diff --git a/internal/updater/executor.go b/internal/updater/executor.go
new file mode 100644
index 0000000..e767282
--- /dev/null
+++ b/internal/updater/executor.go
@@ -0,0 +1,15 @@
+// Package updater contains the FIFO job queue, the single worker that
+// drains it, and the abstraction over `docker compose` invocation.
+package updater
+
+import (
+	"context"
+
+	"github.com/shcizo/package-updater/internal/discovery"
+)
+
+// Executor runs `docker compose pull` then `up -d` for a single job.
+// Defined as an interface so the worker can be tested with a fake.
+type Executor interface {
+	Execute(ctx context.Context, job discovery.Job) error
+}