func (m *ListWorkersRequest) MarshalTo(dAtA []byte) (int, error) {
+	var i int
+	_ = i
+	var l int
+	_ = l
+	if len(m.Filter) > 0 {
+		for _, s := range m.Filter {
+			dAtA[i] = 0xa
+			i++
+			l = len(s)
+			for l >= 1<<7 {
+				dAtA[i] = uint8(uint64(l)&0x7f | 0x80)
+				l >>= 7
+				i++
+			}
+			dAtA[i] = uint8(l)
+			i++
+			i += copy(dAtA[i:], s)
+		}
+	}
+	return i, nil
+}
+
+func (m *ListWorkersResponse) Marshal() (dAtA []byte, err error) {
+	size := m.Size()
+	dAtA = make([]byte, size)
+	n, err := m.MarshalTo(dAtA)
+	if err != nil {
+		return nil, err
+	}
+	return dAtA[:n], nil
+}
+
+func (m *ListWorkersResponse) MarshalTo(dAtA []byte) (int, error) {
+	var i int
+	_ = i
+	var l int
+	_ = l
+	if len(m.Record) > 0 {
+		for _, msg := range m.Record {
+			dAtA[i] = 0xa
+			i++
+			i = encodeVarintControl(dAtA, i, uint64(msg.Size()))
+			n, err := msg.MarshalTo(dAtA[i:])
+			if err != nil {
+				return 0, err
+			}
+			i += n
+		}
+	}
+	return i, nil
+}
+
+func (m *WorkerRecord) Marshal() (dAtA []byte, err error) {
+	size := m.Size()
+	dAtA = make([]byte, size)
+	n, err := m.MarshalTo(dAtA)
+	if err != nil {
+		return nil, err
+	}
+	return dAtA[:n], nil
+}
+
+func (m *WorkerRecord) MarshalTo(dAtA []byte) (int, error) {
+	var i int
+	_ = i
+	var l int
+	_ = l
+	if len(m.ID) > 0 {
+		dAtA[i] = 0xa
+		i++
+		i = encodeVarintControl(dAtA, i, uint64(len(m.ID)))
+		i += copy(dAtA[i:], m.ID)
+	}
+	if len(m.Labels) > 0 {
+		for k, _ := range m.Labels {
+			dAtA[i] = 0x12
+			i++
+			v := m.Labels[k]
+			mapSize := 1 + len(k) + sovControl(uint64(len(k))) + 1 + len(v) + sovControl(uint64(len(v)))
+			i = encodeVarintControl(dAtA, i, uint64(mapSize))
+			dAtA[i] = 0xa
+			i++
+			i = encodeVarintControl(dAtA, i, uint64(len(k)))
+			i += copy(dAtA[i:], k)
+			dAtA[i] = 0x12
+			i++
+			i = encodeVarintControl(dAtA, i, uint64(len(v)))
+			i += copy(dAtA[i:], v)
+		}
+	}
+	return i, nil
+}
+
 func encodeFixed64Control(dAtA []byte, offset int, v uint64) int {
 	dAtA[offset] = uint8(v)
 	dAtA[offset+1] = uint8(v >> 8)
@@ -1617,6 +1815,48 @@ func (m *BytesMessage) Size() (n int) {
 	return n
 }
 
