Platform Engineer: Interview Questions(Coding)

Platform Engineer: Interview Questions(Coding).md

Platform Engineer: Interview Questions(Coding)

• Platform Engineering: Core Concepts Explained
• Platform Engineer: Interview Questions & Answers
• Platform Engineer: Interview Questions(Basics)
• Platform Engineer: Interview Questions(Coding)
• Platform Engineer: Practical Design Problems
• Platform Engineer: Interview Questions(Advanced)

🧪 Shell Scripting Hands-On Questions(Basics)

1. Write a shell script to print the top 5 processes by memory usage.

Answer:

#!/bin/bash
ps aux --sort=-%mem | head -n 6

Scorecard:

• 5 – Uses ps with sorting and formatting
• 3 – Uses top, can explain idea
• 1 – Doesn’t know ps usage

For: Junior

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2. Write a script that checks if a directory exists; if not, create it.

Answer:

#!/bin/bash
DIR="/var/log/myapp"
[ ! -d "$DIR" ] && mkdir -p "$DIR"

Scorecard:

• 5 – Uses -d, mkdir -p correctly
• 3 – Knows how to create, but misses check
• 1 – Doesn’t know test operators or paths

For: Junior

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3. Print all .log files larger than 10MB in /var/log.

Answer:

find /var/log -name "*.log" -size +10M

Scorecard:

• 5 – Uses find with -size, -name
• 3 – Uses ls -lh, less precise
• 1 – Doesn’t know how to check file sizes

For: Junior

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4. Write a script to count how many lines contain the word “error” (case-insensitive) in a file.

Answer:

#!/bin/bash
grep -i "error" "$1" | wc -l

Scorecard:

• 5 – Uses grep with -i, variable $1
• 3 – Hardcodes filename or misses flag
• 1 – Doesn’t know grep or wc

For: Junior

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5. Print all users currently logged into the system (no duplicates).

Answer:

who | awk '{print $1}' | sort | uniq

Scorecard:

• 5 – Combines who, awk, uniq correctly
• 3 – Uses who, but redundant logic
• 1 – Doesn’t understand user sessions

For: Junior

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6. Write a script to archive (tar.gz) and delete .log files older than 7 days.

Answer:

#!/bin/bash
find /var/log -name "*.log" -mtime +7 -print0 | tar -czvf logs.tar.gz --null -T -
find /var/log -name "*.log" -mtime +7 -delete

Scorecard:

• 5 – Uses find, tar, -print0 safely
• 3 – Misses null separator or delete safety
• 1 – Doesn't know archiving or find options

For: Senior

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7. Write a script to check if a port (e.g., 80) is listening on the server.

Answer:

#!/bin/bash
PORT=80
ss -tuln | grep ":$PORT"

Scorecard:

• 5 – Uses ss or netstat with filters
• 3 – Greps ps, less accurate
• 1 – Doesn’t know how to check ports

For: Senior

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8. Write a script to monitor disk usage and send an alert if any partition exceeds 80%.

Answer:

#!/bin/bash
df -h | awk '$5+0 > 80 {print "Alert: " $6 " is at " $5}'

Scorecard:

• 5 – Parses % properly with awk
• 3 – Uses df, but static or grep-only logic
• 1 – Doesn’t know df or threshold logic

For: Senior

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9. Write a script to restart a service (nginx) if it’s not running.

Answer:

#!/bin/bash
if ! pgrep nginx > /dev/null; then
  systemctl restart nginx
fi

Scorecard:

• 5 – Uses pgrep, systemctl correctly
• 3 – Uses ps, may have false positives
• 1 – Doesn’t know how to manage services

For: Senior

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10. Create a script to tail a log file in real-time, filter only “ERROR” lines and write to another file.

Answer:

#!/bin/bash
tail -F /var/log/app.log | grep --line-buffered "ERROR" >> error.log

Scorecard:

• 5 – Uses tail -F, grep, stream handling
• 3 – Misses --line-buffered or redirection
• 1 – Can’t construct pipeline

For: Senior

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🐍 Python Hands-On Coding Questions

1. Read a text file line by line and print only lines containing the word “error” (case-insensitive).

Answer:

with open('app.log') as f:
    for line in f:
        if 'error' in line.lower():
            print(line.strip())

Scorecard:

• 5 – Uses file object and string methods cleanly
• 3 – Reads file but inefficient or misses case
• 1 – Doesn’t handle file IO properly

For: Junior

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2. Write a function that takes a list of filenames and returns only those ending in .log.

