Containers

General 13 questions

#1
Create Images on The Fly
Requirements

Have at least one image locally (run podman image ls to confirm).
If you don't have images locally, run simply podman pull nginx:alpine.

Objectives
1. Run a container using a web server image (e.g. httpd, nginx, ...)
- Bind container's port 80 to local port 80
- Run it in detached mode
- Name should nginx_container
1. Verify the web server runs and accessible
2. Create an HTML file with the following content and copy it to the container to the container to path where it will be accessed as an index file
```
<html>
<head>
<title>It's a me</title>
</head>
<body>
<h1>Mario</h1>
</body>
```
1. Create an image out of the running container and call it "nginx_mario"
2. Tag the container with "mario" tag
3. Remove the original container (container_nginx) and verify it was removed
4. Create a new container out of the image you've created (the same way as the original container)
5. Run curl 127.0.0.1:80. What do you see?
6. Run podman diff on the new image. Explain the output
Solution

Click here to view the solution
#2
Containerized DB
1. Run a container with a database of any type of you prefer (MySql, PostgreSQL, Mongo, etc.)
2. Verify the container is running
3. Access the container and create a new table (or collection, depends on which DB type you chose) for students
4. Insert a row (or document) of a student
5. Verify the row/document was added
#3
Containerized DB with Persistent Storage
1. Run a container with a database of any type of you prefer (MySql, PostgreSQL, Mongo, etc.)
2. Use a mount point on the host for the database instead of using the container storage for that
3. Explain why using the host storage instead of the container one might be a better choice
4. Verify the container is running
#4
Containerized Web Server
1. Run a containerized web server in the background and bind its port (8080) to a local port
2. Verify the port (8080) is bound
3. Reach the webserver from your local host
4. Now run the same web application but bound it to the local port 8080
#5
Layer by Layer
Objective

Learn about image layers

Requirements

Make sure Docker is installed on your system and the service is started
```
# Fedora/RHEL/CentOS
rpm -qa | grep docker
systemctl status docker
```
Instructions
1. Write a Dockefile. Any Dockefile! :) (just make sure it's a valid one)
2. Build an image using the Dockerfile you've wrote
3. Which of the instructions you've used, created new layers and which added image metadata?
4. What ways are there to confirm your answer to the last question?
5. Can you reduce the size of the image you've created?

Multi-Stage Builds

Objective

Learn about multi-stage builds

Instructions

Without actually building an image or running any container, use the following Dockerfile and convert it to use multi-stage:

FROM nginx
RUN apt-get update \
 && apt-get install -y curl python build-essential \
 && apt-get install -y nodejs \
 && apt-get clean -y
RUN mkdir -p /my_app
ADD ./config/nginx/docker.conf /etc/nginx/nginx.conf
ADD ./config/nginx/k8s.conf /etc/nginx/nginx.conf.k8s
ADD app/ /my_cool_app
WORKDIR /my_cool_app
RUN npm install -g ember-cli
RUN npm install -g bower
RUN apt-get update && apt-get install -y git \
 && npm install \
 && bower install \
RUN ember build — environment=prod
CMD [ “/root/nginx-app.sh”, “nginx”, “-g”, “daemon off;” ]

What are the benefits of using multi-stage builds?

#7
Run, Forest, Run!
Objective

Learn what restart policies do and how to use them

Requirements

Make sure Docker is installed on your system and the service is started
```
# Fedora/RHEL/CentOS
rpm -qa | grep docker
systemctl status docker
```
Instructions
1. Run a container with the following properties:
- image: alpine
- name: forest
- restart policy: always
- command to execute: sleep 15
1. Run docker container ls - Is the container running? What about after 15 seconds, is it still running? why?
2. How then can we stop the container from running?
3. Remove the container you've created
4. Run the same container again but this time with sleep 600 and verify it runs
5. Restart the Docker service. Is the container still running? why?
6. Update the policy to unless-stopped
7. Stop the container
8. Restart the Docker service. Is the container running? why?
#8
Running Containers
Objective

Learn how to run, stop and remove containers

Requirements

Make sure Podman or Docker (or any other containers engine) is installed on your system

Instructions
1. Run a container using the latest nginx image
2. List the containers to make sure the container is running
3. Run another container but this time use ubuntu latest and attach to the terminal of the container
4. List again the containers. How many containers are running?
5. Stop the containers
6. Remove the containers
#9
Sharing Images
Requirements

Have at least one image locally (run podman image ls to confirm).
If you don't have images locally, run simply podman pull httpd.

