Because if your service isn’t listening on the right port, is it even alive?

One of the first things I had to figure out as I got deeper into DevOps was this:

What protocols run where, and why does every tool ask about ports?!

So I made a cheat sheet — not just to remember the ports, but to understand why these protocols matter in DevOps day-to-day work.

This blog is that cheat sheet, cleaned up and shared. If you're doing the #90DaysOfDevOps2025 like me — here's your Protocols & Ports breakdown 👇

📖 What Are Protocols & Ports?

Before diving in, let’s get the basics out of the way:

A protocol is a set of rules for communication between devices. Think of it like a language (e.g., HTTP for web, SSH for remote login).
A port is like a channel inside a machine. Each protocol usually uses a default port — so tools and services know where to listen or talk.

For example, if you're serving a website over HTTPS, the server listens on port 443, and clients automatically expect it there.

📋 Most Common Protocols & Ports in DevOps

Here’s the core list I use again and again in projects, cloud deployments, CI/CD tasks, and container setups:

Protocol	Port	Use Case	DevOps Relevance
HTTP	80	Unsecured web traffic	Serving sites, APIs, probes
HTTPS	443	Secured web traffic (TLS/SSL)	Hosting secure apps, frontend-backend comm
SSH	22	Remote terminal login	Server access, Git over SSH
FTP	21	File transfer	Legacy systems, rare in modern pipelines
SFTP	22	Secure FTP (over SSH)	Transferring logs securely
DNS	53	Resolves domain names	Custom domains, service discovery
SMTP	25	Sending emails	Alerting, notification systems
POP3	110	Receiving emails	Rare, legacy support
IMAP	143	Receiving emails (advanced)	Email alerts integration
MySQL	3306	MySQL DB access	Database connections in apps
PostgreSQL	5432	PostgreSQL DB access	Common in SaaS & cloud-native tools
MongoDB	27017	NoSQL DB access	Storing logs, events, analytics data
Redis	6379	In-memory data store	Caching, pub/sub, job queues
Elasticsearch	9200	Search engine queries	Log storage (e.g., ELK stack)
Kubernetes API	6443	Cluster management	Used by `kubectl`, CI tools, etc.

Let’s break down where you’ll actually touch these protocols:

Used constantly for accessing remote servers or containers.

Runs everything on the web — your backend, frontend, dashboards, APIs.

Your apps need data — securely and consistently.

Used for performance tuning and log storage.

Used when your app or server needs to send or receive alerts.

A misconfigured DNS record can break everything.

When something isn’t working, I always do this first:

bashCopyEdit# Check if port is open
nc -zv <hostname> 22

# Or test HTTP/HTTPS endpoint
curl -I http://your-api.com

# For DNS
dig yourdomain.com

Sometimes it’s just a closed port in your firewall or security group.