+func (m *ListWorkersRequest) Size() (n int) {
+	var l int
+	_ = l
+	if len(m.Filter) > 0 {
+		for _, s := range m.Filter {
+			l = len(s)
+			n += 1 + l + sovControl(uint64(l))
+		}
+	}
+	return n
+}
+
+func (m *ListWorkersResponse) Size() (n int) {
+	var l int
+	_ = l
+	if len(m.Record) > 0 {
+		for _, e := range m.Record {
+			l = e.Size()
+			n += 1 + l + sovControl(uint64(l))
+		}
+	}
+	return n
+}
+
+func (m *WorkerRecord) Size() (n int) {
+	var l int
+	_ = l
+	l = len(m.ID)
+	if l > 0 {
+		n += 1 + l + sovControl(uint64(l))
+	}
+	if len(m.Labels) > 0 {
+		for k, v := range m.Labels {
+			_ = k
+			_ = v
+			mapEntrySize := 1 + len(k) + sovControl(uint64(len(k))) + 1 + len(v) + sovControl(uint64(len(v)))
+			n += mapEntrySize + 1 + sovControl(uint64(mapEntrySize))
+		}
+	}
+	return n
+}
+
 func sovControl(x uint64) (n int) {
 	for {
 		n++
@@ -3703,6 +3943,361 @@ func (m *BytesMessage) Unmarshal(dAtA []byte) error {
 	}
 	return nil
 }
+func (m *ListWorkersRequest) Unmarshal(dAtA []byte) error {
+	l := len(dAtA)
+	iNdEx := 0
+	for iNdEx < l {
+		preIndex := iNdEx
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return ErrIntOverflowControl
+			}
+			if iNdEx >= l {
+				return io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= (uint64(b) & 0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		fieldNum := int32(wire >> 3)
+		wireType := int(wire & 0x7)
+		if wireType == 4 {
+			return fmt.Errorf("proto: ListWorkersRequest: wiretype end group for non-group")
+		}
+		if fieldNum <= 0 {
+			return fmt.Errorf("proto: ListWorkersRequest: illegal tag %d (wire type %d)", fieldNum, wire)
+		}
+		switch fieldNum {
+		case 1:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Filter", wireType)
+			}
+			var stringLen uint64
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowControl
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				stringLen |= (uint64(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			intStringLen := int(stringLen)
+			if intStringLen < 0 {
+				return ErrInvalidLengthControl
+			}
+			postIndex := iNdEx + intStringLen
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Filter = append(m.Filter, string(dAtA[iNdEx:postIndex]))
+			iNdEx = postIndex
+		default:
+			iNdEx = preIndex
+			skippy, err := skipControl(dAtA[iNdEx:])
+			if err != nil {
+				return err
+			}
+			if skippy < 0 {
+				return ErrInvalidLengthControl
+			}
+			if (iNdEx + skippy) > l {
+				return io.ErrUnexpectedEOF
+			}
+			iNdEx += skippy
+		}
+	}
+
+	if iNdEx > l {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+func (m *ListWorkersResponse) Unmarshal(dAtA []byte) error {
+	l := len(dAtA)
+	iNdEx := 0
+	for iNdEx < l {
+		preIndex := iNdEx
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return ErrIntOverflowControl
+			}
+			if iNdEx >= l {
+				return io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= (uint64(b) & 0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		fieldNum := int32(wire >> 3)
+		wireType := int(wire & 0x7)
+		if wireType == 4 {
+			return fmt.Errorf("proto: ListWorkersResponse: wiretype end group for non-group")
+		}
+		if fieldNum <= 0 {
+			return fmt.Errorf("proto: ListWorkersResponse: illegal tag %d (wire type %d)", fieldNum, wire)
+		}
+		switch fieldNum {
+		case 1:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Record", wireType)
+			}
+			var msglen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowControl
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				msglen |= (int(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if msglen < 0 {
+				return ErrInvalidLengthControl
+			}
+			postIndex := iNdEx + msglen
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Record = append(m.Record, &WorkerRecord{})
+			if err := m.Record[len(m.Record)-1].Unmarshal(dAtA[iNdEx:postIndex]); err != nil {
+				return err
+			}
+			iNdEx = postIndex
+		default:
+			iNdEx = preIndex
+			skippy, err := skipControl(dAtA[iNdEx:])
+			if err != nil {
+				return err
+			}
+			if skippy < 0 {
+				return ErrInvalidLengthControl
+			}
+			if (iNdEx + skippy) > l {
+				return io.ErrUnexpectedEOF
+			}
+			iNdEx += skippy
+		}
+	}
+
+	if iNdEx > l {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+func (m *WorkerRecord) Unmarshal(dAtA []byte) error {
+	l := len(dAtA)
+	iNdEx := 0
+	for iNdEx < l {
+		preIndex := iNdEx
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return ErrIntOverflowControl
+			}
+			if iNdEx >= l {
+				return io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= (uint64(b) & 0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		fieldNum := int32(wire >> 3)
+		wireType := int(wire & 0x7)
+		if wireType == 4 {
+			return fmt.Errorf("proto: WorkerRecord: wiretype end group for non-group")
+		}
+		if fieldNum <= 0 {
+			return fmt.Errorf("proto: WorkerRecord: illegal tag %d (wire type %d)", fieldNum, wire)
+		}
+		switch fieldNum {
+		case 1:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field ID", wireType)
+			}
+			var stringLen uint64
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowControl
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				stringLen |= (uint64(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			intStringLen := int(stringLen)
+			if intStringLen < 0 {
+				return ErrInvalidLengthControl
+			}
+			postIndex := iNdEx + intStringLen
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.ID = string(dAtA[iNdEx:postIndex])
+			iNdEx = postIndex
+		case 2:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Labels", wireType)
+			}
+			var msglen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowControl
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				msglen |= (int(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if msglen < 0 {
+				return ErrInvalidLengthControl
+			}
+			postIndex := iNdEx + msglen
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			var keykey uint64
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowControl
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				keykey |= (uint64(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			var stringLenmapkey uint64
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowControl
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				stringLenmapkey |= (uint64(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			intStringLenmapkey := int(stringLenmapkey)
+			if intStringLenmapkey < 0 {
+				return ErrInvalidLengthControl
+			}
+			postStringIndexmapkey := iNdEx + intStringLenmapkey
+			if postStringIndexmapkey > l {
+				return io.ErrUnexpectedEOF
+			}
+			mapkey := string(dAtA[iNdEx:postStringIndexmapkey])
+			iNdEx = postStringIndexmapkey
+			if m.Labels == nil {
+				m.Labels = make(map[string]string)
+			}
+			if iNdEx < postIndex {
+				var valuekey uint64
+				for shift := uint(0); ; shift += 7 {
+					if shift >= 64 {
+						return ErrIntOverflowControl
+					}
+					if iNdEx >= l {
+						return io.ErrUnexpectedEOF
+					}
+					b := dAtA[iNdEx]
+					iNdEx++
+					valuekey |= (uint64(b) & 0x7F) << shift
+					if b < 0x80 {
+						break
+					}
+				}
+				var stringLenmapvalue uint64
+				for shift := uint(0); ; shift += 7 {
+					if shift >= 64 {
+						return ErrIntOverflowControl
+					}
+					if iNdEx >= l {
+						return io.ErrUnexpectedEOF
+					}
+					b := dAtA[iNdEx]
+					iNdEx++
+					stringLenmapvalue |= (uint64(b) & 0x7F) << shift
+					if b < 0x80 {
+						break
+					}
+				}
+				intStringLenmapvalue := int(stringLenmapvalue)
+				if intStringLenmapvalue < 0 {
+					return ErrInvalidLengthControl
+				}
+				postStringIndexmapvalue := iNdEx + intStringLenmapvalue
+				if postStringIndexmapvalue > l {
+					return io.ErrUnexpectedEOF
+				}
+				mapvalue := string(dAtA[iNdEx:postStringIndexmapvalue])
+				iNdEx = postStringIndexmapvalue
+				m.Labels[mapkey] = mapvalue
+			} else {
+				var mapvalue string
+				m.Labels[mapkey] = mapvalue
+			}
+			iNdEx = postIndex
+		default:
+			iNdEx = preIndex
+			skippy, err := skipControl(dAtA[iNdEx:])
+			if err != nil {
+				return err
+			}
+			if skippy < 0 {
+				return ErrInvalidLengthControl
+			}
+			if (iNdEx + skippy) > l {
+				return io.ErrUnexpectedEOF
+			}
+			iNdEx += skippy
+		}
+	}
+
+	if iNdEx > l {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
 func skipControl(dAtA []byte) (n int, err error) {
 	l := len(dAtA)
 	iNdEx := 0
@@ -3811,70 +4406,75 @@ var (
 func init() { proto.RegisterFile("control.proto", fileDescriptorControl) }
 