Objectives
1. Choose an image and create an archive out of it
2. Check the archive size. Is it different than the image size? If yes, what's the difference? If not, why?
3. Copy the generated archive to a remote host
4. Load the image
5. Verify it was loaded and exists on the remote host
Solution

Click here to view the solution
#10
Working with Images
Objective

Learn how to work with containers images

Requirements

Make sure Podman or Docker (or any other containers engine) is installed on your system

Instructions
1. List the containers images in your environment
2. Pull the latest ubuntu image
3. Run a container with the image you just pulled
4. Remove the image. Did it work?
5. Do whatever is needed in order to remove the image
#11
You’re a DevOps engineer deploying a Node.js application using Docker. You run docker run -d -p 3000:3000 my-node-app, but the container exits immediately. Using docker ps -a, you see the container status as Exited. How would you troubleshoot and resolve this issue?
#12
As a DevOps engineer, you need to deploy a web application with a Node.js backend and a MySQL database using Docker. The Node.js app connects to MySQL on localhost:3306, but running docker run for each container separately fails because they can’t communicate. How would you set up these containers to work together?
#13
You’re a DevOps engineer integrating a Dockerized Python application into a Jenkins CI/CD pipeline. The Dockerfile builds slowly, causing pipeline delays. How would you optimize the Dockerfile to speed up builds while maintaining functionality?

Containers 101 7 questions

#14
What is a Container?
#15
Why containers are needed? What is their goal?
#16
What is a container image?
#17
How are containers different from virtual machines (VMs)?
#18
In which scenarios would you use containers and in which you would prefer to use VMs?
#19
Describe the process of containerizing an application
#20
What are some of the advantages in using containers? you can compare to other options like VMs

Commands Commands 14 questions

#21
How to run a container?
#22
Why after running podman container run ubuntu the output of podman container ls is empty?
#23
How to list all the containers on the local host?
#24
How to attach your shell to a terminal of a running container?
#25
True or False? You can remove a running container if it doesn't running anything
#26
How to stop and remove a container?
#27
What happens when you run docker container run ubuntu?
#28
How to run a container in the background?
#29
If you'll run sleep 100 inside a container, will you see it when listing all the processes of the host on which the container runs? Why?
#30
True or False? If image httpd-service has an entry point for running the httpd service then, the following will run the container and eventually the httpd service podman run httpd-service ls
#31
True or False? Running podman restart CONTAINER_NAME kills the main process inside the container and runs it again from scratch
#32
You would like to run a web server inside a container but, be able to access it from the localhost. Demonstrate how to do that
#33
After running a container, it stopped. podman ps shows nothing. How can you show its details?
#34
How to list all the image tags for a given container image?

Images 64 questions

#35
Why container images are relatively small?
#36
You are interested in running a container with snake game application. How can you search for such image and check if it exists?
#37
How to list the container images on certain host?
#38
How to download/pull a container image without actually running a container?
#39
True or False? It's not possible to remove an image if a certain container is using it
#40
True or False? If a tag isn't specified when pulling an image, the 'latest' tag is being used
#41
True or False? Using the 'latest' tag when pulling an image means, you are pulling the most recently published image
#42
Where pulled images are stored?
#43
Explain container image layers
#44
True or False? Changing the content of any of the image layers will cause the hash content of the image to change
#45
How to list the layers of an image?
#46
True or False? In most cases, container images contain their own kernel
#47
True or False? A single container image can have multiple tags
#48
What is a dangling image?
#49
How to see changes done to a given image over time?
#50
What podman commit does?. When will you use it?
#51
True or False? Multiple images can share layers
#52
What is the digest of an image? What problem does it solves?
#53
True or False? A single image can support multiple architectures (Linux x64, Windows x64, ...)
#54
What is a distribution hash in regards to layers?
#55
How multi-architecture images work? Explain by describing what happens when an image is pulled
#56
How to check which architectures a certain container image supports?
#57
How to check what a certain container image will execute once we'll run a container based on that image?
#58
How to view the instructions that were used to build image?
#59
How docker image build works?
#60
What is the role of cache in image builds?
#61
How to remove an image from the host?
#62
What ways are there to reduce container images size?
#63
What are the pros and cons of squashing images?
#64
You would like to share an image with another developer, but without using a registry. How would you do it?
#65
True or False? Once a container is stopped and removed, its image removed as well from the host
#66
How to view the instructions that were used to build image?
#67
How to find out which files were added to the container image filesystem?
#68
True or False? podman diff works only on the container filesystem and not mounted files
#69
How the centralized location, where images are stored, is called?
#70
What is a Registry?
#71
A registry contains one or more ____ which in turn contain one or more ____
#72
How to find out which registry do you use by default from your environment?
#73
How to configure registries with the containers engine you are using?
#74
How to retrieve the latest ubuntu image?
#75
How to push an image to a registry?
#76
What are some best practices in regards to Container Images?
#77
What ways are there for creating new images?
#78
What are image tags? Why is it recommended to use tags when supporting multiple releases/versions of a project?
#79
How to tag an image?
#80
True or False? Once created, it's impossible to remove a tag for a certain image
#81
True or False? Multiple tags can reference the same image
#82
What is a Containerfile/Dockerfile?
#83
What instruction exists in every Containerfile/Dockefile and what does it do?
#84
List five different instructions that are available for use in a Containerfile/Dockerfile
#85
What are some of the best practices regarding Containerfiles/Dockerfiles that you are following?
#86
What is the "build context"?
#87
What is the difference between ADD and COPY in Containerfile/Dockerfile?
#88
What is the difference between CMD and RUN in Containerfile/Dockerfile?
#89
How to create a new image using a Containerfile/Dockerfile?
#90
Do you perform any checks or testing on your Containerfiles/Dockerfiles?
#91
Which instructions in Containerfile/Dockerfile create new layers?
#92
Which instructions in Containerfile/Dockerfile create image metadata and don't create new layers?
#93
Is it possible to identify which instruction create a new layer from the output of podman image history?
#94
True or False? Each Containerfile instruction runs in an independent container using an image built from every previous layer/entry
#95
What's the difference between these two forms:
```
ENTRYPOINT ["cmd", "param0", "param1"]
CMD ["param0"]

ENTRYPOINT cmd param0 param1
CMD param0
```
#96
Containerfile/Dockerfile can contain more than one ENTRYPOINT instruction and one CMD instruction
#97
What happens when CMD instruction is defined but not an ENTRYPOINT instruction in a Containerfile/Dockerfile?
#98
In the case of running podman run -it IMAGE ls the ls overrides the ___ instruction

