SadServers - Linux & DevOps Troubleshooting Interviews

Troubleshooting Scenarios

Docker

Docker containers and repositories

#	Name	Level	Time	Type
1	"Salta": Docker container won't start.	Medium	15 m	Fix	"Salta": Docker container won't start. Scenario: "Salta": Docker container won't start. Level: Medium Type: Fix Access: Email Description: There's a "dockerized" Node.js web application in the `/home/admin/app` directory. Create a Docker container so you get a web app on port :8888 and can curl to it. For the solution to be valid, there should be only one running Docker container. Test: `curl localhost:8888` returns `Hello World!` from a running container. Time to Solve: 15 minutes.
2	"Venice": Am I in a container?	Medium	15 m	Do	"Venice": Am I in a container? Scenario: "Venice": Am I in a container? Level: Medium Type: Do Access: Email Description: Try and figure out if you are inside a container (like a Docker one for example) or inside a Virtual Machine (like in the other scenarios). Test: This scenario doesn't have a test (hence also no "Check My Solution" either). Time to Solve: 15 minutes.
3	"Tarifa": Between Two Seas	Medium	20 m	Fix	"Tarifa": Between Two Seas Scenario: "Tarifa": Between Two Seas Level: Medium Type: Fix Access: Email Description: There are three Docker containers defined in the docker-compose.yml file: an HAProxy accepting connetions on port :5000 of the host, and two nginx containers, not exposed to the host. The person who tried to set this up wanted to have HAProxy in front of the (backend or upstream) nginx containers load-balancing them but something is not working. Test: Running `curl localhost:5000` several times returns both `hello there from nginx_0` and `hello there from nginx_1` Check /home/admin/agent/check.sh for the test that "Check My Solution" runs. Time to Solve: 20 minutes.
4	"Helsingør": The first walls of postgres physical replication	Medium	20 m	Fix New	"Helsingør": The first walls of postgres physical replication Scenario: "Helsingør": The first walls of postgres physical replication Level: Medium Type: Fix Access: Email Description: You're setting up a PostgreSQL database with replication, you decided to use Docker along with Docker Compose to make it easier to manage and test, after a few hours of work you finished the job and the master database is up and running, but you're having trouble with the replica. You need to figure out what's wrong with the replica and fix it. Since you are using Docker Compose, you can check the status of the running containers using `docker compose ps` or `docker ps` will do the job too). You may also want to check the logs of the containers. All definition for the containers are inside the docker-compose.yml file. You can stand up the environment by running `docker compose up -d` and set it down by running `docker compose down`. If you make any change to the docker-compose.yml file, you can restart the containers by running `docker compose up -d --force-recreate`. Test: Postgres replica container works. The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute. Time to Solve: 20 minutes.
5	"Bern": Docker web container can't connect to db container.	Hard	20 m	Fix	"Bern": Docker web container can't connect to db container. Scenario: "Bern": Docker web container can't connect to db container. Level: Hard Type: Fix Access: Email Description: There are two Docker containers running, a web application (Wordpress or WP) and a database (MariaDB) as back-end, but if we look at the web page, we see that it cannot connect to the database. `curl -s localhost:80 \|tail -4` returns: `<body id="error-page"> <div class="wp-die-message"><h1>Error establishing a database connection</h1></div></body> </html>` This is not a Wordpress code issue (the image is :latest with some network utilities added). What you need to know is that WP uses "WORDPRESS_DB_" environment variables to create the MySQL connection string. See the ./html/wp-config.php WP config file for example (from /home/admin). Test: `sudo docker exec wordpress mysqladmin -h mysql -u root -ppassword ping` . The wordpress container is able to connect to the database in the mariadb container and returns `mysqld is alive`. Time to Solve: 20 minutes.
6	"Singara": Docker and Kubernetes web app not working.	Hard	20 m	Fix	"Singara": Docker and Kubernetes web app not working. Scenario: "Singara": Docker and Kubernetes web app not working. Level: Hard Type: Fix Access: Email Description: There's a k3s Kubernetes install you can access with kubectl. The Kubernetes YAML manifests under `/home/admin` have been applied. The objective is to access from the host the "webapp" web server deployed and find what message it serves (it's a name of a town or city btw). In order to pass the check, the webapp Docker container should not be run separately outside Kubernetes as a shortcut. Test: `curl localhost:8888` returns a value from the webapp deployed Kubernetes pod. Time to Solve: 20 minutes.
7	"Chennai": Pull a Rabbit from a Hat	Hard	30 m	Fix	"Chennai": Pull a Rabbit from a Hat Scenario: "Chennai": Pull a Rabbit from a Hat Level: Hard Type: Fix Access: Paid Description: There is a RabbitMQ (RMQ) cluster defined in a docker-compose.yml file. Bring this system up and then run the producer.py script in such a way that is able to send messages to RMQ. In particular you have to send the message "hello-lwc". - RMQ is a queuing system: messages are put in the queue with a "producer" and they are taken out from the other side by a "consumer". The queue name has to be the same for both. - To send the message "hello-lwc": `python3 ~/producer.py hello-lwc`. Should return `Message sent to RabbitMQ`. "IncompatibleProtocolError" means RMQ is not working properly. - To test consuming it: `python3 ~/consumer.py`, this will retrieve the next message from the queue and print it. Once everything is working send more than one message so there's at least one in the queue when the validation runs. - Do not change the consumer.py and producer.py files; if you do the Check My Solution will fail. Test: `python3 ~/consumer.py` returns `hello-lwc` See /home/admin/agent/check.sh for the exact test. Time to Solve: 30 minutes.
8	"Florence": Database Migration Hell	Hard	30 m	Fix New	"Florence": Database Migration Hell Scenario: "Florence": Database Migration Hell Level: Hard Type: Fix Access: Paid Description: You are working as a DevOps Engineer in a company and another team member left the company and left the docker-compose.yml of a database-backed web application unfinished. Generally, the problem revolves around the database migration and docker compose. Additionally on front of the application there is an Nginx server and you need to fix the proper access to it as well. The source of code is in /home/admin/app Credit Kamil Błaż Test: `curl --cacert /etc/nginx/certs/sadserver.crt https://sadserver.local` returns a message containing "ready to serve requests" The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute Time to Solve: 30 minutes.

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Updated: 2024-04-20 23:41 UTC – 9d41e63