Hi all, this blog consists of quick small concepts to revise/braintune the DevOps concepts. This blog can also be used for interview purposes where I would append with new content on regular basis.

1.⏰𝗦𝗲𝘁/𝗖𝗵𝗮𝗻𝗴𝗲 𝗧𝗶𝗺𝗲 𝗭𝗼𝗻𝗲 𝗼𝗳 𝗮 𝗟𝗶𝗻𝘂𝘅 𝗠𝗮𝗰𝗵𝗶𝗻𝗲 ⏰

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: timedatectl
📝 shows the current timezone with additional details related to datetime

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: timedatectl list-timezones
📝 used to list all the available timezones

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: timedatectl set-timezone Asia/Kolkata
📝 used to set the timezone Asia/Kolkata

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2.💻 𝗟𝗶𝗺𝗶𝘁 𝗖𝗣𝗨 & 𝗠𝗲𝗺𝗼𝗿𝘆 𝗼𝗳 𝗗𝗼𝗰𝗸𝗲𝗿 𝗖𝗼𝗻𝘁𝗮𝗶𝗻𝗲𝗿 ⚙️

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱:
💻 docker run -dt --name vish_cont --memory 100m --cpus 0.5 busybox
📝📝starts a container named 𝘃𝗶𝘀𝗵_𝗰𝗼𝗻𝘁 with 𝟭𝟬𝟬 𝗠𝗕 of memory and 𝟬.𝟱 𝗰𝗼𝗿𝗲𝘀 of CPU

🔹𝗩𝗮𝗹𝗶𝗱𝗮𝘁𝗶𝗼𝗻 𝗼𝗳 𝗠𝗲𝗺𝗼𝗿𝘆:
💻 docker stats vish_cont
📝📝 shows the stats of the running container

💻 docker exec -it vish_cont sh
📝📝 gets into the running container named vish_cont

💻 cat /sys/fs/cgroup/memory.max
📝📝 shows the output max memory in bytes
📝📝📝 divide the number by 1024*1024 to get in MB

🔹𝗩𝗮𝗹𝗶𝗱𝗮𝘁𝗶𝗼𝗻 𝗼𝗳 𝗖𝗣𝗨
💻 docker exec -it vish_cont sh
📝📝 gets into the running container named vish_cont

💻 cat /sys/fs/cgroup/cpu.max
📝📝 shows the output of the number of cores used
📝📝📝 divide the output first number with the second to get the number of cpu cores

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3.🕒 𝗖𝗿𝗼𝗻𝘁𝗮𝗯 & 𝗖𝗿𝗼𝗻 𝗘𝘅𝗽𝗿𝗲𝘀𝘀𝗶𝗼𝗻🕒

🕒 𝗖𝗿𝗼𝗻𝘁𝗮𝗯 🕒
📝📝 crontab aka 𝑪𝒓𝒐𝒏 𝑻𝒂𝒃𝒍𝒆 is a configuration file to schedule & automate tasks

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: crontab -l
📝📝 used to list the available cron jobs scheduled

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: crontab -e
📝📝 used to list the available cron jobs scheduled

🕒 𝗖𝗿𝗼𝗻 𝗘𝘅𝗽𝗿𝗲𝘀𝘀𝗶𝗼𝗻 🕒 - Refer post picture to understand the expression
📝📝 visit the website to generate cron expression - https://crontab.guru/

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4.🔍 𝗤𝘂𝗶𝗰𝗸𝗹𝘆 𝗦𝗲𝗮𝗿𝗰𝗵 𝗙𝗶𝗹𝗲𝘀/𝗙𝗼𝗹𝗱𝗲𝗿𝘀 𝘂𝘀𝗶𝗻𝗴 𝗟𝗼𝗰𝗮𝘁𝗲 𝗖𝗼𝗺𝗺𝗮𝗻𝗱 🔍

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: sudo apt install plocate
📝📝 install the plocate on debian based systems

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: updatedb
📝📝 updates the database that locate uses
📝📝📝 locate is faster because it uses this prebuilt database instead of filesystem

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: locate <file/folder pattern>
📝📝 used to quickly find location of files and directories
📝📝📝 returns the absolute path of the file/folder mentioned
📝📝📝📝 example: locate add.txt, locate *.tar

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: locate -i <file/folder pattern>
📝📝 case insenstive search