Storage 5 questions

#99
Container storage is said to be ephemeral. What does it mean?
#100
True or False? Applications running on containers, should use the container storage to store persistent data
#101
You stopped a running container but, it still uses the storage in case you ever resume it. How to reclaim the storage of a container?
#102
How to create a new volume?
#103
How to mount a directory from the host to a container?

Architecture 6 questions

#104
How container achieve isolation from the rest of the system?
#105
What Linux kernel features does containers use?
#106
Describe in detail what happens when you run podman/docker run hello-world?
#107
Describe difference between cgroups and namespaces
#108
Which of the following are Linux features that containers use?
- cspaces
- namegroups
- namespaces
- cgroups
- ELlinux
- SElinux
#109
True or False? Containers have ephemeral storage layer

Docker Architecture 22 questions

#110
Which components/layers compose the Docker technology?
#111
What components are part of the Docker engine?
#112
What is the low-level runtime?
#113
What is the high-level runtime?
#114
True or False? The docker daemon (dockerd) performs lower-level tasks compared to containerd
#115
Describe in detail what happens when you run docker pull image:tag?
#116
Describe in detail what happens when you run a container
#117
True or False? Killing the Docker daemon will kill all the running containers
#118
True or False? containerd forks a new instance runc for every container it creates
#119
True or False? Running a dozen of containers will result in having a dozen of runc processes
#120
What is shim in regards to Docker?
#121
How would you transfer data from one container into another?
#122
What happens to data of the container when a container exists?
#123
How do you remove old, non running, containers?
#124
How the Docker client communicates with the daemon?
#125
Explain Docker interlock
#126
What is Docker Repository?
#127
Explain image layers
#128
What best practices are you familiar related to working with containers?
#129
How do you manage persistent storage in Docker?
#130
How can you connect from the inside of your container to the localhost of your host, where the container runs?
#131
How do you copy files from Docker container to the host and vice versa?

Docker Compose 5 questions

#132
Explain what is Docker compose and what is it used for
#133
Describe the process of using Docker Compose
#134
Explain Multi-stage builds
#135
True or False? In multi-stage builds, artifacts can be copied between stages
#136
What .dockerignore is used for?

Networking 1 question

#137
What container network standards or architectures are you familiar with?

Docker Networking 4 questions

#138
What network specification Docker is using and how its implementation is called?
#139
Explain the following blocks in regards to CNM:
- Networks
  - Endpoints
  - Sandboxes
#140
True or False? If you would like to connect a container to multiple networks, you need multiple endpoints
#141
What are some features of libnetwork?

Security 2 questions

#142
What security best practices are there regarding containers?
#143
A container can cause a kernel panic and bring down the whole host. What preventive actions can you apply to avoid this specific situation?

Docker in Production 9 questions

#144
What are some best practices you following in regards to using containers in production?
#145
True or False? It's recommended for production environments that Docker client and server will communicate over network using HTTP socket
#146
What forms of self-healing options available for Docker containers?
#147
What restart policies are you familiar with?
#148
Explain Rootless Containers
#149
Are there disadvantages in running rootless containers?
#150
Give one example of rootless containers are more safe from security perspective
#151
When running a container, usually a virtual ethernet device is created. To do so, root privileges are required. How is it then managed in rootless containers?
#152
When running a container, usually a layered file system is created, but it requires root privileges. How is it then managed in rootless containers?

OCI 2 questions

#153
What is the OCI?
#154
Which operations OCI based containers must support?

Scenarios 2 questions

#155
There is a running container that has a certain issue. You would like to share an image of that container with your team members, with certain environment variables set for debugging purposes. How would you do it?
#156
You and your team work on the same project, but different versions of it. For each version, the team creates a new, separate image. What would you suggest the team to change in such case?

Containers

Requirements

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