Serverless Functions in C++: AWS Lambda — Complete Guide

Introduction: Why C++ in Serverless?

The world of serverless computing is strongly associated with JavaScript (Node.js), Python, or Java. However, for tasks critical to performance and memory consumption, C++ becomes an ideal candidate. AWS Lambda supports C++ through the Native Runtime, allowing you to run binary files with minimal overhead.

In this article, we will break down how to write, compile, and deploy a C++ function on AWS Lambda. You will learn about the advantages of C++ in serverless architecture, environment setup, and cold start optimization.

1. Advantages of C++ over Python and Node.js

Performance and Cold Start

The main drawback of interpreted languages is the delay during cold start. A Lambda container with Python can initialize in 200-500 ms, while with C++ it takes less than 50 ms. This is critical for APIs with high latency requirements.

• Low memory consumption: A C++ binary takes ~1-3 MB compared to 20+ MB for Node.js with dependencies.
• Direct access to system resources: Working with sockets, files, and memory without a VM layer.
• Cost savings: Due to fast execution, you pay less for milliseconds of operation.

2. Setting Up the Environment for C++ on AWS Lambda

To compile C++ code for Lambda, you need to use Amazon Linux 2 (or a compatible image). The recommended approach is a Docker container with the official Lambda image.

Requirements

• CMake ≥ 3.15
• GCC 7.3+ or Clang 7+
• AWS SDK for C++ (optional, for working with S3/DynamoDB)
• Docker (for building in an environment identical to Lambda)

Basic Dockerfile for Building

FROM public.ecr.aws/lambda/provided:al2

# Install build toolsRUN yum install -y gcc-c++ cmake3 make

# Copy source filesCOPY . /codeWORKDIR /code/build

# Build static binaryRUN cmake3 .. -DCMAKE_BUILD_TYPE=Release \    -DCMAKE_CXX_FLAGS="-static-libstdc++ -static-libgcc" \    && make -j$(nproc)

# Copy result to Lambda directoryRUN cp handler /var/task/bootstrapCMD ["handler"]

3. Writing a Lambda Function in C++

Unlike Python, where the handler is a function, in C++ we create an executable file that Lambda runs as a process. Input data is passed through stdin, and the result is output to stdout.

Simple Example: JSON Processing

#include <iostream>#include <string>#include <nlohmann/json.hpp>  // Library for working with JSON

using json = nlohmann::json;

int main() {    // Read entire stdin (input JSON from Lambda)    std::string input;    std::getline(std::cin, input);

    try {        auto event = json::parse(input);

        // Extract parameters        std::string name = event.value("name", "World");        int number = event.value("number", 0);

        // Form response        json response = {            {"message", "Hello, " + name + "!"},            {"computed", number * 2},            {"language", "C++"}        };

        std::cout << response.dump() << std::endl;        return 0;    } catch (const std::exception& e) {        std::cerr << "{\\"error\\":\\"" << e.what() << "\\"}" << std::endl;        return 1;    }}

CMakeLists.txt Structure

cmake_minimum_required(VERSION 3.15)project(lambda-handler)

set(CMAKE_CXX_STANDARD 17)set(CMAKE_CXX_STANDARD_REQUIRED ON)

# Static linking for portabilityset(CMAKE_EXE_LINKER_FLAGS "-static-libstdc++ -static-libgcc")

# Include nlohmann/json (vcpkg or fetch)find_package(nlohmann_json REQUIRED)

add_executable(handler main.cpp)target_link_librar