 var fileDescriptorControl = []byte{
-	// 1027 bytes of a gzipped FileDescriptorProto
-	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x09, 0x6e, 0x88, 0x02, 0xff, 0xa4, 0x56, 0x5f, 0x6f, 0xe3, 0x44,
-	0x10, 0xc7, 0x4e, 0xea, 0xc4, 0xd3, 0xb4, 0x2a, 0x2b, 0x74, 0xb2, 0x02, 0xa4, 0xc1, 0xbc, 0x44,
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+	0xbd, 0x2e, 0xd9, 0xbb, 0xa5, 0x4a, 0x23, 0x5c, 0x98, 0x2a, 0x17, 0x6a, 0xa3, 0x29, 0x53, 0xb3,
+	0x43, 0x4f, 0x94, 0x5c, 0x94, 0x01, 0x0b, 0x2a, 0xc2, 0x44, 0xa5, 0xca, 0xc6, 0x5a, 0x90, 0x23,
+	0x65, 0x36, 0x87, 0x6f, 0x37, 0x52, 0x66, 0x6e, 0x45, 0x1a, 0x6a, 0xaf, 0x45, 0x43, 0xfd, 0xd6,
+	0x34, 0xf8, 0x7f, 0x5a, 0xd0, 0x98, 0x55, 0x79, 0x21, 0xbb, 0xd6, 0x6b, 0x67, 0x77, 0x21, 0x33,
+	0x95, 0xbb, 0x65, 0xe6, 0x3e, 0x38, 0x5c, 0x30, 0x12, 0x4e, 0x14, 0x47, 0x36, 0x36, 0x92, 0xec,
+	0x27, 0x13, 0x1e, 0x29, 0x86, 0x5a, 0x58, 0x2e, 0x7d, 0x1f, 0x5a, 0xfd, 0x13, 0x41, 0xf8, 0x2e,
+	0xe1, 0x72, 0x92, 0x4a, 0x6e, 0xc7, 0xa1, 0x08, 0xd5, 0x3d, 0x5a, 0x58, 0xad, 0xfd, 0x07, 0x80,
+	0x76, 0x62, 0x2e, 0x5e, 0x50, 0x76, 0x48, 0x18, 0xbf, 0xe8, 0xd1, 0x63, 0x17, 0x1e, 0x3d, 0xbb,
+	0xf0, 0xd6, 0x82, 0xb5, 0xe9, 0x52, 0x9f, 0x9d, 0x7b, 0xf6, 0x5c, 0xd0, 0x6d, 0xb4, 0xcb, 0xb9,
+	0x77, 0xcf, 0xaf, 0x16, 0xb4, 0x8a, 0x1b, 0xa5, 0xca, 0xee, 0x83, 0xb3, 0x13, 0x0e, 0x49, 0x92,
+	0xb7, 0xb1, 0xb5, 0xab, 0x81, 0x03, 0x6d, 0xac, 0x07, 0x99, 0xf1, 0xf4, 0xbe, 0x80, 0x66, 0x41,
+	0x7d, 0x9b, 0xe1, 0xb1, 0xfe, 0x9b, 0x0d, 0xb5, 0x4d, 0xfd, 0x62, 0x45, 0xcf, 0xa1, 0x31, 0x7b,
+	0xef, 0x21, 0xbf, 0x1c, 0xc7, 0xf9, 0x87, 0xa3, 0xf7, 0xc1, 0x95, 0x36, 0x26, 0x73, 0xdf, 0xc0,
+	0x92, 0x1a, 0x29, 0xa8, 0x7d, 0xf5, 0xa4, 0xf6, 0x56, 0x2f, 0xdd, 0x37, 0x48, 0xbb, 0xe0, 0x98,
+	0xf6, 0x70, 0x91, 0x69, 0x71, 0xf2, 0x78, 0x9d, 0xcb, 0x0d, 0x34, 0xd8, 0x23, 0x0b, 0xed, 0xce,
+	0x9e, 0x21, 0x17, 0x85, 0x56, 0x2c, 0x2b, 0xef, 0x9a, 0xfd, 0xae, 0xf5, 0xc8, 0x42, 0x3f, 0x40,
+	0xb3, 0x50, 0x38, 0xe8, 0xc3, 0xb2, 0x4b, 0xb9, 0x0a, 0xbd, 0x8f, 0xae, 0xb1, 0xd2, 0xc1, 0xf6,
+	0x5b, 0xaf, 0xce, 0xda, 0xd6, 0x5f, 0x67, 0x6d, 0xeb, 0xdf, 0xb3, 0xb6, 0x35, 0x74, 0xd4, 0x7f,
+	0xf4, 0xf1, 0xff, 0x01, 0x00, 0x00, 0xff, 0xff, 0x54, 0x2e, 0xae, 0xbd, 0x6b, 0x0c, 0x00, 0x00,
 }
diff --git a/api/services/control/control.proto b/api/services/control/control.proto
index 827042a0..6eac542a 100644
--- a/api/services/control/control.proto
+++ b/api/services/control/control.proto
@@ -15,10 +15,11 @@ service Control {
 	rpc Solve(SolveRequest) returns (SolveResponse);
 	rpc Status(StatusRequest) returns (stream StatusResponse);
 	rpc Session(stream BytesMessage) returns (stream BytesMessage);
+	rpc ListWorkers(ListWorkersRequest) returns (ListWorkersResponse);
 }
 
 message DiskUsageRequest {
-	string filter = 1;
+	string filter = 1; // FIXME: this should be containerd-compatible repeated string?
 }
 
 message DiskUsageResponse {
@@ -98,4 +99,17 @@ message VertexLog {
 
 message BytesMessage {
 	bytes data = 1;
-}
\ No newline at end of file
+}
+
+message ListWorkersRequest {
+	repeated string filter = 1; // containerd style
+}
+
+message ListWorkersResponse {
+	repeated WorkerRecord record = 1;
+}
+
+message WorkerRecord {
+	string ID = 1;
+	map<string, string> Labels = 2;
+}
diff --git a/client/workers.go b/client/workers.go
new file mode 100644
index 00000000..b4ccb82d
--- /dev/null
+++ b/client/workers.go
@@ -0,0 +1,49 @@
+package client
+
+import (
+	"context"
+
+	controlapi "github.com/moby/buildkit/api/services/control"
+	"github.com/pkg/errors"
+)
+
+type WorkerInfo struct {
+	ID     string
+	Labels map[string]string
+}
+
+func (c *Client) ListWorkers(ctx context.Context, opts ...ListWorkersOption) ([]*WorkerInfo, error) {
+	info := &ListWorkersInfo{}
+	for _, o := range opts {
+		o(info)
+	}
+
+	req := &controlapi.ListWorkersRequest{Filter: info.Filter}
+	resp, err := c.controlClient().ListWorkers(ctx, req)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to list workers")
+	}
+
+	var wi []*WorkerInfo
+
+	for _, w := range resp.Record {
+		wi = append(wi, &WorkerInfo{
+			ID:     w.ID,
+			Labels: w.Labels,
+		})
+	}
+
+	return wi, nil
+}
+
+type ListWorkersOption func(*ListWorkersInfo)
+
+type ListWorkersInfo struct {
+	Filter []string
+}
+
+func WithWorkerFilter(f []string) ListWorkersOption {
+	return func(wi *ListWorkersInfo) {
+		wi.Filter = f
+	}
+}
diff --git a/cmd/buildctl/debug.go b/cmd/buildctl/debug.go
index e880ba70..a6a33b6f 100644
--- a/cmd/buildctl/debug.go
+++ b/cmd/buildctl/debug.go
@@ -11,5 +11,6 @@ var debugCommand = cli.Command{
 	Subcommands: []cli.Command{
 		debug.DumpLLBCommand,
 		debug.DumpMetadataCommand,
+		debug.WorkersCommand,
 	},
 }
diff --git a/cmd/buildctl/debug/workers.go b/cmd/buildctl/debug/workers.go
new file mode 100644
index 00000000..f8edcc4b
--- /dev/null
+++ b/cmd/buildctl/debug/workers.go
@@ -0,0 +1,88 @@
+package debug
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"text/tabwriter"
+
+	"github.com/moby/buildkit/client"
+	"github.com/moby/buildkit/util/appcontext"
+	"github.com/urfave/cli"
+)
+
+var WorkersCommand = cli.Command{
+	Name:   "workers",
+	Usage:  "list workers",
+	Action: listWorkers,
+	Flags: []cli.Flag{
+		cli.StringSliceFlag{
+			Name:  "filter, f",
+			Usage: "containerd-style filter string slice",
+		},
+		cli.BoolFlag{
+			Name:  "verbose, v",
+			Usage: "Verbose output",
+		},
+	},
+}
+
+func resolveClient(c *cli.Context) (*client.Client, error) {
+	return client.New(c.GlobalString("addr"), client.WithBlock())
+}
+
+func listWorkers(clicontext *cli.Context) error {
+	c, err := resolveClient(clicontext)
+	if err != nil {
+		return err
+	}
+
+	workers, err := c.ListWorkers(appcontext.Context(), client.WithWorkerFilter(clicontext.StringSlice("filter")))
+	if err != nil {
+		return err
+	}
+	tw := tabwriter.NewWriter(os.Stdout, 1, 8, 1, '\t', 0)
+
+	if clicontext.Bool("verbose") {
+		printWorkersVerbose(tw, workers)
+	} else {
+		printWorkersTable(tw, workers)
+	}
+	return nil
+}
+
+func printWorkersVerbose(tw *tabwriter.Writer, winfo []*client.WorkerInfo) {
+	for _, wi := range winfo {
+		fmt.Fprintf(tw, "ID:\t%s\n", wi.ID)
+		fmt.Fprintf(tw, "Labels:\n")
+		for _, k := range sortedKeys(wi.Labels) {
+			v := wi.Labels[k]
+			fmt.Fprintf(tw, "\t%s:\t%s\n", k, v)
+		}
+		fmt.Fprintf(tw, "\n")
+	}
+
+	tw.Flush()
+}
+
+func printWorkersTable(tw *tabwriter.Writer, winfo []*client.WorkerInfo) {
+	fmt.Fprintln(tw, "ID")
+
+	for _, wi := range winfo {
+		id := wi.ID
+		fmt.Fprintf(tw, "%s\n", id)
+	}
+
+	tw.Flush()
+}
+
+func sortedKeys(m map[string]string) []string {
+	s := make([]string, len(m))
+	i := 0
+	for k := range m {
+		s[i] = k
+		i++
+	}
+	sort.Strings(s)
+	return s
+}
diff --git a/cmd/buildkitd/main.go b/cmd/buildkitd/main.go
index ed95ad38..1ae07594 100644
--- a/cmd/buildkitd/main.go
+++ b/cmd/buildkitd/main.go
@@ -256,19 +256,20 @@ func newController(c *cli.Context, root string) (*control.Controller, error) {
 