Answer:

def filter_logs(files):
    return [f for f in files if f.endswith('.log')]

Scorecard:

• 5 – Uses list comprehension and string method
• 3 – Uses for-loop instead
• 1 – Fails to filter or hardcodes logic

For: Junior

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3. Parse a JSON file and print all keys at the top level.

Answer:

import json

with open('config.json') as f:
    data = json.load(f)
    print(list(data.keys()))

Scorecard:

• 5 – Uses json.load, keys()
• 3 – Knows json but manually parses
• 1 – Doesn’t know json module

For: Junior

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4. Write a script that accepts a filename as command-line argument and prints its size in bytes.

Answer:

import os, sys

filename = sys.argv[1]
print(os.path.getsize(filename))

Scorecard:

• 5 – Uses sys.argv and os.path correctly
• 3 – Hardcodes path or doesn't handle input
• 1 – Fails on argument handling or path usage

For: Junior

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5. Write a try-except block to handle file-not-found errors while reading a file.

Answer:

try:
    with open('input.txt') as f:
        print(f.read())
except FileNotFoundError:
    print("File not found.")

Scorecard:

• 5 – Uses try-except cleanly with specific error
• 3 – Catches generic exception
• 1 – Doesn’t handle errors at all

For: Junior

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6. Tail a log file and print only new lines that contain the word “critical”.

Answer:

import time

with open('app.log') as f:
    f.seek(0, 2)  # Move to end
    while True:
        line = f.readline()
        if not line:
            time.sleep(0.5)
            continue
        if 'critical' in line.lower():
            print(line.strip())

Scorecard:

• 5 – Implements tailing with filtering correctly
• 3 – Reads file but no loop or filter
• 1 – Misuses file read logic

For: Senior

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7. Parse a YAML config and print a specific key (server.port).

Answer:

import yaml

with open('config.yml') as f:
    cfg = yaml.safe_load(f)
    print(cfg['server']['port'])

Scorecard:

• 5 – Uses PyYAML correctly
• 3 – Parses YAML but hardcodes path
• 1 – Doesn’t use external libraries

For: Senior

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8. Execute a shell command from Python and capture its output.

Answer:

import subprocess

result = subprocess.run(['df', '-h'], stdout=subprocess.PIPE)
print(result.stdout.decode())

Scorecard:

• 5 – Uses subprocess.run() cleanly
• 3 – Uses os.system() (less secure)
• 1 – Doesn’t know shell execution from Python

For: Senior

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9. Create a script that reads a file and prints how many times each unique word appears.

Answer:

from collections import Counter

with open('input.txt') as f:
    words = f.read().lower().split()
    counts = Counter(words)
    print(counts)

Scorecard:

• 5 – Uses Counter, handles case
• 3 – Uses manual dict, less efficient
• 1 – Fails string split/count logic

For: Senior

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10. Monitor a directory and print a message if any .conf file is modified.

Answer: (Requires watchdog)

from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
import time

class ConfChangeHandler(FileSystemEventHandler):
    def on_modified(self, event):
        if event.src_path.endswith('.conf'):
            print(f"{event.src_path} was modified.")

observer = Observer()
observer.schedule(ConfChangeHandler(), path='.', recursive=False)
observer.start()

try:
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    observer.stop()
observer.join()

Scorecard:

• 5 – Uses observer pattern properly
• 3 – Knows polling, doesn’t use watchdog
• 1 – Doesn’t know how to monitor file changes

For: Senior

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🧩 Advanced Shell Scripting Questions (Remote/Non-basic)

1. Write a script to check SSH connectivity to a list of hosts and print which are reachable.

Answer:

#!/bin/bash
for host in "$@"; do
  if ssh -o BatchMode=yes -o ConnectTimeout=3 "$host" 'exit' 2>/dev/null; then
    echo "$host is reachable"
  else
    echo "$host is unreachable"
  fi
done

Scorecard:

• 5 – Uses ssh flags safely, loops over args
• 3 – Uses ping instead of ssh
• 1 – Doesn’t understand remote execution

For: Senior

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2. Fetch a file from a remote server using scp and verify its checksum matches a local copy.

