feat(store-indexer): add prometheus metrics

.changeset/afraid-eagles-learn.md

@@ -0,0 +1,5 @@
+---
+"@latticexyz/store-indexer": patch
+---
+
+Add Prometheus metrics at `/metrics` to the Postgres indexer backend and frontend, as well as the SQLite indexer.

packages/store-indexer/bin/postgres-frontend.ts

@@ -13,6 +13,7 @@ import { apiRoutes } from "../src/postgres/apiRoutes";
 import { sentry } from "../src/koa-middleware/sentry";
 import { healthcheck } from "../src/koa-middleware/healthcheck";
 import { helloWorld } from "../src/koa-middleware/helloWorld";
+import { metrics } from "../src/koa-middleware/metrics";
 
 const env = parseEnv(
   z.intersection(
@@ -34,6 +35,12 @@ if (env.SENTRY_DSN) {
 
 server.use(cors());
 server.use(healthcheck());
+server.use(
+  metrics({
+    isHealthy: () => true,
+    isReady: () => true,
+  }),
+);
 server.use(helloWorld());
 server.use(apiRoutes(database));
 

packages/store-indexer/bin/postgres-indexer.ts

@@ -96,6 +96,7 @@ if (env.HEALTHCHECK_HOST != null || env.HEALTHCHECK_PORT != null) {
   const { default: Koa } = await import("koa");
   const { default: cors } = await import("@koa/cors");
   const { healthcheck } = await import("../src/koa-middleware/healthcheck");
+  const { metrics } = await import("../src/koa-middleware/metrics");
   const { helloWorld } = await import("../src/koa-middleware/helloWorld");
 
   const server = new Koa();
@@ -106,6 +107,12 @@ if (env.HEALTHCHECK_HOST != null || env.HEALTHCHECK_PORT != null) {
       isReady: () => isCaughtUp,
     }),
   );
+  server.use(
+    metrics({
+      isHealthy: () => true,
+      isReady: () => isCaughtUp,
+    }),
+  );
   server.use(helloWorld());
 
   server.listen({ host: env.HEALTHCHECK_HOST, port: env.HEALTHCHECK_PORT });

packages/store-indexer/bin/sqlite-indexer.ts

@@ -19,6 +19,7 @@ import { healthcheck } from "../src/koa-middleware/healthcheck";
 import { helloWorld } from "../src/koa-middleware/helloWorld";
 import { apiRoutes } from "../src/sqlite/apiRoutes";
 import { sentry } from "../src/koa-middleware/sentry";
+import { metrics } from "../src/koa-middleware/metrics";
 
 const env = parseEnv(
   z.intersection(
@@ -107,6 +108,12 @@ server.use(
     isReady: () => isCaughtUp,
   }),
 );
+server.use(
+  metrics({
+    isHealthy: () => true,
+    isReady: () => isCaughtUp,
+  }),
+);
 server.use(helloWorld());
 server.use(apiRoutes(database));
 

packages/store-indexer/package.json

@@ -59,6 +59,7 @@
     "koa": "^2.14.2",
     "koa-compose": "^4.1.0",
     "postgres": "3.3.5",
+    "prom-client": "^15.1.2",
     "rxjs": "7.5.5",
     "superjson": "^1.12.4",
     "trpc-koa-adapter": "^1.1.3",

packages/store-indexer/src/koa-middleware/metrics.ts

@@ -0,0 +1,43 @@
+import { Middleware } from "koa";
+import promClient from "prom-client";
+
+type MetricsOptions = {
+  isHealthy?: () => boolean;
+  isReady?: () => boolean;
+};
+
+/**
+ * Middleware to add Prometheus metrics endpoints
+ */
+export function metrics({ isHealthy, isReady }: MetricsOptions = {}): Middleware {
+  promClient.collectDefaultMetrics();
+  if (isHealthy != null) {
+    new promClient.Gauge({
+      name: "health_status",
+      help: "Health status (0 = unhealthy, 1 = healthy)",
+      collect(): void {
+        this.set(Number(isHealthy()));
+      },
+    });
+  }
+
+  if (isReady != null) {
+    new promClient.Gauge({
+      name: "readiness_status",
+      help: "Readiness status (whether the service is ready to receive requests, 0 = not ready, 1 = ready)",
+      collect(): void {
+        this.set(Number(isReady()));
+      },
+    });
+  }
+
+  return async function metricsMiddleware(ctx, next): Promise<void> {
+    if (ctx.path === "/metrics") {
+      ctx.status = 200;
+      ctx.body = await promClient.register.metrics();
+      return;
+    }
+
+    await next();
+  };
+}