 func newWorkerController(c *cli.Context, wiOpt workerInitializerOpt) (*worker.Controller, error) {
 	wc := &worker.Controller{}
+	nWorkers := 0
 	for _, wi := range workerInitializers {
 		ws, err := wi.fn(c, wiOpt)
 		if err != nil {
 			return nil, err
 		}
 		for _, w := range ws {
-			logrus.Infof("found worker %q", w.Name())
+			logrus.Infof("found worker %q, labels=%v", w.ID(), w.Labels())
 			if err = wc.Add(w); err != nil {
 				return nil, err
 			}
+			nWorkers++
 		}
 	}
-	nWorkers := len(wc.GetAll())
 	if nWorkers == 0 {
 		return nil, errors.New("no worker found, rebuild the buildkit daemon?")
 	}
@@ -276,7 +277,19 @@ func newWorkerController(c *cli.Context, wiOpt workerInitializerOpt) (*worker.Co
 	if err != nil {
 		return nil, err
 	}
-	logrus.Infof("found %d workers, default=%q", nWorkers, defaultWorker.Name)
+	logrus.Infof("found %d workers, default=%q", nWorkers, defaultWorker.ID())
 	logrus.Warn("currently, only the default worker can be used.")
 	return wc, nil
 }
+
+func attrMap(sl []string) (map[string]string, error) {
+	m := map[string]string{}
+	for _, v := range sl {
+		parts := strings.SplitN(v, "=", 2)
+		if len(parts) != 2 {
+			return nil, errors.Errorf("invalid value %s", v)
+		}
+		m[parts[0]] = parts[1]
+	}
+	return m, nil
+}
diff --git a/cmd/buildkitd/main_containerd_worker.go b/cmd/buildkitd/main_containerd_worker.go
index 26b20dcb..6730939c 100644
--- a/cmd/buildkitd/main_containerd_worker.go
+++ b/cmd/buildkitd/main_containerd_worker.go
@@ -30,7 +30,12 @@ func init() {
 			Name:  "containerd-worker-addr",
 			Usage: "containerd socket",
 			Value: "/run/containerd/containerd.sock",
-		})
+		},
+		cli.StringSliceFlag{
+			Name:  "containerd-worker-labels",
+			Usage: "user-specific annotation labels (com.example.foo=bar)",
+		},
+	)
 	// TODO(AkihiroSuda): allow using multiple snapshotters. should be useful for some applications that does not work with the default overlay snapshotter. e.g. mysql (docker/for-linux#72)",
 }
 
@@ -43,7 +48,11 @@ func containerdWorkerInitializer(c *cli.Context, common workerInitializerOpt) ([
 	if (boolOrAuto == nil && !validContainerdSocket(socket)) || (boolOrAuto != nil && !*boolOrAuto) {
 		return nil, nil
 	}
-	opt, err := containerd.NewWorkerOpt(common.root, socket, ctd.DefaultSnapshotter)
+	labels, err := attrMap(c.GlobalStringSlice("containerd-worker-labels"))
+	if err != nil {
+		return nil, err
+	}
+	opt, err := containerd.NewWorkerOpt(common.root, socket, ctd.DefaultSnapshotter, labels)
 	if err != nil {
 		return nil, err
 	}
diff --git a/cmd/buildkitd/main_oci_worker.go b/cmd/buildkitd/main_oci_worker.go
index a86a4b5f..849b9964 100644
--- a/cmd/buildkitd/main_oci_worker.go
+++ b/cmd/buildkitd/main_oci_worker.go
@@ -22,7 +22,12 @@ func init() {
 			Name:  "oci-worker",
 			Usage: "enable oci workers (true/false/auto)",
 			Value: "auto",
-		})
+		},
+		cli.StringSliceFlag{
+			Name:  "oci-worker-labels",
+			Usage: "user-specific annotation labels (com.example.foo=bar)",
+		},
+	)
 	// TODO: allow multiple oci runtimes and snapshotters
 }
 
