Runtimes

Apache OpenServerless (OPS) Runtimes Explained

Apache OpenServerless (OPS) is a serverless platform built on Apache OpenWhisk, designed to execute functions in a scalable, event-driven environment. OPS leverages OpenWhisk’s runtime model while extending its capabilities to support additional customization via Docker.

Overview of OPS Runtimes

A runtime in OPS is a preconfigured environment that executes a serverless function. Since serverless platforms allocate compute resources dynamically, a runtime ensures:

1. Portability – Developers can write code in different languages without managing dependencies.
2. Scalability – The system provisions and scales runtimes automatically based on demand.
3. Isolation – Each Action runs within its own dedicated runtime environment, ensuring security and consistency.
4. Resource Efficiency – The platform optimizes resource allocation by suspending inactive runtimes and reusing active ones when possible.

OPS natively supports the following runtimes:

• Python
• Node.js
• PHP

However, since OPS is built on OpenWhisk, it inherits compatibility with all OpenWhisk-supported runtimes (e.g., Java, Go) and allows users to define custom runtimes using Docker containers.

For greater flexibility, developers can also package their own runtime environments using Docker to create “black box” actions.

How OPS Runtimes Work

1. Runtime Lifecycle

OPS follows OpenWhisk’s runtime model, where each function invocation occurs in an isolated container. The lifecycle includes:

1. Initialization: A container is provisioned with the selected runtime.
2. Execution: The function code runs within the container.
3. Idle: The container is paused (but retained) for reuse (Warm Start).
4. Destroying: Idle containers are garbage-collected after some time.

2. Cold vs. Warm Starts

• Cold Start: A new container is created, increasing latency.
• Warm Start: Reuses a paused container for faster execution.

3. Runtime Composition

Each runtime includes:

• Language Interpreter/Compiler: (e.g., Python 3.12, Node.js 21).
• Action Interface: A proxy that implements a canonical protocol to integrate with the OpenWhisk platform.
• Dependencies: Preinstalled libraries (e.g., requests for Python).

Actions

Actions are the fundamental execution units in Apache OpenServerless. They are stateless functions that run on the OpenWhisk platform.

An action can be used to update a database, respond to an API call, communicate with another system, ecc.

To use a function as an action, it must conform to the following:

• The function accepts a dictionary as input and produces a dictionary as output. The input and output dictionaries are key-value pairs, where the key is a string and the value is any valid JSON value. The dictionaries are canonically represented as JSON objects when interfacing to an action via the REST API or the ops CLI.

• The function must be called main or exposed as main