Diego Herrera

DevOps | SRE | Cloud engineer

[Nandkishor @devops_nk]

AWS DevOps Interview Question 🚨

Your EC2 instance has:
✅ Public IP assigned
✅ Port 22 allowed in Security Group
✅ EC2 Instance Connect working from AWS Console

But SSH using the PEM key from your laptop fails.

What could be the possible reasons and how would you troubleshoot it?

[Linux Inside: The Ideal Blog for Sysadmins & Geeks @tecmint]

Most sysadmins have a folder of Bash scripts they didn't write and are afraid to touch.

In Chapter 12 of our #ClaudeCode for #Linux #Sysadmins course, you'll write a real backup script from scratch, have Claude review it for edge case bugs, and refactor an inherited log cleanup script with 10 real issues hiding in 12 lines.

Read it here → https://t.co/UFrOdkHq2Y

Follow @tecmint for a new chapter every week.

[Miguel Ángel Durán @midudev]

Acabo de encontrar una web que explica los códigos HTTP… usando memes. 200, 404, 500 y compañía.

Aprender HTTP así debería ser obligatorio en primero de programación.

→ https://t.co/vJj1o3DHaj

[AsyncTrix @asynctrix]

Docker Junior vs Senior 🔥

• Junior: docker build -t app .
• Senior: Multi-stage + cache optimization + Trivy scan

• Junior: Runs as root
• Senior: USER nonroot + least privilege

It works on my machine is now It works in my container

Full breakdown 👇

[Dhanian 🗯️ @e_opore]

LINUX ROADMAP 2026: COMPLETE LEARNING PATH
│
├── 1. Introduction to Linux
│ ├── What is Linux
│ ├── Linux distributions (Ubuntu, Fedora, Debian)
│ └── Linux architecture and kernel basics
│
├── 2. Linux Installation & Setup
│ ├── Installing Linux on a PC or VM
│ ├── Dual boot and virtualization
│ └── Understanding the Linux file system
│
├── 3. Linux Command Line Basics
│ ├── Navigating directories (cd, ls, pwd)
│ ├── Creating and managing files
│ └── Understanding terminal workflows
│
├── 4. Working with Files & Permissions
│ ├── chmod, chown, and permissions
│ ├── File compression and archiving
│ └── Searching files with find and grep
│
├── 5. Users & Process Management
│ ├── Managing users and groups
│ ├── Monitoring processes (ps, top, htop)
│ └── Process control and scheduling
│
├── 6. Shell Scripting
│ ├── Bash scripting fundamentals
│ ├── Variables, loops, and functions
│ └── Automating repetitive tasks
│
├── 7. Package Management
│ ├── APT, DNF, and YUM
│ ├── Installing and updating software
│ └── Managing repositories
│
├── 8. Networking in Linux
│ ├── IP addressing and DNS
│ ├── SSH and remote access
│ └── Network troubleshooting tools
│
├── 9. Linux System Administration
│ ├── System services and systemd
│ ├── Log management and monitoring
│ └── Disk management and backups
│
├── 10. Linux Security
│ ├── Firewall configuration
│ ├── User authentication and SSH security
│ └── Security best practices
│
├── 11. Linux for DevOps & Cloud
│ ├── Docker fundamentals
│ ├── Kubernetes basics
│ └── Cloud server management
│
├── 12. Linux Server Administration
│ ├── Web server setup (Nginx, Apache)
│ ├── Database server management
│ └── Performance tuning and optimization
│
└── 13. Practice & Career Growth
├── Real-world Linux projects
├── Linux certifications (LFCS, RHCSA)
└── Continuous learning and troubleshooting

Recommended Ebook
→ Grab the Complete Linux Handbook
→ https://t.co/DeHjJ1Wubf

[Miguel Ángel Durán @midudev]

Si eres Programador Web y usas IA... ¡Instala esto!
Agent Skills de Addy Osmani (de Google) para:

✓ Rendimiento Web
✓ Mejores prácticas
✓ Accesibilidad
✓ SEO

Para React, Vue, Angular, Astro o lo que uses.
$ npx add-skill addyosmani/web-quality-skills

[Valen @ValenSecurity]

Event Driven Architecture: en vez de guardar el estado actual, guardás el historial completo de eventos y construís el estado como una proyección del pasado. El futuro del desarrollo 🔥 #EventDrivenArchitecture #SoftwareEngineering #Programacion

[Nandkishor @devops_nk]

Docker Networking Types Explained 🧵

Understanding Docker networking is important for DevOps interviews because it determines how containers communicate with each other and the outside world.