@@ -34,7 +39,11 @@ func ociWorkerInitializer(c *cli.Context, common workerInitializerOpt) ([]worker
 	if (boolOrAuto == nil && !validOCIBinary()) || (boolOrAuto != nil && !*boolOrAuto) {
 		return nil, nil
 	}
-	opt, err := runc.NewWorkerOpt(common.root)
+	labels, err := attrMap(c.GlobalStringSlice("oci-worker-labels"))
+	if err != nil {
+		return nil, err
+	}
+	opt, err := runc.NewWorkerOpt(common.root, labels)
 	if err != nil {
 		return nil, err
 	}
diff --git a/control/control.go b/control/control.go
index a097d0dd..8b2c13e1 100644
--- a/control/control.go
+++ b/control/control.go
@@ -51,7 +51,11 @@ func (c *Controller) Register(server *grpc.Server) error {
 
 func (c *Controller) DiskUsage(ctx context.Context, r *controlapi.DiskUsageRequest) (*controlapi.DiskUsageResponse, error) {
 	resp := &controlapi.DiskUsageResponse{}
-	for _, w := range c.opt.WorkerController.GetAll() {
+	workers, err := c.opt.WorkerController.List()
+	if err != nil {
+		return nil, err
+	}
+	for _, w := range workers {
 		du, err := w.DiskUsage(ctx, client.DiskUsageInfo{
 			Filter: r.Filter,
 		})
@@ -201,3 +205,18 @@ func (c *Controller) Session(stream controlapi.Control_SessionServer) error {
 	logrus.Debugf("session finished: %v", err)
 	return err
 }
+
+func (c *Controller) ListWorkers(ctx context.Context, r *controlapi.ListWorkersRequest) (*controlapi.ListWorkersResponse, error) {
+	resp := &controlapi.ListWorkersResponse{}
+	workers, err := c.opt.WorkerController.List(r.Filter...)
+	if err != nil {
+		return nil, err
+	}
+	for _, w := range workers {
+		resp.Record = append(resp.Record, &controlapi.WorkerRecord{
+			ID:     w.ID(),
+			Labels: w.Labels(),
+		})
+	}
+	return resp, nil
+}
diff --git a/solver/pb/ops.pb.go b/solver/pb/ops.pb.go
index b7fb57ca..cffaf6be 100644
--- a/solver/pb/ops.pb.go
+++ b/solver/pb/ops.pb.go
@@ -459,8 +459,7 @@ func (*BuildInput) Descriptor() ([]byte, []int) { return fileDescriptorOps, []in
 type OpMetadata struct {
 	IgnoreCache bool `protobuf:"varint,1,opt,name=ignore_cache,json=ignoreCache,proto3" json:"ignore_cache,omitempty"`
 	// Description can be used for keeping any text fields that builder doesn't parse
-	Description map[string]string `protobuf:"bytes,2,rep,name=description" json:"description,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
-	// TODO: add worker constraint, etc.
+	Description      map[string]string `protobuf:"bytes,2,rep,name=description" json:"description,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
 	WorkerConstraint *WorkerConstraint `protobuf:"bytes,3,opt,name=worker_constraint,json=workerConstraint" json:"worker_constraint,omitempty"`
 }
 
@@ -490,9 +489,9 @@ func (m *OpMetadata) GetWorkerConstraint() *WorkerConstraint {
 	return nil
 }
 
-// WorkerConstraint is WIP. Will be changed.
+// WorkerConstraint is experimental and likely to be changed.
 type WorkerConstraint struct {
-	WorkerType string `protobuf:"bytes,1,opt,name=worker_type,json=workerType,proto3" json:"worker_type,omitempty"`
+	Filter []string `protobuf:"bytes,1,rep,name=filter" json:"filter,omitempty"`
 }
 
 func (m *WorkerConstraint) Reset()                    { *m = WorkerConstraint{} }
@@ -500,11 +499,11 @@ func (m *WorkerConstraint) String() string            { return proto.CompactText
 func (*WorkerConstraint) ProtoMessage()               {}
 func (*WorkerConstraint) Descriptor() ([]byte, []int) { return fileDescriptorOps, []int{11} }
 
-func (m *WorkerConstraint) GetWorkerType() string {
+func (m *WorkerConstraint) GetFilter() []string {
 	if m != nil {
-		return m.WorkerType
+		return m.Filter
 	}
-	return ""
+	return nil
 }
 
 // Definition is the LLB definition structure with per-vertex metadata entries
@@ -1097,11 +1096,20 @@ func (m *WorkerConstraint) MarshalTo(dAtA []byte) (int, error) {
 	_ = i
 	var l int
 	_ = l
-	if len(m.WorkerType) > 0 {
-		dAtA[i] = 0xa
-		i++
-		i = encodeVarintOps(dAtA, i, uint64(len(m.WorkerType)))
-		i += copy(dAtA[i:], m.WorkerType)
+	if len(m.Filter) > 0 {
+		for _, s := range m.Filter {
+			dAtA[i] = 0xa
+			i++
+			l = len(s)
+			for l >= 1<<7 {
+				dAtA[i] = uint8(uint64(l)&0x7f | 0x80)
+				l >>= 7
+				i++
+			}
+			dAtA[i] = uint8(l)
+			i++
+			i += copy(dAtA[i:], s)
+		}
 	}
 	return i, nil
 }
@@ -1428,9 +1436,11 @@ func (m *OpMetadata) Size() (n int) {
 func (m *WorkerConstraint) Size() (n int) {
 	var l int
 	_ = l
-	l = len(m.WorkerType)
-	if l > 0 {
-		n += 1 + l + sovOps(uint64(l))
+	if len(m.Filter) > 0 {
+		for _, s := range m.Filter {
+			l = len(s)
+			n += 1 + l + sovOps(uint64(l))
+		}
 	}
 	return n
 }
@@ -3283,7 +3293,7 @@ func (m *WorkerConstraint) Unmarshal(dAtA []byte) error {
 		switch fieldNum {
 		case 1:
 			if wireType != 2 {
-				return fmt.Errorf("proto: wrong wireType = %d for field WorkerType", wireType)
+				return fmt.Errorf("proto: wrong wireType = %d for field Filter", wireType)
 			}
 			var stringLen uint64
 			for shift := uint(0); ; shift += 7 {
@@ -3308,7 +3318,7 @@ func (m *WorkerConstraint) Unmarshal(dAtA []byte) error {
 			if postIndex > l {
 				return io.ErrUnexpectedEOF
 			}
-			m.WorkerType = string(dAtA[iNdEx:postIndex])
+			m.Filter = append(m.Filter, string(dAtA[iNdEx:postIndex]))
 			iNdEx = postIndex
 		default:
 			iNdEx = preIndex
@@ -3639,58 +3649,58 @@ var (
 func init() { proto.RegisterFile("ops.proto", fileDescriptorOps) }
 