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5.🔢 𝗧𝗲𝗿𝗿𝗮𝗳𝗼𝗿𝗺 𝗩𝗮𝗿𝗶𝗮𝗯𝗹𝗲 𝗢𝗿𝗱𝗲𝗿 𝗼𝗳 𝗣𝗿𝗲𝗰𝗲𝗱𝗲𝗻𝗰𝗲 🔢

Terraform variables take the following precedence:
🔹 Environment Variables
📝📝 terraform environment variables starts with TF_VAR_<variableName>

🔹 Variable Defaults
📝📝 variable blocks consisting the default value

🔹 Terraform tfvars (terraform.tfvars)
📝📝 seperate file named terraform.tfvars with variables defined

🔹 CLI (using -var and -var-file)
📝📝 passing variable name (-var=<varName=varValue>)
📝📝 passing variable filename (-var-file=<fileNmae>)

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6.⌨️ 𝗠𝘆 𝗳𝗿𝗲𝗾𝘂𝗲𝗻𝘁𝗹𝘆 𝘂𝘀𝗲𝗱 𝘃𝗶 𝗲𝗱𝗶𝘁𝗼𝗿 𝗸𝗲𝘆𝗯𝗼𝗮𝗿𝗱 𝘀𝗵𝗼𝗿𝘁𝗰𝘂𝘁𝘀 ⌨️

📝 𝗖𝘂𝗿𝘀𝗼𝗿 𝗢𝗽𝗲𝗿𝗮𝘁𝗶𝗼𝗻𝘀
🔹Move cursor to start of the line - "𝗴𝗴"
🔹Move cursor to end of the line - "𝘀𝗵𝗶𝗳𝘁 + 𝗴"

📝 𝗙𝗶𝗻𝗱 & 𝗥𝗲𝗽𝗹𝗮𝗰𝗲 𝗢𝗽𝗲𝗿𝗮𝘁𝗶𝗼𝗻𝘀
🔹Search for a pattern & move cursor to it - "/<𝘀𝗲𝗮𝗿𝗰𝗵𝗣𝗮𝘁𝘁𝗲𝗿𝗻>"
🔹Find & replace old text to new text - ":%𝘀/𝗼𝗹𝗱𝗧𝗲𝘅𝘁/𝗻𝗲𝘄𝗧𝗲𝘅𝘁"

📝 𝗗𝗲𝗹𝗲𝘁𝗲 𝗢𝗽𝗲𝗿𝗮𝘁𝗶𝗼𝗻𝘀
🔹Delete the current line - "𝗱𝗱"
🔹Delete all contents of file - "𝗴𝗴 𝗱𝗚"
🔹Delete current line & next desired number of lines - "𝗱<𝗻𝘂𝗺𝗯𝗲𝗿𝗢𝗳𝗟𝗶𝗻𝗲𝘀>"

📝 𝗠𝗶𝘀𝗰 𝗢𝗽𝗲𝗿𝗮𝘁𝗶𝗼𝗻𝘀
🔹Undo the operation - "𝘂"
🔹Set the line numbers - ":𝘀𝗲𝘁 𝗻𝘂"

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7.🛠️ 𝗧𝗿𝗶𝗴𝗴𝗲𝗿 𝗖𝗹𝗼𝘂𝗱𝗪𝗮𝘁𝗰𝗵 𝗔𝗹𝗮𝗿𝗺 𝗳𝗼𝗿 𝘁𝗲𝘀𝘁𝗶𝗻𝗴 🛠️

🔹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱: Using AWS CLI
📝📝 aws cloudwatch set-alarm-state --alarm-name "VishCPU_70" --state-value ALARM --state-reason "Testing Vish Alarm"
📝📝📝 This helps in quickly testing the alarm when the threshold is not reached.
📝📝📝📝 Sets the VishCPU_70 alarm to ALARM state and can send notifications based on the alarm configured.

𝗘𝘅𝘁𝗿𝗮𝘀:
𝗔𝗹𝗮𝗿𝗺 𝗦𝘁𝗮𝘁𝗲𝘀:
𝗢𝗞 𝗦𝘁𝗮𝘁𝗲 - alarm is within the threshold defined
𝗔𝗟𝗔𝗥𝗠 𝗦𝘁𝗮𝘁𝗲 - alarm crossed the threshold defined
𝗜𝗡𝗦𝗨𝗙𝗙𝗜𝗖𝗜𝗘𝗡𝗧_𝗗𝗔𝗧𝗔 𝗦𝘁𝗮𝘁𝗲 - Dont have much data to trigger the alarm

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