Ambassador container pattern in Docker - Mini Project: Build & Apply

Using the Ambassador Container Pattern with Docker

📖 Scenario: You are working on a small web application that needs to connect to a database. To keep things simple and organized, you will use the Ambassador container pattern. This means you will create a separate container that acts as a helper to connect your app to the database.This pattern helps you manage connections easily and keeps your app container clean.

🎯 Goal: Build a Docker setup with two containers: one for a simple web app and one as an ambassador container that forwards requests to a database container.You will create the necessary Dockerfiles and a docker-compose.yml file to run all containers together.

📋 What You'll Learn

Create a Dockerfile for the web app container

Create a Dockerfile for the ambassador container

Create a docker-compose.yml file to define the web app, ambassador, and database containers

Configure the ambassador container to forward traffic to the database container

Run the containers and verify the web app can connect to the database through the ambassador

💡 Why This Matters

🌍 Real World

The ambassador container pattern is used in microservices and containerized applications to manage connections to external services like databases or APIs. It helps isolate connection logic and makes scaling and maintenance easier.

💼 Career

Understanding this pattern is useful for DevOps engineers and developers working with Docker and Kubernetes, as it improves application architecture and network management.

1

Create the web app Dockerfile

Create a file named Dockerfile.app with these exact contents:

FROM python:3.12-slim
WORKDIR /app
COPY app.py .
CMD ["python", "app.py"]

Docker

# Create Dockerfile.app with the specified content
# Your code here

Need a hint?

This Dockerfile sets up a Python 3.12 environment, copies the app code, and runs it.

2

Create the ambassador Dockerfile

Create a file named Dockerfile.ambassador with these exact contents:

FROM alpine/socat
CMD ["socat", "TCP-LISTEN:5432,fork,reuseaddr", "TCP:db:5432"]

Docker

FROM python:3.12-slim
WORKDIR /app
COPY app.py .
CMD ["python", "app.py"]

# Create Dockerfile.ambassador with socat forwarding
# Your code here

Need a hint?

This Dockerfile uses socat to forward TCP traffic from port 5432 to the database container named db.

3

Create the docker-compose.yml file

Create a file named docker-compose.yml with these exact services:
- app using Dockerfile.app, depends on ambassador
- ambassador using Dockerfile.ambassador, depends on db
- db using the official postgres:15 image with environment variables POSTGRES_USER=user and POSTGRES_PASSWORD=pass
Make sure ports and networks are configured so app connects to ambassador on port 5432.

Docker

FROM python:3.12-slim
WORKDIR /app
COPY app.py .
CMD ["python", "app.py"]

FROM alpine/socat
CMD ["socat", "TCP-LISTEN:5432,fork,reuseaddr", "TCP:db:5432"]

# Create docker-compose.yml with app, ambassador, and db services
# Your code here

Need a hint?

This file defines the three containers and their relationships. The app connects to the ambassador, which forwards to the db.

4

Run and verify the setup

Run docker-compose up --build in your terminal. Then, inside the app container, run python app.py to check if it connects to the database through the ambassador. The output should be:

Connected to database successfully

Docker

FROM python:3.12-slim
WORKDIR /app
COPY app.py .
CMD ["python", "app.py"]

FROM alpine/socat
CMD ["socat", "TCP-LISTEN:5432,fork,reuseaddr", "TCP:db:5432"]

version: '3.8'
services:
  db:
    image: postgres:15
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
  ambassador:
    build:
      context: .
      dockerfile: Dockerfile.ambassador
    depends_on:
      - db
  app:
    build:
      context: .
      dockerfile: Dockerfile.app
    depends_on:
      - ambassador
    environment:
      DB_HOST: ambassador
      DB_PORT: 5432

# Run docker-compose up --build and then run python app.py inside the app container
# Your code here

Need a hint?

Make sure you build and run the containers with docker-compose up --build. Then enter the app container and run python app.py.