 var fileDescriptorOps = []byte{
-	// 845 bytes of a gzipped FileDescriptorProto
-	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xac, 0x55, 0xcd, 0x8e, 0x1b, 0x45,
-	0x10, 0xde, 0x19, 0xff, 0xc4, 0x53, 0xb3, 0x20, 0xd3, 0x44, 0x60, 0x59, 0x91, 0xd7, 0x0c, 0x08,
-	0x2d, 0x90, 0x9d, 0x95, 0x36, 0x12, 0x8a, 0x38, 0x44, 0x5a, 0xef, 0x46, 0xc2, 0xa0, 0xc8, 0x52,
-	0x83, 0xc4, 0x31, 0x1a, 0xcf, 0xb4, 0x9d, 0x51, 0xec, 0xe9, 0x56, 0x4f, 0x4f, 0x76, 0x7d, 0xe1,
-	0xc0, 0x13, 0x20, 0xf1, 0x16, 0xbc, 0x03, 0x9c, 0x73, 0xe4, 0x0a, 0x87, 0x80, 0x96, 0x67, 0xe0,
-	0x8e, 0xaa, 0xba, 0xed, 0x99, 0x2c, 0x41, 0xca, 0x0a, 0x4e, 0xae, 0xae, 0x9f, 0xaf, 0xaa, 0xbe,
-	0xaa, 0x1a, 0x43, 0x20, 0x55, 0x19, 0x2b, 0x2d, 0x8d, 0x64, 0xbe, 0x9a, 0x0f, 0x8f, 0x96, 0xb9,
-	0x79, 0x52, 0xcd, 0xe3, 0x54, 0xae, 0x8f, 0x97, 0x72, 0x29, 0x8f, 0xc9, 0x34, 0xaf, 0x16, 0xf4,
-	0xa2, 0x07, 0x49, 0x36, 0x24, 0xfa, 0xd9, 0x03, 0x7f, 0xa6, 0xd8, 0x7b, 0xd0, 0xcd, 0x0b, 0x55,
-	0x99, 0x72, 0xe0, 0x8d, 0x5b, 0x87, 0xe1, 0x49, 0x10, 0xab, 0x79, 0x3c, 0x45, 0x0d, 0x77, 0x06,
-	0x36, 0x86, 0xb6, 0xb8, 0x14, 0xe9, 0xc0, 0x1f, 0x7b, 0x87, 0xe1, 0x09, 0xa0, 0xc3, 0xc3, 0x4b,
-	0x91, 0xce, 0xd4, 0xe7, 0x7b, 0x9c, 0x2c, 0xec, 0x43, 0xe8, 0x96, 0xb2, 0xd2, 0xa9, 0x18, 0xb4,
-	0xc8, 0x67, 0x1f, 0x7d, 0xbe, 0x22, 0x0d, 0x79, 0x39, 0x2b, 0x22, 0xa5, 0x52, 0x6d, 0x06, 0xed,
-	0x1a, 0xe9, 0x4c, 0xaa, 0x8d, 0x45, 0x42, 0x0b, 0x7b, 0x1f, 0x3a, 0xf3, 0x2a, 0x5f, 0x65, 0x83,
-	0x0e, 0xb9, 0x84, 0xe8, 0x32, 0x41, 0x05, 0xf9, 0x58, 0xdb, 0xa4, 0x0d, 0xbe, 0x54, 0xd1, 0xb7,
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-	0x9c, 0x15, 0xf4, 0xd6, 0x8e, 0x02, 0x47, 0xcc, 0x9d, 0x97, 0xf7, 0x2b, 0xde, 0x32, 0x44, 0x15,
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-	0x03, 0x00, 0x00, 0xff, 0xff, 0x26, 0xbe, 0xb0, 0x53, 0x90, 0x07, 0x00, 0x00,
+	// 842 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xac, 0x55, 0xc1, 0x8e, 0x1b, 0x45,
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+	0x4f, 0xb6, 0x3e, 0x3e, 0xb8, 0xb8, 0x66, 0x19, 0x3d, 0x84, 0xc1, 0xf5, 0x18, 0x37, 0xd2, 0xeb,
+	0x1e, 0x0c, 0xae, 0x47, 0x61, 0x77, 0x20, 0x98, 0xcb, 0xa5, 0xa1, 0xb1, 0xc3, 0xaf, 0x92, 0xbb,
+	0xc5, 0xbf, 0x7a, 0x00, 0xcd, 0x88, 0x60, 0x18, 0x9c, 0x1f, 0xc4, 0xec, 0xda, 0x79, 0x59, 0x42,
+	0x7f, 0xe5, 0x2a, 0x77, 0x7a, 0xdc, 0x7d, 0x75, 0xac, 0x92, 0x8d, 0x30, 0x94, 0xa8, 0xfd, 0x92,
+	0x7f, 0xf7, 0xfb, 0x8d, 0xbe, 0xe4, 0xdb, 0x08, 0xa3, 0xaf, 0xe0, 0xad, 0x57, 0xe8, 0xde, 0x70,
+	0xe2, 0x9a, 0xee, 0xb4, 0x74, 0x98, 0x0e, 0x5e, 0x5c, 0x8d, 0xbd, 0x5f, 0xae, 0xc6, 0xde, 0x1f,
+	0x57, 0x63, 0xef, 0xfb, 0x3f, 0xc7, 0x3b, 0xb3, 0x80, 0xfe, 0x47, 0x3f, 0xfd, 0x3b, 0x00, 0x00,
+	0xff, 0xff, 0x99, 0xd2, 0xfe, 0xe4, 0x87, 0x07, 0x00, 0x00,
 }
diff --git a/solver/pb/ops.proto b/solver/pb/ops.proto
index 9c5f4296..912f82c8 100644
--- a/solver/pb/ops.proto
+++ b/solver/pb/ops.proto
@@ -74,14 +74,12 @@ message OpMetadata {
 	bool ignore_cache = 1;
 	// Description can be used for keeping any text fields that builder doesn't parse
 	map<string, string> description = 2;  
-	// TODO: add worker constraint, etc.
 	WorkerConstraint worker_constraint = 3;
 }
 
-// WorkerConstraint is WIP. Will be changed.
+// WorkerConstraint is experimental and likely to be changed.
 message WorkerConstraint {
-	string worker_type = 1; // e.g. "runc", "containerd"...? also we will have worker_brand, arch, os, labels...
-// TODO: distributed mode
+	repeated string filter = 1; // containerd-style filter
 }
 
 // Definition is the LLB definition structure with per-vertex metadata entries
diff --git a/worker/base/worker.go b/worker/base/worker.go
index 1ac3c96e..3c27ed5d 100644
--- a/worker/base/worker.go
+++ b/worker/base/worker.go
@@ -2,6 +2,10 @@ package base
 
 import (
 	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"runtime"
 
