feat: add GET /log-demo route showing structured logging to Kibana

src/app.test.ts

@@ -67,3 +67,26 @@ describe("routes", () => {
     expect(b.headers["x-request-id"]).toMatch(/^[0-9a-f-]{36}$/);
   });
 });
+
+describe("log-demo", () => {
+  it("logs one JSON line with demo fields and the request id", async () => {
+    const lines: Record<string, unknown>[] = [];
+    const captured = pino(
+      { base: { service: "test-svc" } },
+      { write: (l: string) => lines.push(JSON.parse(l)) },
+    );
+    const app = createApp({ config: parseConfig(base), logger: captured });
+    const res = await request(app)
+      .get("/log-demo?msg=hello")
+      .set("X-Request-Id", "rid-demo");
+    expect(res.status).toBe(200);
+    expect(res.body).toMatchObject({ logged: true, text: "hello" });
+    const line = lines.find((l) => l.msg === "log-demo");
+    expect(line).toMatchObject({
+      service: "test-svc",
+      demo: true,
+      text: "hello",
+      req: { id: "rid-demo" },
+    });
+  });
+});

src/app.ts

@@ -6,6 +6,7 @@ import type { Config } from "./lib/config.js";
 import type { Db } from "./lib/db.js";
 import type { Cache } from "./lib/redis.js";
 import { healthRouter } from "./routes/health.js";
+import { logDemoRouter } from "./routes/log-demo.js";
 import { rootRouter } from "./routes/root.js";
 
 export interface Deps {
@@ -43,6 +44,7 @@ export function createApp({ config, logger, db, cache }: Deps) {
 
   app.use(healthRouter({ db, cache }));
   app.use(rootRouter({ config, db, cache }));
+  app.use(logDemoRouter());
 
   // Express identifies error handlers by arity; keep all four args.
   // eslint-disable-next-line @typescript-eslint/no-unused-vars

src/routes/log-demo.ts

@@ -0,0 +1,17 @@
+import { Router } from "express";
+
+// Developer-story demo for the logging pipeline: every field in the first
+// argument to req.log.* becomes a queryable field in Kibana (data view kube-*).
+// The message string always wins over a `msg` key in the object, so the
+// caller's text goes in `text`.
+export function logDemoRouter(): Router {
+  const router = Router();
+
+  router.get("/log-demo", (req, res) => {
+    const text = typeof req.query.msg === "string" ? req.query.msg : "";
+    req.log.info({ demo: true, text }, "log-demo");
+    res.json({ logged: true, text, requestId: req.id });
+  });
+
+  return router;
+}