diff --git a/internal/updater/swarm_executor.go b/internal/updater/swarm_executor.go
new file mode 100644
index 0000000..a007792
--- /dev/null
+++ b/internal/updater/swarm_executor.go
@@ -0,0 +1,52 @@
+package updater
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/docker/docker/api/types/swarm"
+	"github.com/shcizo/package-updater/internal/discovery"
+)
+
+// SwarmDockerClient is the subset of the Docker SDK SwarmExecutor depends
+// on. Defined as an interface so tests can supply a fake.
+type SwarmDockerClient interface {
+	ServiceInspectWithRaw(ctx context.Context, serviceID string, opts swarm.ServiceInspectOptions) (swarm.Service, []byte, error)
+	ServiceUpdate(ctx context.Context, serviceID string, version swarm.Version, service swarm.ServiceSpec, opts swarm.ServiceUpdateOptions) (swarm.ServiceUpdateResponse, error)
+}
+
+// SwarmExecutor updates a Swarm service's image via the Docker API,
+// equivalent to `docker service update --image`.
+type SwarmExecutor struct {
+	cli SwarmDockerClient
+}
+
+// NewSwarmExecutor returns an executor that drives Swarm service updates
+// through the Docker API.
+func NewSwarmExecutor(cli SwarmDockerClient) *SwarmExecutor {
+	return &SwarmExecutor{cli: cli}
+}
+
+// Execute inspects the service to get its current spec and version (required
+// by the Docker API as an optimistic-concurrency token), sets the new image
+// on the container spec, and calls ServiceUpdate. QueryRegistry is set so a
+// floating tag (e.g. ":latest") resolves to a fresh digest and actually
+// triggers a rolling update instead of being treated as unchanged.
+func (e *SwarmExecutor) Execute(ctx context.Context, job discovery.Job) error {
+	if job.Refused {
+		return fmt.Errorf("refused: %s", job.RefusedReason)
+	}
+
+	svc, _, err := e.cli.ServiceInspectWithRaw(ctx, job.ServiceID, swarm.ServiceInspectOptions{})
+	if err != nil {
+		return fmt.Errorf("inspect service %s: %w", job.ServiceID, err)
+	}
+
+	spec := svc.Spec
+	spec.TaskTemplate.ContainerSpec.Image = job.Image
+
+	if _, err := e.cli.ServiceUpdate(ctx, job.ServiceID, svc.Version, spec, swarm.ServiceUpdateOptions{QueryRegistry: true}); err != nil {
+		return fmt.Errorf("update service %s: %w", job.ServiceID, err)
+	}
+	return nil
+}
diff --git a/internal/updater/swarm_executor_test.go b/internal/updater/swarm_executor_test.go
new file mode 100644
index 0000000..253d139
--- /dev/null
+++ b/internal/updater/swarm_executor_test.go
@@ -0,0 +1,99 @@
+package updater_test
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/docker/docker/api/types/swarm"
+	"github.com/shcizo/package-updater/internal/discovery"
+	"github.com/shcizo/package-updater/internal/updater"
+	"github.com/stretchr/testify/require"
+)
+
+type fakeSwarmDockerClient struct {
+	inspectService swarm.Service
+	inspectErr     error
+	updateErr      error
+
+	inspectCalled         bool
+	updateCalled          bool
+	updateCalledServiceID string
+	updateCalledVersion   swarm.Version
+	updateCalledSpec      swarm.ServiceSpec
+	updateCalledOpts      swarm.ServiceUpdateOptions
+}
+
+func (f *fakeSwarmDockerClient) ServiceInspectWithRaw(_ context.Context, _ string, _ swarm.ServiceInspectOptions) (swarm.Service, []byte, error) {
+	f.inspectCalled = true
+	return f.inspectService, nil, f.inspectErr
+}
+
+func (f *fakeSwarmDockerClient) ServiceUpdate(_ context.Context, serviceID string, version swarm.Version, spec swarm.ServiceSpec, opts swarm.ServiceUpdateOptions) (swarm.ServiceUpdateResponse, error) {
+	f.updateCalled = true
+	f.updateCalledServiceID = serviceID
+	f.updateCalledVersion = version
+	f.updateCalledSpec = spec
+	f.updateCalledOpts = opts
+	return swarm.ServiceUpdateResponse{}, f.updateErr
+}
+
+func mkInspectService(version uint64, image string) swarm.Service {
+	return swarm.Service{
+		ID:   "svc-myapp",
+		Meta: swarm.Meta{Version: swarm.Version{Index: version}},
+		Spec: swarm.ServiceSpec{
+			Annotations:  swarm.Annotations{Name: "myapp_web"},
+			TaskTemplate: swarm.TaskSpec{ContainerSpec: &swarm.ContainerSpec{Image: image}},
+		},
+	}
+}
+
+func TestSwarmExecutor_UpdatesImageAndVersion(t *testing.T) {
+	fake := &fakeSwarmDockerClient{inspectService: mkInspectService(7, "registry.example.com/myapp:v1")}
+	e := updater.NewSwarmExecutor(fake)
+
+	job := discovery.Job{Service: "myapp_web", ServiceID: "svc-myapp", Image: "registry.example.com/myapp:v2"}
+	err := e.Execute(context.Background(), job)
+
+	require.NoError(t, err)
+	require.True(t, fake.updateCalled)
+	require.Equal(t, "svc-myapp", fake.updateCalledServiceID)
+	require.Equal(t, uint64(7), fake.updateCalledVersion.Index)
+	require.Equal(t, "registry.example.com/myapp:v2", fake.updateCalledSpec.TaskTemplate.ContainerSpec.Image)
+	require.True(t, fake.updateCalledOpts.QueryRegistry)
+}
+
+func TestSwarmExecutor_InspectError(t *testing.T) {
+	fake := &fakeSwarmDockerClient{inspectErr: errors.New("service not found")}
+	e := updater.NewSwarmExecutor(fake)
+
+	err := e.Execute(context.Background(), discovery.Job{ServiceID: "svc-missing", Image: "x:v2"})
+
+	require.Error(t, err)
+	require.False(t, fake.updateCalled)
+}
+
+func TestSwarmExecutor_UpdateError(t *testing.T) {
+	fake := &fakeSwarmDockerClient{
+		inspectService: mkInspectService(1, "registry.example.com/myapp:v1"),
+		updateErr:      errors.New("update rejected"),
+	}
+	e := updater.NewSwarmExecutor(fake)
+
+	err := e.Execute(context.Background(), discovery.Job{ServiceID: "svc-myapp", Image: "registry.example.com/myapp:v2"})
+
+	require.Error(t, err)
+}
+
+func TestSwarmExecutor_RefusedJobIsNotExecuted(t *testing.T) {
+	fake := &fakeSwarmDockerClient{}
+	e := updater.NewSwarmExecutor(fake)
+	job := discovery.Job{ServiceID: "svc-myapp", Image: "x:v2", Refused: true, RefusedReason: "not opted in"}
+
+	err := e.Execute(context.Background(), job)
+
+	require.Error(t, err)
+	require.False(t, fake.inspectCalled)
+	require.False(t, fake.updateCalled)
+}