1️⃣ Bridge Network (Default)

What it is:
When you start a container without specifying a network, Docker attaches it to the bridge network.
How it works:
• Docker creates a virtual bridge called docker0
• Each container gets a private IP
• Containers on the same bridge can communicate with each other
• External traffic reaches containers through port mapping

Example:
docker run -d -p 80:80 nginx
Use when:
• Running standalone applications
• Local development
• Single-host deployments

----------------------------------------------

2️⃣ Host Network
What it is:
The container shares the host machine's network stack.

How it works:
• No separate container IP
• No NAT
• No port mapping required
• Container uses host ports directly

Example:
docker run --network host nginx
Use when:
• Maximum network performance is required
• Monitoring agents
• Logging agents

Interview Tip:
Host networking is faster because packets don't go through Docker's virtual networking layer.

--------------------------------------

3️⃣ None Network
What it is:
Container gets no network connectivity.
How it works:
• No IP address assigned
• No internet access
• No communication with other containers

Example:

docker run --network none nginx

Use when:
• High-security workloads
• Batch processing jobs
• Isolated testing

-----------------------------------------

4️⃣ Overlay Network
What it is:
Allows containers running on different Docker hosts to communicate.

How it works:
• Creates a virtual network across multiple hosts
• Uses VXLAN tunneling
• Commonly used with Docker Swarm

Example:
docker network create -d overlay my-network

Use when:
• Multi-host container communication
• Docker Swarm clusters
• Distributed applications

-------------------------------------------

5️⃣ Macvlan Network
What it is:
Assigns a real IP address from the physical network to the container.

How it works:
• Container appears as a separate device on the network
• Bypasses Docker bridge networking
• Direct communication with physical devices
Use when:
• Legacy applications
• Network appliances
• Applications requiring direct Layer 2 access

Summary:
✅ Bridge → Default, most common
✅ Host → Best performance
✅ None → Complete isolation
✅ Overlay → Multi-host communication
✅ Macvlan → Real IP for containers

[Linux Inside: The Ideal Blog for Sysadmins & Geeks @tecmint]

💡 Quick Linux Tip #17
Need to see live system performance without installing anything?

Use:

$ top

This shows real-time CPU usage, memory usage, and running processes.

Useful shortcuts while top is running:

Press P to sort processes by CPU usage

Press M to sort processes by memory usage

Press q to quit

If you want a cleaner and more interactive view, try:

$ htop

This provides a more user-friendly way to monitor CPU, memory, load averages, and running processes in real time.

Follow @tecmint for more #Linux tips

[Linux Inside: The Ideal Blog for Sysadmins & Geeks @tecmint]

Most Linux users know containers are "lighter than virtual machines", but aren't quite sure why.

In Chapter 21 of our #LFCA Certification Course, you'll learn what makes containers different, including Linux namespaces, cgroups, kernel sharing, container images, and how #Docker runs applications in isolated environments.

Read it here → https://t.co/eHU1cJRgmG

Follow @tecmint for a new chapter every week.

#Docker #LinuxAdmin #DevOps #SysAdmin

[Dhanian 🗯️ @e_opore]

Docker logging and monitoring architecture

[Balogun Hammed @bhalloinfraguy]

Infrastructure Concept — explained:

What are Sticky Sessions?

You have a load balancer in front of 3 application servers. A user logs in. The load balancer sends them to Server 1. Server 1 stores its session in memory.

The user clicks the next page. The load balancer might send them to Server 2. But Server 2 doesn't know they're logged in. They get logged out.

That's the problem sticky sessions solve.

Sticky sessions (also called session affinity) tell the load balancer: "If a user landed on Server 1 once, keep sending them to Server 1."

How it works:
→ The load balancer adds a cookie that identifies which backend handled the user
→ Or it uses the source IP to consistently route to the same server
→ Future requests from the same user hit the same server every time

When to use sticky sessions:
→ Applications that store session data in local server memory
→ Legacy apps that can't share session state
→ When you can't easily move sessions to Redis or a database

When NOT to use them:
→ When servers can fail, the user loses their session if their server dies
→ When you want even traffic distribution, sticky sessions cause uneven load
→ When you have proper external session storage (Redis, Memcached)

Better solution: store sessions in a shared cache like Redis. Any server can read them. The load balancer can route however it wants. The user stays logged in no matter where they land.

