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# Hello World Example

## Overview

This example demonstrates the basic concepts of Dynamo by creating a simple multi-service pipeline. It shows how to:

1. Create and connect multiple Dynamo services
2. Pass data between services using Dynamo's runtime
3. Set up a simple HTTP API endpoint
4. Deploy and interact with a Dynamo service graph

Pipeline Architecture:

```
Users/Clients (HTTP)
      │
      ▼
┌─────────────┐
│  Frontend   │  HTTP API endpoint (/generate)
└─────────────┘
      │ dynamo/runtime
      ▼
┌─────────────┐
│   Middle    │
└─────────────┘
      │ dynamo/runtime
      ▼
┌─────────────┐
│  Backend    │
└─────────────┘
```

## Component Descriptions

### Frontend Service
- Serves as the entry point for external HTTP requests
- Exposes a `/generate` HTTP API endpoint that clients can call
- Processes incoming text and passes it to the Middle service

### Middle Service
- Acts as an intermediary service in the pipeline
- Receives requests from the Frontend
- Appends "-mid" to the text and forwards it to the Backend

### Backend Service
- Functions as the final service in the pipeline
- Processes requests from the Middle service
- Appends "-back" to the text and yields tokens

## Running the Example Locally

1. Launch all three services using a single command:

```bash
cd /workspace/examples/hello_world
dynamo serve hello_world:Frontend
```

The `dynamo serve` command deploys the entire service graph, automatically handling the dependencies between Frontend, Middle, and Backend services.

2. Send request to frontend using curl:

```bash
curl -X 'POST' \
  'http://localhost:8000/generate' \
  -H 'accept: text/event-stream' \
  -H 'Content-Type: application/json' \
  -d '{
  "text": "test"
}'
```

## Deploying to and Running the Example in Kubernetes

This example can be deployed to a Kubernetes cluster using [Dynamo Cloud](../../docs/guides/dynamo_deploy/dynamo_cloud.md) and the Dynamo CLI.

### Prerequisites

You must have first followed the instructions in [deploy/cloud/helm/README.md](../../deploy/cloud/helm/README.md) to create your Dynamo cloud deployment.

### Deployment Steps

For detailed deployment instructions, please refer to the [Operator Deployment Guide](../../docs/guides/dynamo_deploy/operator_deployment.md). The following are the specific commands for the hello world example:

```bash
# Set your project root directory
export PROJECT_ROOT=$(pwd)

# Configure environment variables (see operator_deployment.md for details)
export KUBE_NS=hello-world
export DYNAMO_CLOUD=http://localhost:8080  # If using port-forward
# OR
# export DYNAMO_CLOUD=https://dynamo-cloud.nvidia.com  # If using Ingress/VirtualService

# Build the Dynamo base image (see operator_deployment.md for details)
export DYNAMO_IMAGE=<your-registry>/<your-image-name>:<your-tag>

# Build the service
cd $PROJECT_ROOT/examples/hello_world
DYNAMO_TAG=$(dynamo build hello_world:Frontend | grep "Successfully built" | awk '{ print $3 }' | sed 's/\.$//')

# Deploy to Kubernetes
export DEPLOYMENT_NAME=ci-hw
dynamo deployment create $DYNAMO_TAG -n $DEPLOYMENT_NAME
```

### Testing the Deployment

Once the deployment is complete, you can test it using:

```bash
# Find your frontend pod
export FRONTEND_POD=$(kubectl get pods -n ${KUBE_NS} | grep "${DEPLOYMENT_NAME}-frontend" | sort -k1 | tail -n1 | awk '{print $1}')

# Forward the pod's port to localhost
kubectl port-forward pod/$FRONTEND_POD 8000:8000 -n ${KUBE_NS}

# Test the API endpoint
curl -X 'POST' 'http://localhost:8000/generate' \
    -H 'accept: text/event-stream' \
    -H 'Content-Type: application/json' \
    -d '{"text": "test"}'
```

For more details on managing deployments, testing, and troubleshooting, please refer to the [Operator Deployment Guide](../../docs/guides/dynamo_deploy/operator_deployment.md).

## Expected Output

When you send the request with "test" as input, the response will show how the text flows through each service:

```
Frontend: Middle: Backend: test-mid-back
```

This demonstrates how:
1. The Frontend receives "test"
2. The Middle service adds "-mid" to create "test-mid"
3. The Backend service adds "-back" to create "test-mid-back"
