DevOps Essentials

Question 1

A colleague says 'just run it in Docker' when you report that the app doesn't work on your machine. What does Docker provide?

Accepted Answer

Docker packages applications with their dependencies into containers - isolated environments that run consistently on any machine with Docker installed

Answer

Docker is a virtual machine that runs a complete operating system inside your computer

Answer

Docker is a cloud service that hosts your application on remote servers

Question 2

What does `docker-compose up` do with this configuration?

Accepted Answer

It starts both PostgreSQL and the app containers, waits for PostgreSQL to be ready, then starts the app, with ports mapped to localhost

Answer

It only starts PostgreSQL - the app must be started separately

Answer

It deploys the services to a cloud provider

Question 3

Your app running in Docker can't connect to PostgreSQL. The error says:

`Failed to connect to localhost:5432`

But PostgreSQL is running in another container. What's wrong?

Accepted Answer

`localhost` inside a container refers to that container itself, not other containers - use the service name (`postgres`) or Docker network IP instead

Answer

PostgreSQL isn't running - restart it

Answer

Docker doesn't allow containers to communicate - you need Kubernetes

Question 4

Your manager says to 'deploy to Kubernetes' instead of running Docker on a single server. What does Kubernetes add beyond Docker?

Accepted Answer

Kubernetes orchestrates containers across multiple machines - handling scaling, self-healing, load balancing, rolling updates, and service discovery automatically

Answer

Kubernetes is just Docker with a different name

Answer

Kubernetes replaces Docker - you can't use Docker with Kubernetes

Question 5

Your app is deployed to Kubernetes but something is wrong. Which commands help you debug?

Accepted Answer

`kubectl get pods` (check status), `kubectl describe pod ` (see events/errors), `kubectl logs ` (view application logs)

Answer

`kubectl deploy --debug` shows all issues automatically

Answer

You can only debug by accessing the cloud provider's web console

Question 6

The team mentions 'the CI/CD pipeline will deploy it'. What does CI/CD mean?

Accepted Answer

CI (Continuous Integration) automatically tests code on every commit; CD (Continuous Deployment) automatically deploys passing code to production

Answer

CI/CD is a testing framework like pytest

Answer

CI/CD is a Docker alternative for building containers

Question 7

You try to call your API at `http://localhost:8000` and get:

`Error: connect ECONNREFUSED 127.0.0.1:8000`

What does this error mean?

Accepted Answer

Nothing is listening on port 8000 - the application is not running or is running on a different port

Answer

The server is running but rejecting your request due to authentication

Answer

Your firewall is blocking the connection

Question 8

You run `docker-compose up -d` and the container appears briefly then disappears. `docker ps -a` shows:

`STATUS: Exited (1) 30 seconds ago`

How do you debug this?

Accepted Answer

Check the container logs with `docker logs <container>` to see why it crashed - exit code 1 means the app encountered an error

Answer

The image is corrupted - delete and re-pull it

Answer

Add `restart: always` to docker-compose.yml to keep it running

Question 9

You run your app and get:

`OSError: [Errno 48] Address already in use`

How do you fix this?

Accepted Answer

Find and stop the process using that port with `lsof -i :8000` then `kill <PID>`, or use a different port

Answer

Restart your computer - the port is permanently locked

Answer

Delete the .env file and try again

Question 10

The app needs a database password. You see:

`DB_PASSWORD = os.getenv("DB_PASSWORD")`

Where should the actual password value come from?

Accepted Answer

Set it as an environment variable - locally in `.env` file, in production via Kubernetes Secrets or cloud secret manager

Answer

Hardcode it in the Python file

Answer

Store it in a public GitHub repository so the team can access it