One of the most common questions in cloud application development is: which platform should you build on? If you want to avoid managing your own infrastructure, you will likely find yourself choosing between a Platform-as-a-Service (PaaS) option — such as Heroku or Cloud Foundry — and a serverless option such as AWS Lambda. Both abstract away the underlying hardware, but they operate quite differently. The right choice depends on the nature of your workload, your pricing preferences, and how much infrastructure control you want to retain.
Key Differences at a Glance
The following five dimensions are the most useful for comparing PaaS and serverless platforms when selecting a cloud app development environment.
1. Basic Computing Unit
With PaaS, the fundamental unit of compute is the application. You still provision instances (sometimes called dynos, containers, or cells, depending on the platform), but the platform handles patching, scaling infrastructure, and runtime maintenance. With serverless platforms like AWS Lambda, the fundamental unit is a function or task. The underlying compute instances exist, but they are completely invisible to the developer — you deploy a function, not an app.
2. Task Duration
PaaS is well suited to long-running applications — web servers, background workers, and persistent services that need to be continuously available, even when not actively processing requests. Serverless is designed for short-lived, event-driven tasks that have a clear start and end point, such as processing an uploaded file, responding to a webhook, or transforming a stream record. AWS Lambda, for example, enforces a maximum execution timeout per invocation.
3. Required Metadata and Configuration
When deploying to a PaaS, you typically need to specify the language runtime, framework, buildpack or container configuration, and resource requirements. This gives you more control but also means more upfront configuration. With serverless platforms, the required metadata is minimal. For AWS Lambda, you primarily specify an IAM execution role, the memory allocation, and a timeout value. This makes serverless faster to get started with, though it trades away some configurability.
4. Public Access and API Exposure
PaaS applications are typically exposed via a public HTTP endpoint or REST API by default — users and clients reach your app directly over the internet. AWS Lambda functions, by contrast, are not publicly accessible on their own; they are invoked from trusted internal sources such as other AWS services, event triggers, or an API Gateway sitting in front of them. Direct public internet access requires additional configuration (for example, attaching an API Gateway or an Application Load Balancer).
5. Pricing Model
With PaaS, you pay for the provisioned compute resources — instances or containers — whether or not they are actively handling traffic. This provides cost predictability for steady workloads. With serverless, you pay only for the actual executions: the number of function invocations and the compute time consumed during each invocation. For applications with spiky, unpredictable, or infrequent workloads, serverless pricing can result in significant cost savings.
Side-by-Side Comparison
| Dimension | PaaS (e.g., Heroku, Cloud Foundry) | Serverless (e.g., AWS Lambda) |
|---|---|---|
| Basic unit | Application / container instance | Function / task |
| Task duration | Long-running, persistent | Short-lived, event-driven |
| Configuration overhead | Higher (runtime, framework, resources) | Lower (IAM role, memory, timeout) |
| Public internet access | Yes, via HTTP endpoint by default | Requires API Gateway or similar |
| Pricing | Per provisioned instance/resource | Per invocation and compute duration |
| Infrastructure control | Moderate | Minimal (fully managed) |
When to Choose PaaS
- Your application needs to be continuously running (web servers, APIs with consistent traffic, long-lived background workers).
- You want some degree of control over the runtime environment, framework versions, or resource allocation.
- Your workload is predictable and you prefer a consistent, forecastable monthly spend.
- Your team is more comfortable with a traditional application deployment model.
When to Choose Serverless
- Your workload is event-driven, bursty, or highly variable — for example, processing uploads, responding to webhooks, or running scheduled jobs.
- You want to pay only for actual compute consumption rather than idle capacity.
- You want to minimise operational overhead and delegate all infrastructure management to the cloud provider.
- Individual tasks complete quickly and do not require persistent state between invocations.
Conclusion
PaaS and serverless platforms both remove the burden of managing physical or virtual servers, but they serve different use cases. Choose PaaS when you are running long-lived applications, need more infrastructure control, or prefer predictable costs. Choose serverless when your workload is short-lived and event-driven, you want to optimise for cost at low or variable traffic volumes, and you prefer a completely hands-off infrastructure experience. In practice, many production architectures use both: PaaS for the core application tier and serverless for auxiliary event-driven tasks.
Source: Originally based on an article from TechTarget (techtarget.com).