What is Docker and How It Changed Modern Web Development

What’s Docker?

Docker packages your app with everything it needs — code, libraries, settings — into a container. This container runs the same way everywhere. Your laptop, a server, the cloud. No more “works on my machine” problems.

Why Use Docker?

• Dev environments — New team member runs docker-compose up and everything’s ready in minutes
• Running websites — Web server, database, cache, job queues — each runs in its own container but they talk to each other
• Testing — Spin up different database versions, test, delete. Minutes not hours
• Legacy apps — Old PHP 5 app? Runs in its own container without messing with new stuff

Why It’s Great for Modern Websites

• Consistency — Same environment from dev to production
• Easy updates — Change Dockerfile, rebuild, done. Roll back in seconds if needed
• Simple scaling — More traffic? Run more containers
• Mix tech freely — Python API, Node frontend, Go workers — no dependency conflicts

How Is It So Lightweight?

Docker containers aren’t VMs. VMs run full operating systems (gigabytes of RAM, minutes to boot). Containers share the host OS kernel — megabytes in size, boot in seconds.

• Layered storage — 10 containers using Ubuntu? Stored once, shared by all
• Copy-on-write — Only copies files that actually change

Key Benefits

• Fast setup — One command instead of hours of installation
• Consistent environments — Defined in files, version controlled
• Isolation — One crash doesn’t affect others
• Cost savings — More apps on same hardware
• Huge ecosystem — Official images for Postgres, Redis, everything

Docker vs Alternatives

Feature	Docker	VMs	Podman	LXC	Bare Metal
Startup	Seconds	Minutes	Seconds	Seconds	N/A
Resources	Low	High	Low	Low	Lowest
Portability	Excellent	Medium	Good	Medium	Poor
Learning Curve	Easy	Medium	Easy	Hard	Varies
Community	Huge	Large	Growing	Small	N/A

• vs VMs — Docker shares host kernel, VMs need full OS. Run 20+ containers vs 3-4 VMs
• vs Podman — Podman is more secure but Docker has bigger ecosystem and better tooling
• vs LXC — LXC for systems, Docker for apps. Dockerfiles are simpler
• vs Bare Metal — No isolation vs clean isolation. Small overhead, huge sanity gains

Docker Swarm

Swarm runs containers across multiple servers as a cluster. Built into Docker.

How it works:

• Manager nodes — Decide which server runs what, handle failures
• Worker nodes — Run the containers
• Services — Define what to run, Swarm handles distribution

Why use it:

• High availability — server dies, containers move automatically
• Load balancing built-in
• Easy scaling — docker service scale web=10
• Rolling updates without downtime

Swarm vs Kubernetes

Feature	Docker Swarm	Kubernetes
Setup	Easy	Complex
Scaling	Good	Excellent
Best For	Small-medium	Enterprise
Learning Time	Hours	Weeks

Start with Swarm. Move to K8s when you outgrow it.

Downsides

• Learning curve exists
• Debugging inside containers can be tricky
• Mac/Windows runs Docker in a VM anyway
• Storage needs cleanup

Should You Use It?

Yes. It’s standard now. Start with one small app, play with docker-compose, break things. Not as hard as it looks.