feat(scale): store container spec in local machine.db sqlite

internal/machine/db.go

@@ -0,0 +1,42 @@
+package machine
+
+import (
+	"fmt"
+
+	"github.com/jmoiron/sqlx"
+	_ "modernc.org/sqlite"
+)
+
+const DBFileName = "machine.db"
+
+// NewDB creates a new connection to machine SQLite database and runs schema migrations if necessary.
+func NewDB(path string) (*sqlx.DB, error) {
+	// - Write-Ahead Logging (WAL) mode for better read/write performance.
+	// - Busy timeout (5s) to make concurrent writes wait on each other instead of failing immediately.
+	conn := path + "?_pragma=journal_mode=WAL&_pragma=synchronous=NORMAL&_pragma=busy_timeout=5000&_time_format=sqlite"
+	db, err := sqlx.Connect("sqlite", conn)
+	if err != nil {
+		return nil, fmt.Errorf("connect to SQLite database '%s': %w", conn, err)
+	}
+
+	schema := `
+	CREATE TABLE IF NOT EXISTS containers (
+	    id TEXT NOT NULL PRIMARY KEY,
+	    service_id TEXT NOT NULL,
+	    service_name TEXT AS (json_extract(service_spec, '$.Name')),
+	    service_spec TEXT NOT NULL CHECK (json_valid(service_spec)),
+	    -- 'subsecond' modifier is used to store timestamps with millisecond precision.
+	    created_at TIMESTAMP NOT NULL DEFAULT (datetime('subsecond')),
+	    updated_at TIMESTAMP NOT NULL DEFAULT (datetime('subsecond'))
+	);
+
+	CREATE INDEX IF NOT EXISTS idx_containers_service_id ON containers (service_id);
+	CREATE INDEX IF NOT EXISTS idx_containers_service_name ON containers (service_name);
+    `
+
+	if _, err = db.Exec(schema); err != nil {
+		return nil, fmt.Errorf("create schema: %w", err)
+	}
+
+	return db, nil
+}