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01 - Run Locally with Docker

Before deploying to Azure Container Apps, validate your Python app in a container locally. This catches image, dependency, and port issues early.

Infrastructure Context

Service: Container Apps (Consumption) | Network: VNet integrated | VNet: ✅

This tutorial assumes a production-ready Container Apps deployment with a custom VNet, ACR with managed identity pull, and private endpoints for backend services.

flowchart TD
    INET[Internet] -->|HTTPS| CA["Container App\nConsumption\nLinux Python 3.11"]

    subgraph VNET["VNet 10.0.0.0/16"]
        subgraph ENV_SUB["Environment Subnet 10.0.0.0/23\nDelegation: Microsoft.App/environments"]
            CAE[Container Apps Environment]
            CA
        end
        subgraph PE_SUB["Private Endpoint Subnet 10.0.2.0/24"]
            PE_ACR[PE: ACR]
            PE_KV[PE: Key Vault]
            PE_ST[PE: Storage]
        end
    end

    PE_ACR --> ACR[Azure Container Registry]
    PE_KV --> KV[Key Vault]
    PE_ST --> ST[Storage Account]

    subgraph DNS[Private DNS Zones]
        DNS_ACR[privatelink.azurecr.io]
        DNS_KV[privatelink.vaultcore.azure.net]
        DNS_ST[privatelink.blob.core.windows.net]
    end

    PE_ACR -.-> DNS_ACR
    PE_KV -.-> DNS_KV
    PE_ST -.-> DNS_ST

    CA -.->|System-Assigned MI| ENTRA[Microsoft Entra ID]
    CAE --> LOG[Log Analytics]
    CA --> AI[Application Insights]

    style CA fill:#107c10,color:#fff
    style VNET fill:#E8F5E9,stroke:#4CAF50
    style DNS fill:#E3F2FD

Local Development Workflow

graph LR
    CODE[Source Code] --> BUILD[Docker Build]
    BUILD --> CONT[Container]
    CONT --> LOCAL[localhost:8000]
    LOCAL --> HEALTH[Health Check]

Prerequisites

  • Docker Engine or Docker Desktop
  • Source code with a Dockerfile

Aim for local-cloud parity

Keep local container port mapping and environment variable names aligned with your Azure deployment settings. This reduces revision failures caused by mismatched runtime assumptions.

Step-by-step

  1. Build the container image
cd app
docker build --tag aca-python-guide .

???+ example "Expected output" 

[1/6] FROM docker.io/library/python:3.11-slim
[2/6] WORKDIR /app
[3/6] COPY requirements.txt .
[4/6] RUN pip install --no-cache-dir -r requirements.txt
[5/6] COPY . .
[6/6] CMD ["gunicorn", "--bind", "0.0.0.0:8000", "--workers", "4", "--chdir", "src", "app:app"]
Successfully tagged aca-python-guide:latest

  1. Run the container locally
# Copy and customize the environment file
cp .env.example .env

docker run --publish 8000:8000 --env-file .env aca-python-guide

???+ example "Expected output" 

[2026-04-04 11:30:54 +0000] [1] [INFO] Starting gunicorn 25.3.0
[2026-04-04 11:30:54 +0000] [1] [INFO] Listening at: http://0.0.0.0:8000 (1)
[2026-04-04 11:30:54 +0000] [8] [INFO] Booting worker with pid: 8

  1. Verify health endpoint
curl http://localhost:8000/health

???+ example "Expected output" 

{"status":"healthy","timestamp":"2026-04-04T11:32:37.322216+00:00"}

You can also verify runtime metadata:

curl http://localhost:8000/info

???+ example "Expected output" 

{"containerApp":"<your-app-name>","environment":"development","name":"azure-container-apps-practical-guide","python":"3.11.15","revision":"<your-app-name>--xxxxxxx","telemetryMode":"basic","version":"1.0.0"}

  1. Inspect application logs
docker logs <container-id>

???+ example "Expected output" 

Starting application...
PORT=8000
[INFO] Starting gunicorn 25.3.0

To find the container ID: docker ps

Local parity checklist

  • Application listens on port 8000 (or your configured container port)
  • Required environment variables are present
  • /health returns HTTP 200
  • No startup exceptions in container logs

Do not commit local secret files

If you create a local .env file for testing, keep sensitive values out of source control and use placeholder values in shared examples.

Advanced Topics

  • Add local Redis or PostgreSQL via docker network and separate containers to mimic service dependencies.
  • Use OpenTelemetry locally to validate logs and traces before cloud deployment.
  • Add a Dapr sidecar for local service invocation testing.

See Also

Sources