🧭 Docker Port Mapping & CLI Flag CheatSheet
🚪 Port Mapping 101: -p vs -P
| Flag | Meaning | Analogy | Example |
-p <host>:<container> | Map host port to container port | Custom Door Mapping 🚪 | -p 8080:3000 |
-P (uppercase) | Auto-map all exposed ports to random host ports | 🔀 Auto Door Mapping | -P |
🎯 Example 1: Manual Mapping with -p
docker run -p 8080:3000 my-app
- 🔧 Host port 8080 mapped to container's 3000
- Access via
localhost:8080
🎲 Example 2: Auto Mapping with -P
docker run -P my-app
- Maps ALL
EXPOSEd ports to random available host ports - View with
docker ps
🌍 Multiple Port Mappings
docker run -p 3000:3000 -p 5000:5000 my-multi-app
- Maps multiple services/APIs or frontend/backend apps
- Great for full-stack containers!
📡 Exposing Ports in Dockerfile
EXPOSE 3000 5000 7000
| 🧠 Note: |
EXPOSE is just documentation for which ports the container listens to. |
It does not publish or map ports. Use -p or -P in docker run to do that. |
📦 Exposing a Range of Ports
docker run -p 8000-8010:8000-8010 my-app
- Useful for services like WebRTC, game servers, or load balancers needing multiple ports.
- 🔄 Keep range symmetrical between host and container.
🧪 Combine with --rm, -it, -d
| Flag | Meaning | Emoji | Use-case |
--rm | Auto-remove container when it exits | 🧹 | Clean test runs |
-i | Interactive (stdin open) | 🎤 | Needed for terminal apps |
-t | TTY (format output) | 🖥️ | Pretty output formatting |
-it | Combo: interactive + tty | 🧑💻 | Needed for shell, REPLs |
-d | Detached mode (run in background) | 🛸 | Long-running servers |
🔥 Full Command Example
docker run -it --rm -p 4000:3000 my-app
- Runs interactively
- Auto deletes after exit
- Maps port 3000 → 4000
🚀 Run in Detached Mode + Multiple Ports + Clean Exit
docker run -d --rm -p 3000:3000 -p 5000:5000 my-app
- Runs in background
- Auto-cleans after stopping
- Maps frontend + backend
🕵️♂️ How to Check Mapped Ports?
docker ps
| Column | What it Shows |
PORTS | Host:Container mapping (e.g., 0.0.0.0:8080->3000/tcp) |
🛑 Stop a Detached Container
docker stop <container_id>
🧠 Real-World Analogies
| Concept | Analogy |
| Container port | 📦 Internal phone extension |
| Host port | ☎️ Public phone number |
-p | Assigning specific number to extension |
-P | Letting system pick a number for you randomly |
✅ Summary Cheatsheet Table
| Option | Purpose | Usage |
-p 8080:80 | Manual port map | host:container |
-p 8000-8010:8000-8010 | Port range mapping | Bulk apps |
-P | Auto-map all exposed ports | Quick tests |
EXPOSE 3000 | Doc port in Dockerfile | Doesn't publish |
--rm | Auto-remove after exit | Clean containers |
-it | Interactive terminal | Needed for shell |
-d | Run in background | Daemonized apps |
🧾 Real Full Example: Production-style Run
docker run -d --rm \ -p 8080:80 \ -p 443:443 \ --name my-nginx \ nginx:alpine
✅ Starts Nginx with HTTP & HTTPS
✅ Cleans itself after docker stop
✅ Runs in background with custom name
🧠 Bonus Tip: Use --network to map ports between containers!
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