100 Days of DevOps, Day 1: Linux User Management and AWS Key Pairs

Doing the work and being able to explain the work are two different skills. I've had the first one for 8 years. I'm building the second one now. I'm a Cloud Platform Engineer. AWS, Kubernetes, Terraform, Linux. Regulated environments, healthcare, production systems. Real experience. Almost zero public documentation of it. That's the gap I'm closing, starting from Day 1. The platform is KodeKloud. Each session gives you tasks across multiple tools. I'm posting the Linux and AWS tasks here. Here's what I built and what actually matters about each one. Task 1 (Linux): Create a User with a Non-Interactive Shell The task was to create a system user that can own processes but cannot log in interactively. This is what you do for service accounts. bash ssh user@hostname sudo su - useradd username -s /sbin/nologin cat /etc/passwd | grep username The /sbin/nologin shell is the important part. The user exists in the system, can own files and run processes, but cannot open a shell session. You verify by checking /etc/passwd because the last field in each line is the assigned shell. I've been doing this in production environments for years. I still verify every time. Not because I'm unsure. Because in a regulated environment, you don't assume, you confirm. Task 2 (AWS): Create an EC2 Key Pair via CLI aws ec2 create-key-pair \ --key-name my-key-pair \ --key-type rsa \ --key-format pem \ --query "KeyMaterial" \ --output text > my-key-pair.pem aws ec2 describe-key-pairs --key-names my-key-pair The private key is returned exactly once at creation. AWS does not store it. If you lose it, you generate a new one and replace it everywhere it was used. I've seen this cause real problems in production environments where the key wasn't backed up properly. Always run chmod 400 my-key-pair.pem after saving it. SSH will refuse to use a key file with open permissions. It won't tell you that's the reason straight away. What Day 1 Taught Me That 8 Years Didn't Nothing here was technically new to