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tutorials/media-manager/docs/steps/install-docker.md

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+# Installing Docker — What It Is, How It Works, and Why We Use It
+
+Before installing Docker, it’s important to understand **what Docker actually does**, **how it fits into our media management setup**, and **why we run only the ARR stack inside Docker** while keeping **qBittorrent and Plex on the host system**.
+
+This page will walk you through all of that in simple, practical terms.
+
+---
+
+# 🐳 What Is Docker?
+
+Docker is a **containerization platform**.
+
+That means:
+
+### Docker lets you run applications in small, isolated environments called **containers**.
+
+A container:
+
+- has its own filesystem  
+- has its own dependencies  
+- has its own libraries  
+- cannot interfere with your main system  
+- can be destroyed and recreated easily  
+
+Think of it like:
+
+> **A lightweight, specialized mini-computer for one application.**
+
+This makes apps more predictable, easier to upgrade, and easier to manage.
+
+---
+
+# 🔧 Why Use Docker?
+
+### ✔ Avoid dependency conflicts  
+Containers ship the libraries the app needs, so you don’t pollute your main OS.
+
+### ✔ Easy to update  
+Updating Radarr/Sonarr/Prowlarr becomes:
+
+```
+docker compose pull
+docker compose up -d
+```
+
+### ✔ Easy to back up  
+ARR services store their config in a small folder you can snapshot.
+
+### ✔ Perfect for things that change often  
+Indexers break, Prowlarr updates, Radarr adds features — Docker makes it painless.
+
+---
+
+# 🚫 Why Not Put Everything in Docker?
+
+You *can* put everything in Docker, but in a real-world Raspberry Pi / home-server environment, some apps **behave badly** or **have limitations** inside containers.
+
+Below is the reasoning for each major component.
+
+---
+
+# ❌ Why qBittorrent Is NOT in Docker
+
+### qBittorrent needs:
+- fine-grained permission control
+- direct disk access  
+- stable file paths  
+- high-speed I/O for torrent hashing  
+- ability to handle sudden restarts and disk states  
+
+Inside Docker, qBit often has problems:
+
+| Problem | Why It Happens |
+|--------|----------------|
+| Slow hashing | Docker’s overlay filesystem adds overhead |
+| Permission issues | Containers struggle with mixed UID/GID + bind mounts |
+| Inconsistent paths | qBit expects real Linux paths for completed downloads |
+| Harder integration | Radarr/Sonarr sometimes misread container-mapped paths |
+
+### 🧠 Therefore:
+**qBittorrent on the host is cleaner, faster, and more stable.**
+
+---
+
+# ❌ Why Plex Is NOT in Docker
+
+This is even more important.
+
+### Plex inside Docker struggles with:
+
+| Feature | Issue in Docker |
+|--------|-----------------|
+| **Hardware transcoding (VAAPI/V4L2/QuickSync)** | Often broken or requires special setup |
+| **Direct I/O from large libraries** | Docker overlay adds slowdowns |
+| **Automatic network discovery** | Plex uses multicast/IGMP which Docker isolates |
+| **Large metadata directories** | Docker containers don’t like millions of tiny files |
+
+Plex has a massive, constantly evolving I/O profile and **performs best on bare metal** (host).
+
+### 🧠 Therefore:
+**Install Plex directly on the host for speed, compatibility, and transcoding support.**
+
+---
+
+# 🟩 Why the ARR Stack *Is* in Docker
+
+Radarr, Sonarr, and Prowlarr:
+
+- are lightweight  
+- use clean, simple paths  
+- store configuration in manageable folders  
+- benefit from frequent updates  
+- rarely need hardware access  
+- behave very predictably in containers  
+
+They’re practically **designed to live inside Docker**.
+
+### ✔ Consistent paths  
+As long as `/mnt/omnissiah-vault` is mounted, containers have zero issues.
+
+### ✔ Easy migrations  
+Moving to a new server is as simple as:
+
+```
+copy configs → run docker-compose → done
+```
+
+### ✔ Better isolation  
+If Radarr breaks from an update, it won’t affect Plex or qBit.
+
+---
+
+# 🧱 Summary — The Architecture Philosophy
+
+| Component | Host or Docker? | Reason |
+|----------|------------------|---------|
+| **Docker Engine** | Host | Foundation layer |
+| **ARR Stack (Radarr / Sonarr / Prowlarr / Bazarr)** | Docker | Best candidates for containers |
+| **qBittorrent** | Host | Needs stable I/O + real filesystem access |
+| **Plex** | Host | Needs hardware transcoding + network discovery |
+
+This hybrid approach gives us the **best combination of performance, stability, and maintainability**.
+
+---
+
+# 🧰 Installing Docker (Raspberry Pi / Linux)
+
+Here is the installation script referenced in the flow:
+
+### 📥 Download Script  
+👉 **[install-docker.sh](../scripts/shell/install-docker.sh)**  
+
+### 🖥️ What the script does  
+- updates the system  
+- removes conflicting old packages  
+- installs Docker using the official convenience script  
+- installs Docker Compose  
+- adds your user to the docker group  
+- enables and starts the Docker service  
+- verifies installation  
+
+After running it:
+
+```bash
+sudo reboot
+```
+Your system will be ready to run containerized ARR services.
+
+# 🚀 Next Step: Configure Plex (Host Installation)
+Once Docker is installed, we move forward with:
+👉 Install Plex (steps/install-plex.md)
+This ensures the server is ready to serve media once the ARR stack begins populating it.