02 · The application, in containersLab 10 / 59
Challengedocker
Docker Networking, Volumes & Health Checks — Challenge
Make four containers find each other, keep data across a restart, and start in an order that actually works.
- Time
- 25 min
- Level
- Beginner
- Objectives
- 4 objectives
- Cost
- Free
Where this fits in the platform
This lab adds
- Containers that persist data and report their own health
Before you start
You will need
- Docker
- Docker Compose
You do not need these already — the lab environment below provides them.
You will be able to
- Reach one container from another by name
- Tell a bind mount from a volume, and pick correctly
- Use a health check to control startup order
The goal#
Achieve the same outcome as Docker Networking, Volumes & Health Checks, from an empty starting point, without the steps.
The application connects fine on your machine and fails in the pipeline with 'connection refused'. It starts before the database is ready, and everything it wrote last night is gone.
These three problems are the same three you will meet again as Services, PersistentVolumes and readiness probes — which is why this lab sits before Kubernetes.
Hands-on environment
Run this lab in a real terminal, free and in your browser. The environment is temporary and yours alone — break it as much as you like.
Start the challengeOpens in Killercoda, in a new tab — keep this page open for the steps.
This is the guided lab's environment — the same machine, with its walkthrough on the left. Work from the task above and leave those steps alone until you are done, or you are reading the answers.
Run it on your own machine
Run this lab on your own machine. One command starts the environment, with everything the lab needs already installed:
You will need:
- docker
git clone https://github.com/EgyKode/EgyKode-lab.git
cd EgyKode-lab
./egykode start
./egykode shellYou need Docker and Git installed. Everything else runs inside the environment. The first start downloads it and takes a few minutes; later starts are seconds.
Not sure what you already have? Run: npm run doctor — it checks and changes nothing.
Anything you tick here is your own record. EgyKode cannot see inside that terminal, so the success criteria stay self-assessed even when the environment checks your work for you.
What must be true when you are done
Step 1 of 3
What must be true when you are done#
- The application reaches PostgreSQL and Redis by service name, with no IP addresses anywhere.
- Database data survives
docker compose downand returns afterup. - The application waits for the database to be ready, not merely started.
- You can explain why two containers on different networks cannot see each other.
Rules#
- Do not open the guided lab until you are finished, or until the same problem has held you up for 20 minutes.
- Documentation is allowed and encouraged.
- Verify every criterion with a command whose output you can read.
If you get stuck#
- What did you expect, exactly?
- What happened instead — the error text, not a paraphrase?
- Which layer is that error from?
- What is the smallest command that proves the layer below is fine?
You are done when
0 of 4
The concept behind it
Next up
Lab 10 of 59 on the project path