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Lambda Configuration Guide

This document provides an overview of per-lambda configuration in OpenLambda, detailing trigger types, configuration options, and usage.

1. Overview

Each lambda function in OpenLambda can optionally be configured using an ol.yaml file located in the function's directory. This configuration file defines how the function is triggered and any specific execution parameters.

2. Configuration Structure

A typical ol.yaml file follows this structure:

triggers:
  http:
    - method: PUT
    - method: PATCH
  kafka:
    - bootstrap_servers:
        - "localhost:9092"
      topics:
        - "my-topic"

environment:
  MY_ENV_VAR1: "value1"
  MY_ENV_VAR2: "value2"

3. Configuration Options

a. Triggers

OpenLambda currently supports HTTP and Kafka triggers.

HTTP Triggers

Defines which HTTP methods can be used to invoke the lambda.

Example:

triggers:
  http:
    - method: GET
    - method: POST

In this case, the lambda accepts GET and POST requests.

Kafka Triggers

Defines Kafka topics the lambda should consume from. When a message arrives on a configured topic, the lambda is invoked with the message as the request body.

Example:

triggers:
  kafka:
    - bootstrap_servers:
        - "localhost:9092"
      topics:
        - "my-topic"
      auto_offset_reset: "latest"
Field Type Required Description
bootstrap_servers []string Yes List of Kafka broker addresses.
topics []string Yes Topics this lambda should consume from.
auto_offset_reset string No Where to start reading if no committed offset exists. "latest" (default) or "earliest".

A lambda can define multiple Kafka trigger entries. Each entry creates a separate consumer. For more details on Kafka triggers, including how to access Kafka metadata headers in your handler, see kafka-triggers.md.

b. Environment Variables

Defines environment variables that will be available to the lambda function at runtime.

Example:

environment:
  MY_ENV_VAR1: "production"
  MY_ENV_VAR2: "enabled"

These variables can be accessed in your lambda code using standard environment variable methods (e.g., os.environ in Python).

Note: Environment variables defined in ol.yaml are written to a .env file in the lambda's directory during execution. If your lambda already has a .env file, it will be overwritten with the values from ol.yaml.

c. Special Environment Variables

OL_ENTRY_FILE

By default, OpenLambda expects Python lambda functions to be defined in a file named f.py. You can override this by setting the OL_ENTRY_FILE environment variable to specify a different entry file.

Example:

environment:
  OL_ENTRY_FILE: "app.py"

With this configuration:

  • OpenLambda will look for app.py instead of f.py when detecting the Python runtime
  • The Python runtime will import the app module instead of f
  • For standard functions, define your handler as def f(event) in the specified file
  • For Flask/WSGI applications, define your app object in the specified file

This is useful when you want to use conventional naming (e.g., app.py for Flask applications) or integrate existing code without renaming files.

d. Sandbox Reuse

reuse_sandbox

By default, OpenLambda reuses the same sandbox across multiple invocations of a lambda function to improve performance. In some cases, such as when strict isolation is required or when avoiding state persistence between invocations, it may be desirable to create a fresh sandbox for each invocation.

This behavior can be controlled using the reuse-sandbox option.

Example:

reuse-sandbox: false

With this configuration:

  • A new sandbox is created for each lambda invocation
  • The sandbox is destroyed after the invocation completes

If reuse-sandbox is not specified, OpenLambda defaults to reusing sandboxes across invocations.

4. How to Use

a. Define Configuration

Create an ol.yaml file inside the lambda function directory with the desired configuration.

b. Deploy and Run

Ensure the OpenLambda framework is set up and execute your lambda as per the defined triggers.

5. Validations

  • HTTP triggers must specify valid HTTP methods (GET, POST, PUT, DELETE, etc.).
  • If no triggers are specified or no configuration file exists in the lambda function directory, OpenLambda will apply default behavior allowing all HTTP methods.