Serverless functions (Function as a Service, or FaaS) are event-triggered code snippets that run without server management. You write a function, deploy it, and the cloud provider handles scaling, availability, and infrastructure. Common platforms include AWS Lambda, Google Cloud Functions, Azure Functions, and Vercel Functions. This guide covers when to use serverless functions, their limitations, and alternatives for backend development.

What Are Serverless Functions?

Serverless functions, or Function as a Service (FaaS), allow developers to execute code in response to events without managing underlying servers. They are stateless, event-driven, and automatically scale with demand.

When and Why to Use Serverless Functions?

When:

• Rapid Prototyping: Quick deployment without server setup.
• Event-Driven Scenarios: Such as reacting to file uploads, database changes, etc.
• Variable Workloads: Managing spikes or drops in traffic.
• Microservices Architecture: Building independent, scalable services.

Why:

• Cost Efficiency: Pay only for execution time.
• Ease of Management: No need to handle servers.
• Automatic Scaling: Scales with demand.
• Rapid Development: Focus on coding, not infrastructure.

How Do Serverless Functions Change Application Design?

Using serverless functions often requires a shift in application design:

• State Management: Being stateless, serverless functions require different strategies for managing state.
• Shorter Running Time: They are designed for short, reactive tasks. This means it is difficult to design for business logic requiring long-running tasks.
• Event-Driven Architecture: The architecture revolves around reacting to events.
• Integration with Other Services: Often used with other cloud services for full functionality.

Pros and Cons on Serverless Functions

Pros:

• Cost-Effective: Pay for usage.
• Rapid Deployment: Less focus on infrastructure.
• Scalability: Automatic scaling.
• Integration: Easy integration with other cloud services.

Cons:

• Cold Starts: Initial latency in execution.
• State Management: Challenges in managing state.
• Limited Execution Time: Not suitable for long-running processes.
• Vendor Lock-in: Potential reliance on specific cloud providers.

What Are Step Functions?

Step functions coordinate the components of distributed applications and microservices. They provide a way to sequence serverless functions and other services, creating visual workflows to build applications quickly.

What are Lambda Functions?

Serverless Lambda functions (an AWS offering) provide an environment to run code in various languages in reaction to triggers. They offer all the benefits of serverless architecture, enabling scalable, event-driven, cost-effective applications.

Limitations and Alternatives

While serverless functions work well for simple, event-driven tasks, they have significant limitations for backend applications:

Limitation	Impact
Cold starts	100ms-2s latency spikes on first invocation
Execution timeout	AWS Lambda: 15 min max; Vercel: 10s-300s depending on plan
Connection limits	Database connections are difficult to pool
No WebSockets	Long-lived connections require workarounds
State management	Functions are stateless by design

For backend APIs that need persistent connections, background jobs, or low latency, consider alternatives like containers (Fargate, Cloud Run) or dedicated compute.

Encore: Flexible Deployment Without Lock-in

Encore provides a development platform that lets you write backend code once and deploy to the most appropriate infrastructure:

• Serverless when it makes sense: Cloud Run, Fargate for cost-effective scaling
• Containers when you need control: Kubernetes, ECS for persistent workloads
• Same code, any target: No code changes required when switching deployment models

Encore also includes built-in primitives that eliminate common serverless workarounds:

import { CronJob } from "encore.dev/cron";
import { SQLDatabase } from "encore.dev/storage/sqldb";

// Cron jobs run reliably without timeout limits
new CronJob("daily-report", {
  schedule: "0 9 * * *",
  endpoint: generateDailyReport,
});

// Database connections are pooled automatically
const db = new SQLDatabase("app", { migrations: "./migrations" });

For teams using Vercel for their frontend but needing a robust backend, see Encore vs Vercel for Backends.

Conclusion

Serverless functions mark a significant advancement in cloud computing, enabling scalable, event-driven applications with cost efficiency. While there are notable pros and cons, understanding your specific needs and constraints will guide the most effective use of serverless functions. Integrating technologies like Encore can provide an even more flexible, adaptable, and future-proof approach to modern development.