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Add monolith-to-microservices GKE tutorial sample (#1663)
* Add monolith-to-microservices GKE tutorial sample * Insert license headers into Python, JSON, HTML and YAML files * Add license header to start_services.sh * Addressed PR feedback: fixed CSS license headers, updated Python version, added tutorial link to README --------- Co-authored-by: Olivier Bourgeois <3271352+bourgeoisor@users.noreply.github.com>
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‎.github/workflows/quickstarts-monolith-to-microservices-ci.yml ‎

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name: quickstarts-monolith-to-microservices-ci
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on:
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push:
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branches:
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- main
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paths:
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- '.github/workflows/quickstarts-monolith-to-microservices-ci.yml'
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- 'quickstarts/monolith-to-microservices/**'
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pull_request:
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paths:
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- '.github/workflows/quickstarts-monolith-to-microservices-ci.yml'
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- 'quickstarts/monolith-to-microservices/**'
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jobs:
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build:
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runs-on: ubuntu-22.04
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steps:
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- uses: actions/checkout@v4
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- name: Build home-app container
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run: |
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docker build -t home-app quickstarts/monolith-to-microservices/containerized/home_app
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- name: Build book-details-app container
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run: |
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docker build -t book-details-app quickstarts/monolith-to-microservices/containerized/book_details_app
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- name: Build book-reviews-app container
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run: |
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docker build -t book-reviews-app quickstarts/monolith-to-microservices/containerized/book_reviews_app
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- name: Build images-app container
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run: |
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docker build -t images-app quickstarts/monolith-to-microservices/containerized/images_app

‎quickstarts/monolith-to-microservices/README.md‎

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# Monolith to Microservices on GKE
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This code accompanies a tutorial series (https://cloud.google.com/kubernetes-engine/docs/learn/cymbal-books/overview) that shows you how to take a monolith, modularize the code, containerize each module, and deploy the container images to a Google Kubernetes Engine (GKE) cluster.
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## Contents
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This sample contains three versions of the Cymbal Books app:
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- `monolith/`: The original monolithic Flask app
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- `modular/`: A modular version with separate Flask services communicating over HTTP
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- `containerized/`: Dockerized services and a Kubernetes manifest for GKE deployment
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## Architecture
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The monolith is incrementally broken into four modules:
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- **Home app**: Serves the main page and coordinates other services
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- **Book details app**: Provides information about books
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- **Book reviews app**: Returns user reviews for each book
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- **Images app**: Serves book cover images
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Each service is containerized and deployed into its own Pod. A corresponding Kubernetes Service enables internal communication.
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## Setup
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### Prerequisites for the containerize part of the tutorial
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- A Google Cloud project with billing enabled
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---
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### Step 1: Build Container Images
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From the `containerized/` directory:
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```bash
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docker build -t home-app ./home_app
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docker build -t book-details-app ./book_details_app
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docker build -t book-reviews-app ./book_reviews_app
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docker build -t images-app ./images_app
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```
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### Step 2: Push to Artifact Registry
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Replace placeholders with your own values:
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```bash
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docker tag home-app REGION-docker.pkg.dev/PROJECT_ID/REPO_NAME/home-app
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docker push REGION-docker.pkg.dev/PROJECT_ID/REPO_NAME/home-app
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# Repeat for other images...
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```
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### Step 3: Update Kubernetes Manifest
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Edit kubernetes-manifest.yaml and replace image paths with your Artifact Registry URLs:
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```bash
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# Example
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image: us-west1-docker.pkg.dev/my-project/my-repo/home-app:v1
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```
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### Step 4: Deploy to GKE
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```bash
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kubectl apply -f kubernetes-manifest.yaml
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```
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### Step 5: Access the App
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After deployment, find the external IP of the home service:
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```bash
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kubectl get services
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```
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Then open the app in your browser:
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```bash
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http://<EXTERNAL-IP>
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```
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## License
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Apache 2.0 © Google LLC
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‎quickstarts/monolith-to-microservices/containerized/book_details_app/Dockerfile‎

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# Dockerfile for book_details_app
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FROM python:3.13-alpine
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WORKDIR /app
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COPY requirements.txt .
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RUN pip install --no-cache-dir -r requirements.txt
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COPY book_details_app.py .
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COPY data/ ./data/
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CMD ["python", "book_details_app.py"]

‎quickstarts/monolith-to-microservices/containerized/book_details_app/book_details_app.py‎

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# Copyright 2025 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# https://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from flask import Flask, jsonify
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import json
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import os
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app = Flask(__name__)
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DATA_DIR = 'data'
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def read_json_file(filename):
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with open(os.path.join(DATA_DIR, filename), 'r') as file:
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return json.load(file)
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@app.route('/books')
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def get_books():
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books = [read_json_file(f'book-{i}.json') for i in range(1, 4)]
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return jsonify(books)
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@app.route('/book/<int:book_id>')
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def get_book(book_id):
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book = read_json_file(f'book-{book_id}.json')
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return jsonify(book)
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if __name__ == '__main__':
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app.run(host='0.0.0.0', port=8080)

‎quickstarts/monolith-to-microservices/containerized/book_details_app/data/book-1.json‎

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{
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"id": 1,
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"title": "Zephyr's Timepiece",
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"author": "Aria Clockwork",
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"year": 2023,
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"description": "In a world where time is a tangible substance, a young clockmaker discovers she can manipulate the fabric of time itself, leading to unforeseen consequences in her steampunk-inspired city.",
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"image_url": "zephyrs_timepiece.jpg"
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}

‎quickstarts/monolith-to-microservices/containerized/book_details_app/data/book-2.json‎

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{
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"id": 2,
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"title": "Fungi Frontier",
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"author": "Myco Sporesworth",
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"year": 2024,
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"description": "A mycologist leads an expedition to explore a newly discovered underground ecosystem entirely composed of sentient fungi, challenging the team's understanding of consciousness and life itself.",
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"image_url": "fungi_frontier.jpg"
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}

‎quickstarts/monolith-to-microservices/containerized/book_details_app/data/book-3.json‎

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{
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"id": 3,
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"title": "Melodic Mechanics",
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"author": "Harmony Gearsmith",
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"year": 2025,
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"description": "In a city where every machine runs on music, a tone-deaf engineer must find a way to keep the city's vital systems running when a mysterious silence begins to spread.",
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"image_url": "melodic_mechanics.jpg"
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}

‎quickstarts/monolith-to-microservices/containerized/book_details_app/requirements.txt‎

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Flask==2.3.2
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Werkzeug==2.3.4
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Jinja2==3.1.2
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requests==2.30.0

‎quickstarts/monolith-to-microservices/containerized/book_reviews_app/Dockerfile‎

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# Dockerfile for book_reviews_app
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FROM python:3.13-alpine
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WORKDIR /app
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COPY requirements.txt .
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RUN pip install --no-cache-dir -r requirements.txt
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COPY book_reviews_app.py .
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COPY data/ ./data/
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CMD ["python", "book_reviews_app.py"]

‎quickstarts/monolith-to-microservices/containerized/book_reviews_app/book_reviews_app.py‎

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# Copyright 2025 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# https://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from flask import Flask, jsonify
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import json
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import os
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app = Flask(__name__)
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DATA_DIR = 'data'
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def read_json_file(filename):
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with open(os.path.join(DATA_DIR, filename), 'r') as file:
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return json.load(file)
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@app.route('/book/<int:book_id>/reviews')
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def get_reviews(book_id):
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reviews = read_json_file(f'reviews-{book_id}.json')
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return jsonify(reviews)
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if __name__ == '__main__':
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app.run(host='0.0.0.0', port=8080)

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