4.18 Real-World DevOps Examples

Seeing correct syntax structure in realistic scripts reinforces the rules covered across this chapter better than isolated snippets — here’s how the pieces come together in practice.

Configuration Scripts

A typical config module: constants at the top, dictionary literal for structured settings — direct application of 4.9 Constants and 4.10 Literals.

# config.py
MAX_RETRIES = 3
TIMEOUT_SECONDS = 30

DATABASE = {
    "host": "localhost",
    "port": 5432,
    "name": "prod_db",
}

Automation Scripts

A file-cleanup script showing imports, a function block, and the entry-point guard together — the full layout from 4.2 Structure of a Python Program in action.

import os

def remove_old_logs(folder, days=7):
    for filename in os.listdir(folder):
        print(f"Checking {filename}")

if __name__ == "__main__":
    remove_old_logs("/var/log/app")

Log Processing Script Structure

A minimal but complete log-scanning script — notice the consistent indentation nesting a for loop inside a with block.

def count_errors(log_path):
    error_count = 0
    with open(log_path) as f:
        for line in f:
            if "ERROR" in line:
                error_count += 1
    return error_count

AWS Script Layout

A boto3-based script following the same import → constants → function → entry-point pattern used throughout this chapter.

import boto3

REGION = "us-east-1"

def list_running_instances():
    ec2 = boto3.client("ec2", region_name=REGION)
    return ec2.describe_instances()

if __name__ == "__main__":
    list_running_instances()

Quick Interview Answer

“Real DevOps scripts follow the same layout as any other Python file: imports, then constants (a config dict, an AWS region, retry counts), then function definitions, then an if __name__ == '__main__': guard. Whether it’s cleaning up log files with os, scanning a log for errors with with open(...), or listing EC2 instances with boto3, the underlying syntax rules — indentation, colons, blocks — never change.”

Common Mistakes

• Hardcoding values like AWS region or file paths directly inside functions instead of pulling them from module-level constants, making the script harder to reconfigure.
• Forgetting the with statement when opening a file, leaving it to rely on garbage collection to eventually close the file handle.