Answer:

#!/bin/bash
remote_file="user@host:/path/to/file"
local_file="/tmp/file"

scp "$remote_file" "$local_file"

remote_sum=$(ssh user@host "sha256sum /path/to/file" | cut -d' ' -f1)
local_sum=$(sha256sum "$local_file" | cut -d' ' -f1)

[[ "$remote_sum" == "$local_sum" ]] && echo "Checksum match" || echo "Mismatch"

Scorecard:

• 5 – Uses scp, sha256sum, secure compare
• 3 – Fetches file but doesn’t verify
• 1 – Uses insecure logic or skips validation

For: Senior

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3. Write a script that logs into a remote server and restarts a service (nginx) only if it’s not running.

Answer:

#!/bin/bash
ssh user@host '
  if ! pgrep nginx > /dev/null; then
    sudo systemctl restart nginx
    echo "NGINX restarted"
  else
    echo "NGINX already running"
  fi
'

Scorecard:

• 5 – Correct remote logic with service check
• 3 – Just restarts blindly
• 1 – Can’t form remote conditional logic

For: Senior

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4. Write a script to copy a directory to multiple remote hosts in parallel using background jobs.

Answer:

#!/bin/bash
for host in "$@"; do
  scp -r ./mydir "$host:~/mydir" &
done
wait
echo "All copies done"

Scorecard:

• 5 – Uses background jobs, scp correctly
• 3 – Copies one at a time
• 1 – Doesn’t understand parallel execution

For: Senior

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5. Write a script to run a command on multiple servers and collect stdout into separate files.

Answer:

#!/bin/bash
for host in "$@"; do
  ssh "$host" "uptime" > "output_${host}.log" 2>&1 &
done
wait

Scorecard:

• 5 – Understands redirection and concurrency
• 3 – Runs serially or misuses ssh
• 1 – Outputs overwrite or fails entirely

For: Senior

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🧩 Advanced Python Scripting Questions (Remote/Tricky)

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1. Write a Python script that uses paramiko to run a command (df -h) on a remote host and print the output.

Answer:

import paramiko

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect("host", username="user", password="pass")

stdin, stdout, stderr = ssh.exec_command("df -h")
print(stdout.read().decode())

ssh.close()

Scorecard:

• 5 – Uses paramiko securely
• 3 – Runs command but no error handling
• 1 – Doesn’t know SSH in Python

For: Senior

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2. Write a script to fetch a list of servers from a JSON API and ping each.

Answer:

import json, requests, os

servers = requests.get("https://api.example.com/servers").json()
for server in servers['hosts']:
    response = os.system(f"ping -c 1 {server}")
    print(f"{server}: {'UP' if response == 0 else 'DOWN'}")

Scorecard:

• 5 – Parses API and uses system command
• 3 – Hardcodes data or misses error cases
• 1 – Can’t tie together HTTP and ping

For: Senior

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3. Write a script to download a file from S3 using boto3 and compare its size to a local copy.

Answer:

import boto3, os

s3 = boto3.client('s3')
s3.download_file('my-bucket', 'file.txt', '/tmp/file.txt')

remote_size = s3.head_object(Bucket='my-bucket', Key='file.txt')['ContentLength']
local_size = os.path.getsize('/tmp/file.txt')

print("Match" if remote_size == local_size else "Mismatch")

Scorecard:

• 5 – Uses boto3, checks metadata
• 3 – Downloads but doesn’t verify
• 1 – Doesn’t understand S3 API basics

For: Senior

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4. Create a script that SSHes into multiple servers and collects free disk space.

Answer:

import paramiko

hosts = ['host1', 'host2']
for h in hosts:
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    ssh.connect(h, username='user', password='pass')
    _, stdout, _ = ssh.exec_command('df -h /')
    print(f"{h}:\n{stdout.read().decode()}")
    ssh.close()

Scorecard:

• 5 – Loops across multiple hosts cleanly
• 3 – Static host or poor formatting
• 1 – Repeats code or handles one host only

For: Senior

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5. Use Python to upload a directory to an S3 bucket with correct MIME types.

Answer:

import boto3, mimetypes, os

s3 = boto3.client('s3')
for root, _, files in os.walk('./static'):
    for f in files:
        path = os.path.join(root, f)
        key = path[len('./static/'):]
        mime = mimetypes.guess_type(f)[0] or 'binary/octet-stream'
        s3.upload_file(path, 'my-bucket', key, ExtraArgs={'ContentType': mime})

Scorecard:

• 5 – Uses MIME types and traverses recursively
• 3 – Uploads but static types or bad keys
• 1 – Uploads one file only, wrong types

For: Senior

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