Micro API

Micro API is a radically simplified template for building microservices with minimal boilerplate. Inspired by modern frameworks like Hono and Elysia, it focuses on pure simplicity while giving you access to the rest of @expressots/adapter-express when you need it.

What you get

Feature	Default
Three-line startup	micro(), app.get(...), app.listen(...)
Auto-response	Return a string, object, or array; the framework calls res.send / res.json for you
Auto JSON parsing	On by default
Express middleware	Drop in any RequestHandler
Studio Agent	Auto-enabled in development when the package is installed
Opt-in service mesh	CircuitBreaker, ServiceClient, ServiceDiscovery, ServiceProxy (separate imports)

Getting Started

Create a New Micro API Project

expressots new my-api --template micro

Minimal Example

import { micro } from "@expressots/adapter-express";

const app = micro();

app.get("/", () => "Hello World");

app.listen(3000);

That's it! Three lines to a working API.

Project Structure

my-api/
├── src/
│   └── api.ts              # Main entry point
├── test/
│   └── api.spec.ts
├── Dockerfile
├── docker-compose.yml
├── package.json
├── tsconfig.json
└── expressots.config.ts

Basic Usage

The entire application is defined in a single file:

// src/api.ts
import { micro } from "@expressots/adapter-express";

const app = micro();

// Return objects - automatically JSON serialized
app.get("/", () => ({
    name: "ExpressoTS Micro",
    version: "4.0.0",
    message: "Hello from ExpressoTS Micro API!",
}));

// Return strings - sent as text
app.get("/text", () => "Hello World");

// Health check
app.get("/health", () => ({
    status: "healthy",
    timestamp: new Date().toISOString(),
    uptime: process.uptime(),
}));

// Start server
app.listen(3000);

Configuration

The micro() function accepts an optional configuration object:

const app = micro({
    autoParseJson: true,    // Enable JSON parsing (default: true)
    globalPrefix: "/api",   // Prefix all routes with /api
    showBanner: true,       // Show startup banner (default: true)
});

Route Definition

HTTP Methods

app.get("/path", handler);
app.post("/path", handler);
app.put("/path", handler);
app.patch("/path", handler);
app.delete("/path", handler);

Route Parameters

app.get("/users/:id", (req) => {
    return { id: req.params.id, name: "User " + req.params.id };
});

app.get("/posts/:postId/comments/:commentId", (req) => {
    const { postId, commentId } = req.params;
    return { postId, commentId };
});

Query Parameters

app.get("/search", (req) => {
    const { q, page, limit } = req.query;
    return {
        query: q,
        page: Number(page) || 1,
        limit: Number(limit) || 10,
    };
});

Request Body

app.post("/users", (req) => {
    const { name, email } = req.body;
    return {
        id: Date.now(),
        name,
        email,
        createdAt: new Date().toISOString(),
    };
});

Middleware

Express-Style Middleware

Middleware comes before the handler (Express convention):

// Single middleware
const logRequest = (req, res, next) => {
    console.log(`${req.method} ${req.url}`);
    next();
};

app.get("/", logRequest, () => "Hello World");

// Multiple middleware
const authenticate = (req, res, next) => {
    if (!req.headers.authorization) {
        return res.status(401).json({ error: "Unauthorized" });
    }
    next();
};

const validate = (req, res, next) => {
    // validation logic
    next();
};

app.post("/users", authenticate, validate, (req) => {
    return { id: Date.now(), ...req.body };
});

Global Middleware

// Apply to all routes
app.use((req, res, next) => {
    console.log(`${new Date().toISOString()} - ${req.method} ${req.url}`);
    next();
});

// Apply to specific path prefix
app.use("/api", authenticate);

Error Handler

app.setErrorHandler((err, req, res, next) => {
    console.error(err);
    res.status(500).json({
        error: err.message,
        timestamp: new Date().toISOString(),
    });
});

// Errors thrown in handlers are caught automatically
app.get("/error", () => {
    throw new Error("Something went wrong");
});

Auto-Response

Handlers can return values directly - no need to call res.json() or res.send():