 	"github.com/containerd/containerd/content"
 	"github.com/containerd/containerd/diff"
@@ -18,6 +22,7 @@ import (
 	imageexporter "github.com/moby/buildkit/exporter/containerimage"
 	localexporter "github.com/moby/buildkit/exporter/local"
 	ociexporter "github.com/moby/buildkit/exporter/oci"
+	"github.com/moby/buildkit/identity"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/snapshot/blobmapping"
 	"github.com/moby/buildkit/solver"
@@ -39,7 +44,8 @@ import (
 // WorkerOpt is specific to a worker.
 // See also CommonOpt.
 type WorkerOpt struct {
-	Name            string
+	ID              string
+	Labels          map[string]string
 	SessionManager  *session.Manager
 	MetadataStore   *metadata.Store
 	Executor        executor.Executor
@@ -47,12 +53,11 @@ type WorkerOpt struct {
 	ContentStore    content.Store
 	Applier         diff.Differ
 	Differ          diff.Differ
-	ImageStore      images.Store
+	ImageStore      images.Store // optional
 }
 
 // Worker is a local worker instance with dedicated snapshotter, cache, and so on.
 // TODO: s/Worker/OpWorker/g ?
-// FIXME: Worker should be rather an interface
 type Worker struct {
 	WorkerOpt
 	Snapshotter   ctdsnapshot.Snapshotter // blobmapping snapshotter
@@ -215,6 +220,14 @@ func NewWorker(opt WorkerOpt) (*Worker, error) {
 	}, nil
 }
 
+func (w *Worker) ID() string {
+	return w.WorkerOpt.ID
+}
+
+func (w *Worker) Labels() map[string]string {
+	return w.WorkerOpt.Labels
+}
+
 func (w *Worker) ResolveOp(v solver.Vertex, s worker.SubBuilder) (solver.Op, error) {
 	switch op := v.Sys().(type) {
 	case *pb.Op_Source:
@@ -232,7 +245,7 @@ func (w *Worker) ResolveImageConfig(ctx context.Context, ref string) (digest.Dig
 	// ImageSource is typically source/containerimage
 	resolveImageConfig, ok := w.ImageSource.(resolveImageConfig)
 	if !ok {
-		return "", nil, errors.Errorf("worker %q does not implement ResolveImageConfig", w.Name())
+		return "", nil, errors.Errorf("worker %q does not implement ResolveImageConfig", w.ID())
 	}
 	return resolveImageConfig.ResolveImageConfig(ctx, ref)
 }
@@ -254,10 +267,6 @@ func (w *Worker) DiskUsage(ctx context.Context, opt client.DiskUsageInfo) ([]*cl
 	return w.CacheManager.DiskUsage(ctx, opt)
 }
 
-func (w *Worker) Name() string {
-	return w.WorkerOpt.Name
-}
-
 func (w *Worker) Exporter(name string) (exporter.Exporter, error) {
 	exp, ok := w.Exporters[name]
 	if !ok {
@@ -269,3 +278,36 @@ func (w *Worker) Exporter(name string) (exporter.Exporter, error) {
 func (w *Worker) InstructionCache() instructioncache.InstructionCache {
 	return w.cache
 }
+
+// utility function. could be moved to the constructor logic?
+func Labels(executor, snapshotter string) map[string]string {
+	hostname, err := os.Hostname()
+	if err != nil {
+		hostname = "unknown"
+	}
+	labels := map[string]string{
+		worker.LabelOS:          runtime.GOOS,
+		worker.LabelArch:        runtime.GOARCH,
+		worker.LabelExecutor:    executor,
+		worker.LabelSnapshotter: snapshotter,
+		worker.LabelHostname:    hostname,
+	}
+	return labels
+}
+
+// ID reads the worker id from the `workerid` file.
+// If not exist, it creates a random one,
+func ID(root string) (string, error) {
+	f := filepath.Join(root, "workerid")
+	b, err := ioutil.ReadFile(f)
+	if err != nil {
+		if os.IsNotExist(err) {
+			id := identity.NewID()
+			err := ioutil.WriteFile(f, []byte(id), 0400)
+			return id, err
+		} else {
+			return "", err
+		}
+	}
+	return string(b), nil
+}
diff --git a/worker/base/worker_test.go b/worker/base/worker_test.go
new file mode 100644
index 00000000..a80372ba
--- /dev/null
+++ b/worker/base/worker_test.go
@@ -0,0 +1,34 @@
+package base
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestID(t *testing.T) {
+	t.Parallel()
+	tmpdir, err := ioutil.TempDir("", "worker-base-test-id")
+	require.NoError(t, err)
+
+	id0, err := ID(tmpdir)
+	require.NoError(t, err)
+
+	id1, err := ID(tmpdir)
+	require.NoError(t, err)
+
+	require.Equal(t, id0, id1)
+
+	// reset tmpdir
+	require.NoError(t, os.RemoveAll(tmpdir))
+	require.NoError(t, os.MkdirAll(tmpdir, 0700))
+
+	id2, err := ID(tmpdir)
+	require.NoError(t, err)
+
+	require.NotEqual(t, id0, id2)
+
+	require.NoError(t, os.RemoveAll(tmpdir))
+}
diff --git a/worker/containerd/containerd.go b/worker/containerd/containerd.go
index cba5a159..d18b4385 100644
--- a/worker/containerd/containerd.go
+++ b/worker/containerd/containerd.go
@@ -19,17 +19,17 @@ import (
 // NewWorkerOpt creates a WorkerOpt.
 // But it does not set the following fields:
 //  - SessionManager
-func NewWorkerOpt(root string, address, snapshotterName string, opts ...containerd.ClientOpt) (base.WorkerOpt, error) {
+func NewWorkerOpt(root string, address, snapshotterName string, labels map[string]string, opts ...containerd.ClientOpt) (base.WorkerOpt, error) {
 	// TODO: take lock to make sure there are no duplicates
 	opts = append([]containerd.ClientOpt{containerd.WithDefaultNamespace("buildkit")}, opts...)
 	client, err := containerd.New(address, opts...)
 	if err != nil {
 		return base.WorkerOpt{}, errors.Wrapf(err, "failed to connect client to %q . make sure containerd is running", address)
 	}
-	return newContainerd(root, client, snapshotterName)
+	return newContainerd(root, client, snapshotterName, labels)
 }
 
