# Guided Exercise: Diagnose Before You Recreate Anything

This is a paper exercise — commit to a diagnostic plan before working in the Lab.

## Your task

A container `payments-api` is reported as "unreachable" by a teammate. Before touching anything,
write out, in order, the exact commands you'd run to determine WHERE the problem actually is —
using this module's and ROOT 02's tools.

## A worked shape to check yourself against

```
docker ps --filter name=payments-api          # is it even running?
docker exec payments-api curl -sf localhost:PORT/    # does it work internally?
docker port payments-api                        # is anything actually published?
curl -sf http://localhost:PUBLISHED_PORT/       # does the published mapping actually work?
```

This sequence isolates each layer independently — running? working internally? published at
all? published mapping actually functional? — exactly the same "isolate one variable at a time"
discipline ROOT 02 Module 3 taught, applied here to containers specifically.

## Instructor Notes

**Facilitation:** This exercise is deliberately a direct copy of ROOT 02's diagnostic discipline
— the value is students recognizing that connection themselves, not being told it explicitly.

**Approximate timing:** 8-10 minutes live discussion; 5 minutes self-paced.