// String returns → res.send()
app.get("/text", () => "Hello World");

// Object/Array returns → res.json()
app.get("/json", () => ({ message: "Hello" }));
app.get("/array", () => [1, 2, 3]);

// Async handlers work too
app.get("/async", async () => {
    const data = await fetchData();
    return data;
});

// Still works with traditional Express style if needed
app.get("/traditional", (req, res) => {
    res.status(201).json({ created: true });
});

Advanced Features

Advanced features are imported separately - use only what you need:

import { 
    micro, 
    CircuitBreaker, 
    ServiceClient, 
    ServiceDiscovery 
} from "@expressots/adapter-express";

Circuit Breaker

Protect against cascading failures:

import { micro, CircuitBreaker } from "@expressots/adapter-express";

const app = micro();
const cb = new CircuitBreaker({
    failureThreshold: 5,    // Open after 5 failures
    successThreshold: 2,    // Close after 2 successes in half-open
    timeout: 60000,         // Reset timeout (60s)
});

app.get("/external-api", async () => {
    return await cb.execute(async () => {
        const response = await fetch("https://external-api.com/data");
        return response.json();
    });
});

// Circuit status endpoint
app.get("/circuit/status", () => cb.getStats());

Service Discovery

import { micro, ServiceDiscovery, ServiceClient } from "@expressots/adapter-express";

const app = micro();

// Initialize discovery
const discovery = new ServiceDiscovery({ type: "static" });

// Register services
discovery.registerService({
    id: "user-service-1",
    name: "user-service",
    host: "localhost",
    port: 3001,
    health: "healthy",
    lastCheck: new Date(),
});

discovery.registerService({
    id: "user-service-2",
    name: "user-service",
    host: "localhost",
    port: 3002,
    health: "healthy",
    lastCheck: new Date(),
});

// Get a healthy instance (round-robin load balancing)
app.get("/users/:id", async (req) => {
    const instance = discovery.getService("user-service");
    if (!instance) {
        throw new Error("user-service unavailable");
    }
    
    const client = new ServiceClient({
        name: "user-service",
        baseUrl: `http://${instance.host}:${instance.port}`,
        timeout: 5000,
    });
    
    return await client.get(`/users/${req.params.id}`);
});

app.listen(3000);

Service Client

Make HTTP requests to other services:

import { micro, ServiceClient } from "@expressots/adapter-express";

const app = micro();

const userClient = new ServiceClient({
    name: "user-service",
    baseUrl: "http://localhost:3001",
    timeout: 5000,
    retries: 3,
    circuitBreaker: {
        failureThreshold: 5,
        timeout: 60000,
    },
});

app.get("/users", async () => {
    return await userClient.get("/api/users");
});

app.get("/users/:id", async (req) => {
    return await userClient.get(`/api/users/${req.params.id}`);
});

app.post("/users", async (req) => {
    return await userClient.post("/api/users", req.body);
});

app.listen(3000);

Health Checks (Kubernetes Ready)

app.get("/health", () => ({
    status: "healthy",
    timestamp: new Date().toISOString(),
    uptime: process.uptime(),
}));

// Kubernetes readiness probe
app.get("/health/ready", async () => {
    const dbConnected = await checkDatabaseConnection();
    if (!dbConnected) {
        throw new Error("Database not ready");
    }
    return { status: "ready", timestamp: new Date().toISOString() };
});

// Kubernetes liveness probe
app.get("/health/live", () => ({
    status: "alive",
    timestamp: new Date().toISOString(),
}));

Serverless Deployment

AWS Lambda

import { micro, awsLambdaAdapter } from "@expressots/adapter-express";

const app = micro();

app.get("/", () => ({ message: "Hello Lambda!" }));

// Export Lambda handler
export const handler = awsLambdaAdapter(app);

serverless.yml:

service: my-micro-service
provider:
    name: aws
    runtime: nodejs20.x

functions:
    api:
        handler: dist/api.handler
        events:
            - httpApi: "*"

Body, base64, and binary content types

The Lambda adapter handles request and response bodies according to API Gateway / ALB / Function URL conventions:

