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Session 5: Custom AWS Lambda Runtimes with RIC

A visual and practical guide for understanding and deploying AWS Lambda custom runtimes using the🔙 CDK Commands 🛠️ | 🏠 Index | 🔜 Practical Workshop: API Gateway & Lambda 🔥

🔁 Ready to try this live? Let's build your first custom Lambda runtime now!Runtime Interface Client (RIC)**. Tailored for engineers who want full control over Lambda behavior in container images.

🔍 Workshop Goal

Understand and deploy a custom Lambda runtime using RIC, and grasp its role in the event processing lifecycle.

✅ Key takeaways:

  • Why RIC is essential
  • How it interacts with AWS Lambda Runtime API
  • Build and deploy a working Lambda with API Gateway using RIC

🧱 Prerequisites / Setup

Before the session:

  • Docker installed
  • AWS CLI configured
  • Basic understanding of AWS Lambda + API Gateway
  • Familiarity with Python or similar language
  • Node.js or .NET users: good to compare with managed runtimes

⚙️ Agenda & Phases

  1. 🧠 Concept: What is RIC and Why It Matters
  2. 🔧 Build a custom Python runtime
  3. 🚀 Deploy to AWS Lambda
  4. 🧪 Test via API Gateway
  5. 🧩 Deep dive into internal Lambda event flow

🧪 Hands-On: Custom Python Lambda with RIC

📁 Directory structure

/custom-lambda
├── app/
│   └── handler.py
├── requirements.txt
└── Dockerfile

🐳 Dockerfile

FROM python:3.9

COPY app/ /var/task/
RUN pip install --target /var/task awslambdaric
RUN pip install --no-cache-dir -r /var/task/requirements.txt --target /var/task

WORKDIR /var/task
ENTRYPOINT ["/usr/local/bin/python", "-m", "awslambdaric"]
CMD ["app.handler"]

💡 What RIC Actually Does

RIC = Runtime Interface Client → acts as a layer between AWS Lambda's infra and your function code.

📥 It

  • Polls the Lambda Runtime API for new events
  • Passes the event to your function handler
  • Sends the result (or error) back to Lambda

📊 Flowchart: Internal Event Lifecycle

flowchart TD
    A[AWS Lambda Infra] -->|Invoke| B[Runtime API]
    B -->|Get next invocation| C["Runtime Interface Client (RIC)"]
    C -->|Call handler| D["Our Code (Handler)"]
    D -->|Return result| C
    C -->|Send response| B
    B --> A

    %% Style AWS components (orange with white text)
    style A fill:#f9b66d,stroke:#e58e26,stroke-width:2px,color:white
    style B fill:#f9b66d,stroke:#e58e26,stroke-width:2px,color:white
    style C fill:#f9b66d,stroke:#e58e26,stroke-width:2px,color:white
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🔁 Sequence Diagram: Example Request Handling

%%{init: {"themeVariables": {
  "actorBorder": "#e58e26",
  "actorBkg": "#f9b66d",
  "actorTextColor": "white"
}}}%%
sequenceDiagram
    participant AWS_Lambda as AWS Lambda
    participant Runtime_API as Runtime API
    actor Your_Code as Your Code

    AWS_Lambda->>Runtime_API: GET /invocation/next
    Runtime_API->>Your_Code: handler(event)
    Your_Code-->>Runtime_API: result
    Runtime_API->>AWS_Lambda: POST /invocation/<id>/response
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🧠 Summary: .NET vs Python

Language Needs RIC? Why?
.NET (Amazon.Lambda.AspNetCoreServer.Hosting) ❌ Already implements Runtime API
Python in custom container ✅ Needs RIC to connect with Lambda Runtime API

📈 Expected Outcomes

After this session you’ll be able to:

  • Build your own custom Lambda runtime from scratch
  • Understand the role of RIC
  • Use RIC to handle real events behind API Gateway
  • Debug your container using local RIC-based logic

❓FAQs / Common Issues

  • Do I need RIC if I use AWS base images? → ❌ No. It's already pre-installed.

  • Why doesn’t .NET need RIC? → Because the hosting library already speaks the Runtime API.

  • What happens if I forget to install RIC? → Your Lambda won't start. It’ll hang waiting for an entrypoint or fail with timeout.

🔙 CDK Commands 🛠️ | 🏠 Index | 🔜 Deploy API Gateway Lambda 🚀

🔁 Ready to try this live? Let’s build your first custom Lambda runtime now!