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Datadog Agent Setup for Python App on EC2

Purpose: Install and configure the Datadog Agent to collect host metrics and APM traces from a Python FastAPI application. This setup works for autoscaling environments and ensures host metrics and traces are reported automatically.

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1. Prerequisites

  • EC2 instance with Python 3.8+ and a virtual environment (venv) installed.
  • Datadog account with API key.
  • Security group allowing outbound HTTPS (port 443) for agent reporting.
  • Python app installed at /home/<user>/<app-name> (example uses example-app).

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2. Install Datadog Agent

  1. Set environment variables for your Datadog API key, site, and environment:
export DD_API_KEY=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
export DD_SITE="datadoghq.com"   # Use datadoghq.eu for EU, datadoghq.in for India
export DD_ENV=prod
  1. Install Datadog Agent v7:
bash -c "$(curl -L https://install.datadoghq.com/scripts/install_script_agent7.sh)"
  1. Verify installation:
sudo systemctl status datadog-agent
sudo datadog-agent status

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3. Configure Datadog Agent

  1. Edit the main configuration file:
sudo nano /etc/datadog-agent/datadog.yaml
Ensure the following entries exist: 
api_key: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
site: datadoghq.com
tags:
  - env:prod

apm_config:
  enabled: true
  env: prod
  1. Restart the agent:
sudo systemctl restart datadog-agent
  1. Verify APM listener:
sudo datadog-agent status | grep -A10 "APM Agent"
  • Should show listener running on 127.0.0.1:8126.

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4. Python Application Setup (example-app)

Directory structure example: 
/home/ec2-user/example-app/
├── venv/
├── main.py
├── requirements.txt
  1. Activate virtual environment and install dependencies:
source /home/ec2-user/example-app/venv/bin/activate
pip install ddtrace uvicorn fastapi

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5. Create Systemd Service for Python App

  1. Create the unit file /etc/systemd/system/example-app.service:
[Unit]
Description=Example Python FastAPI Application
After=network.target

[Service]
User=root
Group=root
WorkingDirectory=/home/ec2-user/example-app
Environment=DD_AGENT_HOST=127.0.0.1
Environment=DD_SERVICE=example-app
Environment=DD_ENV=prod
Environment=DD_VERSION=1.0.0
Environment=DD_TRACE_REMOVE_INTEGRATION_SERVICE_NAMES=true
ExecStart=/home/ec2-user/example-app/venv/bin/ddtrace-run /home/ec2-user/example-app/venv/bin/uvicorn main:app --host 0.0.0.0 --port 8000
Restart=always
RestartSec=5
StandardOutput=journal
StandardError=journal

[Install]
WantedBy=multi-user.target
  1. Enable and start the service:
sudo systemctl daemon-reload
sudo systemctl enable example-app
sudo systemctl start example-app
sudo journalctl -u example-app -f
ddtrace-run ensures traces from the Python app are sent to the local Datadog Agent. Logs are captured in the systemd journal and can be viewed using journalctl.

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6. Verification

  1. Host Metrics:
    • Go to Datadog Dashboard → Host Metrics
    • Verify CPU, memory, disk, and network metrics from the EC2 instance.
  2. APM Traces:
    • Go to Datadog APM → Tracing Dashboard
    • Requests to your FastAPI app should appear automatically with traces.
  3. Agent Status: 
    sudo datadog-agent status
    Ensure:
    • Forwarder API key is valid.
    • Core checks (system.cpu, system.mem, etc.) show OK.
    • APM Agent listener is running.

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✅ References