Direction	Behaviour
Incoming body	If event.isBase64Encoded is true, the body is decoded with Buffer.from(body, "base64") first. When Content-Type includes application/json, the body is then JSON.parse()d (with a fallback to the raw value if parsing fails). Other types pass through as a string or Buffer.
Outgoing body (text)	Strings come back as UTF-8 with isBase64Encoded: false. app.get(...) => "<h1>...</h1>" returns text/html; => { ... } returns application/json via the response helper.
Outgoing body (binary)	If the Content-Type matches one of config.binaryContentTypes, the body is base64-encoded and isBase64Encoded: true is set. Wildcards like image/* are supported.

Configure the binary types the adapter should encode:

export const handler = awsLambdaAdapter(app, {
  binaryContentTypes: [
    "application/octet-stream",
    "application/pdf",
    "image/*",
    "video/*",
    "audio/*",
  ],
});

Make sure your API Gateway or Function URL configuration also lists these types as binary media types, otherwise the gateway will mangle the response.

Lambda-only fields

Each request handler receives the original Lambda event and context attached to req:

import type { LambdaEvent, LambdaContext } from "@expressots/adapter-express";

app.get("/", (req, res) => {
  const { event, context } = req.lambda as { event: LambdaEvent; context: LambdaContext };
  res.set("x-lambda-request-id", context.awsRequestId);
  return { region: process.env.AWS_REGION, requestId: context.awsRequestId };
});

The adapter also injects two request headers automatically:

• x-lambda-request-id: context.awsRequestId.
• x-lambda-function: context.functionName.

Cold start tips

Tip	Why
Build a single bundle (esbuild / tsup) and ship it as the function handler.	Saves ~80–150 ms of Node require() walking through node_modules.
Use micro() rather than the full AppExpress.	Skips DI container initialization. Bring DI back only if you need it.
Prefer Lambda extensions for log shipping rather than HttpTransport.	Avoids blocking the response on log network I/O.
Set binaryContentTypes precisely.	The fewer wildcards, the faster the per-request content-type lookup.

Vercel

import { micro, vercelAdapter } from "@expressots/adapter-express";

const app = micro();

app.get("/api", () => ({ message: "Hello Vercel!" }));

export default vercelAdapter(app);

Cloudflare Workers

import { micro, cloudflareAdapter } from "@expressots/adapter-express";

const app = micro();

app.get("/", () => ({ message: "Hello Workers!" }));

export default cloudflareAdapter(app);

Docker Deployment

Dockerfile

FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

FROM node:20-alpine
WORKDIR /app
RUN addgroup -g 1001 -S nodejs && adduser -S expressots -u 1001 -G nodejs
COPY --from=builder --chown=expressots:nodejs /app/node_modules ./node_modules
COPY --from=builder --chown=expressots:nodejs /app/dist ./dist
ENV NODE_ENV=production
USER expressots
EXPOSE 3000
HEALTHCHECK --interval=30s --timeout=3s CMD wget -q --spider http://localhost:3000/health || exit 1
CMD ["node", "dist/src/api.js"]

Docker Compose

version: "3.8"
services:
    app:
        build: .
        ports:
            - "3000:3000"
        environment:
            - NODE_ENV=production
            - PORT=3000
        healthcheck:
            test: ["CMD", "wget", "--spider", "-q", "http://localhost:3000/health"]
            interval: 30s
            timeout: 3s

Kubernetes Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
    name: expressots-micro
spec:
    replicas: 3
    template:
        spec:
            containers:
                - name: app
                  image: expressots-micro:latest
                  ports:
                      - containerPort: 3000
                  livenessProbe:
                      httpGet:
                          path: /health/live
                          port: 3000
                      initialDelaySeconds: 30
                      periodSeconds: 10
                  readinessProbe:
                      httpGet:
                          path: /health/ready
                          port: 3000
                      initialDelaySeconds: 5
                      periodSeconds: 5

