How to Avoid Overbilling in Firebase on the Blaze Plan

1// Navigate to: console.cloud.google.com > Billing > Budgets & alerts
2// Click: Create budget
3// Settings:
4//   Budget name: Firebase Production
5//   Projects: your-firebase-project
6//   Budget amount: $50 (or your expected monthly spend)
7//   Alert thresholds: 50%, 80%, 100%, 150%
8//   Notifications: your-team@company.com

1import { onDocumentCreated } from "firebase-functions/v2/firestore";
2import { logger } from "firebase-functions";
3
4// DANGEROUS — this creates an infinite loop:
5// export const bad = onDocumentCreated("orders/{id}", async (event) => {
6//   await event.data.ref.update({ processed: true }); // triggers itself!
7// });
8
9// SAFE — guard field prevents re-triggering:
10export const processOrder = onDocumentCreated(
11  "orders/{orderId}",
12  async (event) => {
13    if (!event.data) return;
14    const data = event.data.data();
15
16    // Guard: skip if already processed
17    if (data.processedByFunction === true) {
18      return;
19    }
20
21    await event.data.ref.update({
22      processedByFunction: true,
23      totalWithTax: data.subtotal * 1.1,
24    });
25
26    logger.info(`Processed order ${event.params.orderId}`);
27  }
28);

1import { db } from "@/lib/firebase";
2import {
3  collection, query, orderBy, limit, startAfter,
4  getCountFromServer, getDocs
5} from "firebase/firestore";
6
7// BAD: Reading all documents (could be thousands of reads)
8// const allDocs = await getDocs(collection(db, "products"));
9
10// GOOD: Paginate with limit
11async function getProducts(pageSize = 25, lastDoc?: any) {
12  let q = query(
13    collection(db, "products"),
14    orderBy("createdAt", "desc"),
15    limit(pageSize)
16  );
17
18  if (lastDoc) {
19    q = query(q, startAfter(lastDoc));
20  }
21
22  return getDocs(q);
23}
24
25// GOOD: Use aggregate queries instead of reading all docs to count
26async function getProductCount() {
27  const snapshot = await getCountFromServer(
28    collection(db, "products")
29  );
30  return snapshot.data().count; // 1 read instead of N reads
31}

1import { onRequest } from "firebase-functions/v2/https";
2import { onDocumentCreated } from "firebase-functions/v2/firestore";
3
4// User-facing API — worth keeping warm
5export const api = onRequest(
6  {
7    minInstances: 1,  // ~$3-8/mo, eliminates cold starts
8    maxInstances: 10, // Cap maximum concurrent instances
9  },
10  async (req, res) => {
11    res.json({ status: "ok" });
12  }
13);
14
15// Background trigger — cold start is acceptable
16export const onOrder = onDocumentCreated(
17  {
18    document: "orders/{orderId}",
19    // No minInstances — saves money
20    maxInstances: 5, // Still cap max to prevent runaway scaling
21  },
22  async (event) => {
23    // process order
24  }
25);

1// Navigate to: Firebase Console > your project > Usage & billing
2// Key metrics to monitor:
3//   Firestore: reads/day, writes/day, storage
4//   Cloud Functions: invocations/day, compute time
5//   Storage: bandwidth, stored data
6//   Hosting: bandwidth
7
8// For programmatic monitoring, use the Cloud Monitoring API:
9// console.cloud.google.com > Monitoring > Dashboards

1import { onMessagePublished } from "firebase-functions/v2/pubsub";
2import { logger } from "firebase-functions";
3
4// This function is triggered by Cloud Billing budget alerts
5// Set up: Billing > Budgets > Connect Pub/Sub topic
6export const budgetAlert = onMessagePublished(
7  "firebase-budget-alerts",
8  async (event) => {
9    const data = event.data.message.json;
10    const budgetAmount = data.budgetAmount;
11    const currentSpend = data.costAmount;
12    const percentUsed = (currentSpend / budgetAmount) * 100;
13
14    logger.warn(
15      `Budget alert: ${percentUsed.toFixed(1)}% used ($${currentSpend}/$${budgetAmount})`
16    );
17
18    if (percentUsed > 120) {
19      // Critical: Take emergency action
20      // Option 1: Disable billing (requires Cloud Billing API)
21      // Option 2: Set all function maxInstances to 0
22      // Option 3: Alert on-call engineer via PagerDuty/Slack
23      logger.error("CRITICAL: Budget exceeded 120%. Taking action.");
24    }
25  }
26);