Anyone who has deployed a simple web app on AWS knows this feeling: the infrastructure is up, CloudFormation says everything is green, the EC2 instances look fine… and yet the app refuses to load.
That’s exactly the kind of scenario this blog breaks down — a real, messy AWS failure involving EC2 instances behind an Application Load Balancer, and how Tetrix helps debug it with clarity and almost unfair speed.
Instead of spending hours jumping between the EC2 console, target groups, health checks, subnets, and security groups, Tetrix steps in like a DevOps co-pilot that sees the entire system and tells you exactly what’s broken.
Here’s how the whole thing unfolded.
The Problem: The App Was Alive, But AWS Wouldn’t Serve It
A web app was deployed behind an ALB through CloudFormation.
Everything looked fine on paper:
EC2 instances running
Security groups created
ALB provisioned
Outputs showing clean deployment
But when the ALB DNS was opened in a browser?
Nothing. No HTML. No logs. No hints.
Classic AWS mystery.
So the debugging began.
The Traditional Debugging Journey
1. Start with the Target Group
First stop: the Target Group under the load balancer.
And there it was — no registered instances.
If the ALB has no targets, it literally has nowhere to send traffic.
Fix: register the EC2 instances.
They appeared immediately… but with a twist:
both showed as “unhealthy.”
2. Check Why Targets Are Unhealthy
Unhealthy targets almost always mean one thing:
The health check is failing.
And yes — the health check path was set to /root, which the app didn’t expose at all.
Fix: change the health check path to /.
Health checks began passing, and the instances turned green.
Progress.
3. Still Not Working? Look at Security Groups
Even with healthy targets, the app still wasn’t loading.
So next up: inbound rules.
The EC2 security group was missing a simple but critical rule:
No inbound traffic on port 80 (HTTP).
So even though the ALB was forwarding traffic, the instances themselves were blocking it.
Fix: add inbound rule → HTTP / port 80 → allow traffic.
Another major blocker eliminated.
4. Everything Looks Fine… But the App Still Doesn’t Load
Now things got interesting.
Healthy targets?
Check.
Correct health check path?
Check.
Inbound rules?
Check.
And yet — still no response from the ALB.
This is where a lot of AWS debugging stalls. The obvious issues are fixed, but the app still isn’t reachable.
So one more area had to be checked.
5. The Real Culprit: Wrong Subnets
Digging into the ALB configuration revealed the final issue:
The ALB was deployed into private subnets.
An internet-facing load balancer sitting in private subnets is guaranteed to fail — it simply cannot accept external traffic.
Fix: switch the ALB to public subnets.
As soon as that change was applied, the app became reachable instantly.
Everything clicked into place.
Tetrix Caught It in Seconds — Literally
Normally, tracking down a subnet mistake like this eats up hours. You click through VPCs, compare subnet lists, double-check route tables, and keep wondering what you’re missing. But with Tetrix, it was almost unfairly easy. One prompt, a few seconds of processing, and it immediately pointed to the real problem: the ALB was sitting in private subnets, so of course nothing could reach it. Something that would’ve taken a whole afternoon to untangle was fixed in just minutes — because Tetrix actually understands your entire AWS setup at once.
Why This Matters
AWS issues almost never come from a single big mistake.
They come from:
one incorrect health check path
one missing inbound rule
one forgotten subnet choice
one target registration oversight
Each of these seems small.
Together, they take down your entire application.
What Tetrix does differently is simple but powerful:
Why Tetrix Makes This Entire Process Faster
Tetrix isn’t just another AI assistant — it has context.
When you connect your AWS account to Tetrix:
It ingests your VPC structure
Understands which EC2s belong to which ASGs
Sees the ALB, target groups, subnets, SG rules
Understands dependency graphs
Reads CloudFormation outputs
Maps relationships in real time
So when something breaks, Tetrix can reason like this:
“Targets are missing → You won’t get traffic.”
“Health check path is incorrect → Targets will be unhealthy.”
“Instance SG blocks port 80 → ALB cannot communicate.”
“ALB in private subnets → No internet access.”
It recreates the same mental map engineers build over years, but instantly.
This turns a multi-hour debugging session into a clear, guided sequence of steps.
What Tetrix Does Differently
Sees your entire system at once — code, infra, configs, and relationships all mapped into a single knowledge graph.
Reasons like a DevOps engineer — it understands how AWS services depend on each other.
Gives step-by-step debugging guidance — not vague suggestions, but actionable instructions.
Provides insights based on your live infrastructure — no generic AWS advice.
Turns “Why is this not working?” into a clear, solvable checklist.
Eliminates console-hopping — saving hours of manual digging across AWS dashboards.
A Simple Checklist for ALB Debugging
Here’s the distilled version of the entire journey — a checklist you can carry everywhere:
Target Group
✔️ Are your EC2 instances registered?
✔️ Do they show as healthy?
Health Check
✔️ Is the path correct (/ for most apps)?
Security Groups
✔️ Does the instance allow HTTP (port 80)?
✔️ Does the ALB have the right outbound rules?
Subnets
✔️ Is your ALB in public subnets if it is internet-facing?
Final Test
✔️ Does the ALB DNS respond to curl or browser open?
This combination solves the majority of “My ALB isn’t showing anything” issues.
The Bigger Picture
This debugging story highlights exactly why managing cloud infrastructure is tricky:
Too many dependencies
Too many hidden configuration traps
Too many ways a deployment can be “successful” but still broken
Tetrix steps in as your system-wide reasoning layer.
It doesn’t just answer questions — it understands how your cloud setup fits together.
That’s the real value of a DevOps co-pilot:
AI that can think across your entire system the way an experienced engineer does.
Resources
🌐 Learn more: https://www.deskree.com
📘 Docs: https://docs.deskree.com
🎥 Watch the full walkthrough: https://www.youtube.com/watch?v=0wK1uDf0ycg