Sticky sessions are a workaround. Stateless apps with shared session storage are the right way.

[Valen @ValenSecurity]

No necesitás saberlo todo. Operá con lo que sabés, resolvé problemas y tu universo de soluciones se irá agrandando solo. Así crece una carrera 💡 #desarrolloprofesional #programacion #aprendizaje

[Ayaan 🐧 @twtayaan]

The 9 Layers of DevOps

1⃣ Culture & Collaboration: Build shared ownership, communication, and continuous improvement.

2⃣ Plan: Define requirements, priorities, and the roadmap.

3⃣ Code: Write, review, and secure application code.

4⃣ Build: Compile code, create artifacts, and package applications.

5⃣ Test: Validate functionality, performance, and security.

6⃣ Release: Prepare and approve changes for production.

7⃣ Deploy: Deliver applications reliably using automation and IaC.

8⃣ Operate: Monitor systems, manage incidents, and maintain reliability.

9⃣ Optimize: Improve performance, reduce costs, and learn from feedback.

[Nandkishor @devops_nk]

One Kubernetes interview question I keep getting asked:

"Walk me through what happens when a request travels from the Internet to a Pod."

Most candidates answer:

User → ALB → Ingress → Service → Pod

But that's just the beginning.

The follow-up questions are where things get interesting:

• Who actually decides which Pod gets the request?
• What does kube-proxy do?
• How do iptables/IPVS work?
• What role does the CNI plugin play?
• If kube-proxy crashes, does traffic stop?

My biggest learning:
- A Kubernetes Service is not a load balancer by itself.
- kube-proxy programs iptables/IPVS rules on the nodes, and those rules are what actually route traffic to healthy Pods.

Even more interesting:
- If kube-proxy crashes, existing traffic usually keeps working because the networking rules already exist in the kernel.
- What breaks is the ability to update those rules when Pods or Services change.

Sometimes the simplest interview questions expose the deepest gaps in our Kubernetes knowledge.

[Linux Inside: The Ideal Blog for Sysadmins & Geeks @tecmint]

In this article, I’ll walk you through the 20 most essential Linux commands every system administrator should know.

These everyday tools help you monitor performance, manage services, check disk usage, read logs, and troubleshoot problems on modern Linux systems.

👉 https://t.co/RELYYk1KXc

Follow @tecmint for more #Linux tips...

[Miguel Ángel Durán @midudev]

¡BRUTAL! Un entorno virtual de Linux en tu navegador.

✓ Sin instalaciones. Usa Web Assembly
✓ Trae Python, C, C++, Vim, cURL y más
✓ Con conexión a Internet para instalar lo que quieras

¡Pruébalo y alucina! → https://t.co/1nqUVWwRNf

[Linux Inside: The Ideal Blog for Sysadmins & Geeks @tecmint]

Quick Linux Tip #13

Need to compare two config files and need to see what changed between two config files?

Use:

diff -u config_old.txt config_new.txt

This compares both files and highlights the differences. Lines starting with - were removed or changed, and lines starting with + were added or updated.

The -u option also shows a few lines around each change, making it easier to understand what was modified.

Instead of checking files line by line, you can quickly spot what was edited and troubleshoot faster.

Follow @tecmint for more #Linux tips

[Linux Inside: The Ideal Blog for Sysadmins & Geeks @tecmint]

Quick Linux Tip #11

Need to find exactly when you ran a command without scrolling endlessly through shell history?

First, enable timestamps:

$ export HISTTIMEFORMAT="%F %T "

Then search your history:

$ history | grep ssh

This lets you quickly find commands and see the exact date and time they were executed.

For even faster searching, press Ctrl+R and start typing. Bash will search your history interactively as you type.

Once you know these shortcuts, you'll never spam the up arrow again.

Follow @tecmint for more #Linux tips

[Miguel Ángel Durán @midudev]

Alternativa gratuita y de código abierto a NotebookLM
Genera podcasts y chatea con tus documentos fácil.

Sin suscripciones, desde tu máquina y usas la IA que quieras. 100% privado:
https://t.co/otT4EB81tG