misc: initial working setup for metrics observabilit

backend/src/server/plugins/api-metrics.ts

@@ -0,0 +1,21 @@
+import opentelemetry from "@opentelemetry/api";
+import fp from "fastify-plugin";
+
+export const apiMetrics = fp(async (fastify) => {
+  const apiMeter = opentelemetry.metrics.getMeter("API");
+  const latencyHistogram = apiMeter.createHistogram("API latency", {
+    unit: "ms"
+  });
+
+  fastify.addHook("onResponse", async (request, reply) => {
+    const { method } = request;
+    const route = request.routerPath;
+    const { statusCode } = reply;
+
+    latencyHistogram.record(reply.elapsedTime, {
+      route,
+      method,
+      statusCode
+    });
+  });
+});