Testing

Using Native Fetch

import "reflect-metadata";
import { micro, MicroApp } from "@expressots/adapter-express";

describe("Micro API", () => {
    let app: MicroApp;
    let baseUrl: string;

    beforeAll(async () => {
        app = micro({ showBanner: false });
        
        app.get("/", () => ({ message: "Hello" }));
        app.get("/health", () => ({ status: "healthy" }));
        
        await app.listen(0);
        const port = (app.getHttpServer().address() as { port: number }).port;
        baseUrl = `http://localhost:${port}`;
    });

    afterAll(() => {
        app.getHttpServer().close();
    });

    it("should return message", async () => {
        const response = await fetch(`${baseUrl}/`);
        const json = await response.json();
        expect(json.message).toBe("Hello");
    });

    it("should return healthy status", async () => {
        const response = await fetch(`${baseUrl}/health`);
        const json = await response.json();
        expect(json.status).toBe("healthy");
    });
});

Using createFluentRequest

import "reflect-metadata";
import { micro, MicroApp } from "@expressots/adapter-express";
import { createFluentRequest } from "@expressots/core";

describe("Micro API", () => {
    let app: MicroApp;
    let baseUrl: string;

    beforeAll(async () => {
        app = micro({ showBanner: false });
        
        app.get("/health", () => ({ status: "healthy" }));
        
        await app.listen(0);
        const port = (app.getHttpServer().address() as { port: number }).port;
        baseUrl = `http://localhost:${port}`;
    });

    it("should return healthy status", async () => {
        const request = createFluentRequest(baseUrl);
        const response = await request
            .get("/health")
            .expectStatus(200)
            .execute();
        
        expect((response.body as { status: string }).status).toBe("healthy");
    });
});

API Reference

micro(config?)

Creates a new micro API instance.

interface MicroConfig {
    autoParseJson?: boolean;  // Default: true
    globalPrefix?: string;    // Default: ""
    showBanner?: boolean;     // Default: true
}

MicroApp Methods

Method	Description
get(path, ...middleware, handler)	Register GET route
post(path, ...middleware, handler)	Register POST route
put(path, ...middleware, handler)	Register PUT route
patch(path, ...middleware, handler)	Register PATCH route
delete(path, ...middleware, handler)	Register DELETE route
use(...middleware)	Add global middleware
use(path, ...middleware)	Add path-scoped middleware
setErrorHandler(fn)	Set custom error handler
listen(port, appInfo?)	Start the server
getHttpServer()	Get HTTP server instance
getApp()	Get underlying Express app

When to Use Micro API

Use Micro API for:

• Quick prototypes and POCs
• Simple CRUD APIs
• Webhook handlers
• Serverless functions
• Microservices with few endpoints
• APIs that don't need DI

Use Full Template for:

• Complex business logic
• Multi-module applications
• Applications requiring dependency injection
• Projects with complex authorization
• Enterprise applications

Need Dependency Injection?

Micro API is designed for simplicity without DI. If you need dependency injection, decorators, and enterprise features, use the full ExpressoTS framework:

expressots new my-app --template application

Migrating from v3 createMicroAPI()

If you have legacy code using the v3-era createMicroAPI() API, here are the key changes for v4:

v3 (createMicroAPI)	v4 (micro)
createMicroAPI()	micro()
microAPI.build()	Not needed. micro() returns the app directly
app.Middleware.parse()	Auto-enabled
app.Route.get(path, handler, ...middleware)	app.get(path, ...middleware, handler)
microAPI.Container.addSingleton()	Use the full framework (@expressots/core) for DI

Quick migration example

v3 (legacy createMicroAPI):

import { createMicroAPI } from "@expressots/adapter-express";

const microAPI = createMicroAPI();
const app = microAPI.build();
app.Middleware.parse();
app.Route.get("/", (req, res) => {
    res.json({ message: "Hello" });
});
app.listen(3000);

v4 (current micro()):

import { micro } from "@expressots/adapter-express";

const app = micro();
app.get("/", () => ({ message: "Hello" }));
app.listen(3000);

createMicroAPI is removed in v4

The legacy createMicroAPI() factory is not exported from @expressots/adapter-express v4. Use micro() instead.

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Support the Project

ExpressoTS is MIT-licensed open source. See the support guide to contribute.