📝 Essential Flags to Remember


# Run in detached mode (in background)
-d
 
# Interactive mode (with TTY)
-it
 
# Remove container after exit (auto-cleanup)
--rm
 
# Set container name
--name my_container
 
# Port mapping
-p host_port:container_port
 
# Volume mounting
-v host_path:container_path
 
# Environment variables
-e VAR=value
 
# Read-only root filesystem
--read-only
 
# Resource limits
--memory="512m" --cpus="1.0"

🖥️ Virtual Machine vs Container — Comparison Table

Feature	Virtual Machine (VM)	Container
Definition	A VM emulates an entire physical computer system including the OS and hardware.	A container virtualizes only the OS user space, sharing the host kernel.
Isolation Level	Full hardware-level isolation (each VM runs its own OS).	Process-level isolation (containers share the host OS kernel).
Boot Time	Slow — minutes (full OS startup).	Fast — seconds (lightweight and shares OS).
Resource Usage	Heavy — needs its own OS, uses more RAM & CPU.	Lightweight — shares kernel, minimal overhead.
OS Dependency	Each VM can run a different OS.	Must use the same OS kernel as the host.
Storage Size	Large — typically in GBs (full OS image).	Small — typically in MBs (application image).
Performance	Slightly slower due to hypervisor overhead.	Near-native performance since kernel is shared.
Security	Strong isolation; one VM cannot easily affect another.	Weaker isolation (kernel shared); uses namespaces & cgroups.
Scalability	Slower to scale; more resource-intensive.	Highly scalable; quick to spin up/down containers.
Portability	VM images are less portable; depend on hypervisor.	Highly portable across environments supporting container runtimes (Docker, Podman, etc.).
Management Tooling	Managed using hypervisors (VMware, VirtualBox, Hyper-V).	Managed using container runtimes & orchestrators (Docker, Kubernetes).
Use Case	Best for running multiple OS environments or legacy apps.	Best for microservices, CI/CD pipelines, and lightweight deployments.
Example Technologies	VMware, VirtualBox, KVM, Hyper-V	Docker, Podman, Kubernetes, LXC

🔍 Summary

VMs: Heavy, secure, ideal for full OS isolation.
Containers: Lightweight, fast, ideal for modern cloud-native and microservice architectures.

📘 Note: Containers are often used within VMs in enterprise setups for additional isolation and control.

🖥️ Virtual Machine vs Container — Simple Comparison (with Kernel Space)

Topic	Virtual Machine (VM)	Container
What it is	A VM is like a full computer inside your computer. It runs its own operating system and kernel.	A container is a small, fast box that runs an app using your computer’s operating system and shares its kernel.
Kernel Space	Each VM has its own kernel space, separate from the host.	All containers share the same kernel space of the host system.
How it works	Needs its own copy of the operating system and virtual hardware (through a hypervisor).	Shares the same OS kernel but keeps separate user spaces for each app.
Speed	Slower to start because it loads a whole OS and kernel.	Starts very fast because it uses the host kernel and skips booting a full OS.
Resource Use	Uses a lot of memory and CPU — runs its own OS and kernel.	Uses much less memory and CPU — shares the kernel with others.
OS Requirement	Can run different OS types (Windows, Linux, etc.).	Must use the same kernel type as the host (e.g., all Linux-based).
Size	Large (often several GB).	Small (often a few MB).
Performance	Slightly slower because of the extra OS layer.	Very fast — almost like running directly on the machine.
Security	More secure — each VM is fully separated, including its kernel.	Less isolated — if the shared kernel is attacked, all containers may be affected.
Scalability	Harder to create and run many VMs quickly.	Very easy to create and destroy containers in seconds.
Portability	Harder to move between systems (depends on hypervisor).	Easy to move anywhere that supports Docker or Kubernetes.
Tools	Managed using VirtualBox, VMware, Hyper-V, etc.	Managed using Docker, Podman, Kubernetes, etc.
Best For	Running full OS setups, different OS types, or legacy systems.	Running small, lightweight apps and microservices.

🧩 In Short

VMs: Have their own kernel, are big and safe, good for full systems.
Containers: Share the same kernel, are small and fast, good for apps.

📘 Tip: In many systems, containers run inside VMs — combining speed and extra safety.