-func newContainerd(root string, client *containerd.Client, snapshotterName string) (base.WorkerOpt, error) {
+func newContainerd(root string, client *containerd.Client, snapshotterName string, labels map[string]string) (base.WorkerOpt, error) {
 	if strings.Contains(snapshotterName, "/") {
 		return base.WorkerOpt{}, errors.Errorf("bad snapshotter name: %q", snapshotterName)
 	}
@@ -44,8 +44,18 @@ func newContainerd(root string, client *containerd.Client, snapshotterName strin
 		return base.WorkerOpt{}, err
 	}
 	df := client.DiffService()
+	// TODO: should use containerd daemon instance ID (containerd/containerd#1862)?
+	id, err := base.ID(root)
+	if err != nil {
+		return base.WorkerOpt{}, err
+	}
+	xlabels := base.Labels("containerd", snapshotterName)
+	for k, v := range labels {
+		xlabels[k] = v
+	}
 	opt := base.WorkerOpt{
-		Name:            name,
+		ID:              id,
+		Labels:          xlabels,
 		MetadataStore:   md,
 		Executor:        containerdexecutor.New(client, root),
 		BaseSnapshotter: client.SnapshotService(snapshotterName),
diff --git a/worker/filter.go b/worker/filter.go
new file mode 100644
index 00000000..c94a6265
--- /dev/null
+++ b/worker/filter.go
@@ -0,0 +1,33 @@
+package worker
+
+import (
+	"strings"
+
+	"github.com/containerd/containerd/filters"
+)
+
+func adaptWorker(w Worker) filters.Adaptor {
+	return filters.AdapterFunc(func(fieldpath []string) (string, bool) {
+		if len(fieldpath) == 0 {
+			return "", false
+		}
+
+		switch fieldpath[0] {
+		case "id":
+			return w.ID(), len(w.ID()) > 0
+		case "labels":
+			return checkMap(fieldpath[1:], w.Labels())
+		}
+
+		return "", false
+	})
+}
+
+func checkMap(fieldpath []string, m map[string]string) (string, bool) {
+	if len(m) == 0 {
+		return "", false
+	}
+
+	value, ok := m[strings.Join(fieldpath, ".")]
+	return value, ok
+}
diff --git a/worker/runc/runc.go b/worker/runc/runc.go
index d0a38351..a54be443 100644
--- a/worker/runc/runc.go
+++ b/worker/runc/runc.go
@@ -23,9 +23,9 @@ import (
 // NewWorkerOpt creates a WorkerOpt.
 // But it does not set the following fields:
 //  - SessionManager
-func NewWorkerOpt(root string) (base.WorkerOpt, error) {
+func NewWorkerOpt(root string, labels map[string]string) (base.WorkerOpt, error) {
 	var opt base.WorkerOpt
-	name := "runc-overlay"
+	name := "runc-overlayfs"
 	root = filepath.Join(root, name)
 	if err := os.MkdirAll(root, 0700); err != nil {
 		return opt, err
@@ -54,7 +54,7 @@ func NewWorkerOpt(root string) (base.WorkerOpt, error) {
 	}
 
 	mdb := ctdmetadata.NewDB(db, c, map[string]ctdsnapshot.Snapshotter{
-		"overlay": s,
+		"overlayfs": s,
 	})
 	if err := mdb.Init(context.TODO()); err != nil {
 		return opt, err
@@ -68,11 +68,20 @@ func NewWorkerOpt(root string) (base.WorkerOpt, error) {
 
 	// TODO: call mdb.GarbageCollect . maybe just inject it into nsSnapshotter.Remove and csContent.Delete
 
+	id, err := base.ID(root)
+	if err != nil {
+		return opt, err
+	}
+	xlabels := base.Labels("oci", "overlayfs")
+	for k, v := range labels {
+		xlabels[k] = v
+	}
 	opt = base.WorkerOpt{
-		Name:            name,
+		ID:              id,
+		Labels:          xlabels,
 		MetadataStore:   md,
 		Executor:        exe,
-		BaseSnapshotter: &nsSnapshotter{mdb.Snapshotter("overlay")},
+		BaseSnapshotter: &nsSnapshotter{mdb.Snapshotter("overlayfs")},
 		ContentStore:    c,
 		Applier:         df,
 		Differ:          df,
diff --git a/worker/runc/runc_test.go b/worker/runc/runc_test.go
index 446a4aeb..1c77c404 100644
--- a/worker/runc/runc_test.go
+++ b/worker/runc/runc_test.go
@@ -38,7 +38,7 @@ func TestRuncWorker(t *testing.T) {
 	require.NoError(t, err)
 	defer os.RemoveAll(tmpdir)
 
-	workerOpt, err := NewWorkerOpt(tmpdir)
+	workerOpt, err := NewWorkerOpt(tmpdir, nil)
 	require.NoError(t, err)
 
 	workerOpt.SessionManager, err = session.NewManager()
diff --git a/worker/worker.go b/worker/worker.go
index 9759e209..71f85b8b 100644
--- a/worker/worker.go
+++ b/worker/worker.go
@@ -18,6 +18,9 @@ type SubBuilder interface {
 }
 
 type Worker interface {
+	// ID needs to be unique in the cluster
+	ID() string
+	Labels() map[string]string
 	InstructionCache() instructioncache.InstructionCache
 	// ResolveOp resolves Vertex.Sys() to Op implementation. SubBuilder is needed for pb.Op_Build.
 	ResolveOp(v types.Vertex, s SubBuilder) (types.Op, error)
@@ -25,6 +28,15 @@ type Worker interface {
 	// Exec is similar to executor.Exec but without []mount.Mount
 	Exec(ctx context.Context, meta executor.Meta, rootFS cache.ImmutableRef, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error
 	DiskUsage(ctx context.Context, opt client.DiskUsageInfo) ([]*client.UsageInfo, error)
-	Name() string
 	Exporter(name string) (exporter.Exporter, error)
 }
+
+// Pre-defined label keys
+const (
+	labelPrefix      = "org.mobyproject.buildkit.worker."
+	LabelOS          = labelPrefix + "os"          // GOOS
+	LabelArch        = labelPrefix + "arch"        // GOARCH
+	LabelExecutor    = labelPrefix + "executor"    // "oci" or "containerd"
+	LabelSnapshotter = labelPrefix + "snapshotter" // containerd snapshotter name ("overlay", "naive", ...)
+	LabelHostname    = labelPrefix + "hostname"
+)
diff --git a/worker/workercontroller.go b/worker/workercontroller.go
index a74c29db..62ab8ff1 100644
--- a/worker/workercontroller.go
+++ b/worker/workercontroller.go
@@ -3,6 +3,7 @@ package worker
 import (
 	"sync"
 
+	"github.com/containerd/containerd/filters"
 	"github.com/pkg/errors"
 )
 
@@ -22,12 +23,22 @@ func (c *Controller) Add(w Worker) error {
 	return nil
 }
 
-// GetAll returns all local workers
-func (c *Controller) GetAll() []Worker {
+// List lists workers
+func (c *Controller) List(filterStrings ...string) ([]Worker, error) {
+	filter, err := filters.ParseAll(filterStrings...)
+	if err != nil {
+		return nil, err
+	}
 	c.mu.Lock()
-	workers := c.workers
+	allWorkers := c.workers
 	c.mu.Unlock()
-	return workers
+	var workers []Worker
+	for _, w := range allWorkers {
+		if filter.Match(adaptWorker(w)) {
+			workers = append(workers, w)
+		}
+	}
+	return workers, nil
 }
 
 // GetDefault returns the default local worker