Docker Networking Mistakes and Solutions

Day 4 of my DevOps Journey 🚀 6 months ago I didn't know what Nginx was. Today I ran a full troubleshooting runbook on it. 🙌 If you're new to Linux and DevOps, here's the order I follow to verify a web server is healthy: 1️⃣ Check the OS & kernel — know your environment 2️⃣ Check CPU — top (99.9% idle = good) 3️⃣ Check Memory — free -h (3.2 GB free = good) 4️⃣ Check Disk — df -h (2% used = good) 5️⃣ Check Networking — ss -tuln (port 80 listening = good) 6️⃣ Verify service — curl http://localhost (200 OK = nginx is live) 7️⃣ Read logs — journalctl -u nginx (understand service history) No bootcamp. No course. Just hands-on practice on a real Ubuntu VM. If I can learn this, so can you. 💪 #Linux #Nginx #DevOps #Beginners #LearningInPublic #Ubuntu #SysAdmin #CareerChange #DevOpsEngineer #90DaysOfDevOps #DevOpsKaJosh #TrainWithShubham

The container was dying. No error. Just gone. docker logs showed nothing useful. I restarted it. It died again. I read the Dockerfile three times. Nothing. Then a colleague said: "check dmesg." `dmesg | grep -i kill` OOM killer. The kernel had killed it because the container hit its memory limit. Docker set the limit, but the kernel enforced it. And only the kernel's log had the real information. That moment changed how I used to debug containers. The Docker layer is thin. The answer is almost always one layer below. cgroups enforce resource limits. Namespaces create isolation. The kernel manages both. Docker is the interface, not the implementation. If you're only reading docker logs, you're reading the summary. The real story is in dmesg. #Docker #Linux #DevOps #Containers #Infrastructure #SoftwareEngineering #CloudNative #opensource

🚨 Application working but users still facing issues? Check logs like a pro Sometimes everything looks fine from your side… Service is running ✅ Server is up ✅ But users still report issues 😓 This is where logs become your best friend. --- 🔍 1. Start with application logs 👉 Check inside `/var/log` or app-specific folder 👉 Example: `tail -f /var/log/nginx/error.log` --- 📄 2. Look for keywords 👉 error 👉 failed 👉 timeout 👉 denied --- 🧠 3. Check timestamps 👉 Match logs with issue time 👉 Helps find exact event --- ⚡ 4. Check service logs `journalctl -u nginx` 👉 System-level logs for services --- 🌐 5. Correlate with user issue 👉 What user did? 👉 What happened in logs at same time? --- 🔁 6. Reproduce issue 👉 Try same steps 👉 Watch logs in real-time --- 🧠 Real mindset: Don’t guess ❌ Logs never lie ✅ --- #Linux #LinuxAdmin #DevOps #Troubleshooting #CloudComputing #SystemAdministration #LearningInPublic #ITInfrastructure

Kubernetes is not complicated. Your setup is. At its core, Kubernetes is just an abstraction on top of tools you already know. Linux namespaces, cgroups, iptables, DNS. It bundles them up, gives them a nice API, and calls it a day. That part is not the problem. The problem is everything you piled on top of it. The 47 admission controllers. The policy engines enforcing rules on plain YAML files. The custom operators for things that probably didn't need an operator. The internal platform that now sits between your engineers and the actual cluster. You didn't simplify ops, you just moved the complexity somewhere harder to see. And then troubleshooting becomes a nightmare. Not because Kubernetes is bad at surfacing problems, but because you've been working at the abstraction layer for so long that you forgot what's underneath. Something breaks and instead of checking what the kernel is actually doing, you stare at Helm values and wonder why the stars aren't aligned. The cluster isn't lying to you. Your understanding of it might be. What's the most convoluted thing you've seen someone do to a Kubernetes setup? I'm collecting horror stories 👻 .

Here's the mental model I wish I had when I started learning Docker. Not a diagram. A question. The question is: what changed? When you run a container, Linux creates a new set of answers to certain questions: What processes exist? What filesystems are mounted? What is the hostname? Before the container, those questions had the host's answers. After docker run, the process inside gets different answers. Same kernel. Different questions, different answers. The namespace is the mechanism that changes which answer the kernel returns. cgroups are completely separate. They don't change what the container sees. They change what the container is allowed to consume. Namespaces hide. cgroups limit. Most Docker mental models collapse these into one thing called "isolation." They're not the same, and knowing which one you need for which problem changes how you write Dockerfiles, configure orchestrators, and think about security. Not tutorials. Just a real picture. #Docker #Linux #DevOps #Containers #Infrastructure #CloudNative #SoftwareEngineering #MentalModel #OpenSource

gVisor gVisor provides a strong layer of isolation between running applications and the host operating system. It is an application kernel that implements a Linux-like interface. Unlike #Linux, it is written in a memory-safe language (Go) and runs in userspace. #gVisor includes an Open #Container Initiative (#OCI) runtime called runsc that makes it easy to work with existing container tooling. The runsc runtime integrates with #Docker and #Kubernetes, making it simple to run #sandboxed containers. https://lnkd.in/dvS8PBEa (by #Google)

New guide on getnix.io — "What is Nix?" A beginner-friendly intro to what Nix actually is, how it differs from Docker/Homebrew/Apt/Ansible, and the core concepts you need before diving in. If you've ever wondered why people keep talking about Nix, this one's for you. https://lnkd.in/ewR-S3Q8 #Nix #NixOS #Linux #macOS #DevOps #ReproducibleBuilds #PackageManagement

Most developers can build applications, but deploying them at the server level is where real understanding begins. As part of my training at Saylani Mass IT Training, our instructor Sir Nabeel Hassan not only introduced us to the fundamentals of web hosting using Nginx but also guided us through hands-on practice during the sessions. To take that learning further, I deployed one of my React/Vite projects locally on Ubuntu (WSL) using Nginx. This hands-on exercise involved: • Setting up a proper Linux development environment • Installing and configuring Node.js inside WSL • Debugging environment and version-related issues • Creating a production build of the application • Serving static files through Nginx • Writing and enabling a custom Nginx configuration • Testing and reloading the server What made this experience valuable was moving beyond managed platforms and understanding how deployment actually works under the hood, from build to server configuration. Grateful to Saylani SMIT and Sir Nabeel Hassan for emphasizing practical, hands-on learning. #DevOps #Nginx #Linux #WSL #React #WebServer #Deployment #SaylaniSMIT #CloudLearning

How to Install #Docker Engine on #Ubuntu #VPS Server This article provides a guide for how to install Docker Engine on Ubuntu VPS server. What is Docker? Docker is an application that utilizes OS-level virtualization to provide software in bundles called containers. While you can run Docker on any VPS, Ubuntu remains its most popular OS of choice. Containers provide an application's code, dependencies, libraries, and configuration files with their own secure environment, reducing the chance of any ... Keep Reading 👉 https://lnkd.in/gJVjZ67k #installguide #selfhosted #selfhosting #kvmvps #vpsguide #opensource

How to Install #Docker Engine on #Ubuntu #VPS Server This article provides a guide for how to install Docker Engine on Ubuntu VPS server. What is Docker? Docker is an application that utilizes OS-level virtualization to provide software in bundles called containers. While you can run Docker on any VPS, Ubuntu remains its most popular OS of choice. Containers provide an application's code, dependencies, libraries, and configuration files with their own secure environment, reducing the chance of any ... Keep Reading 👉 https://lnkd.in/gF6ApjAb #opensource #kvmvps #selfhosting #installguide #vpsguide #selfhosted