Question / Problem scenario
You know what a Docker container is.  What is a Dockerfile and what is a Docker image?

Answer to What is a Dockerfile?
“Dockerfiles are used to define how a container should look at build time, but they do not manage the container’s ongoing state, and cannot be used to manage the Docker host system.” (Page 5 of Docker Up &

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Problem scenario
You are trying to run a Docker command, but you get this error:

Error parsing reference: ” continual/integration” is not a valid repository/tag.

What do you do?

Solution
Look to see if you have an extra “\” or space in your Docker run command.  That can cause this problem.

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Question
Dockerfile has reserved words CMD and ENTRYPOINT.  They seem to do the same thing.  What are the differences between CMD and ENTRYPOINT in Docker besides their words’ lengths?

Answer
There are many similarities between these two reserved words in Dockerfile “language.”  But here are three differences:

#1  “…CMD can be overwritten by an argument to docker run, while ENTRYPOINT can be overwritten only by using the –entrypoint option of docker run.” is a quote taken from page 43 of 

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Problem scenario
You want a Bash script to install Docker on any distribution of Linux.  You want to use the same script for each Linux server.  How do you write a script that will install docker-compose on any type of Linux including CentOS/RHEL/Fedora, Debian/Ubuntu and Linux SUSE?

Solution
Overview
This will work with AWS or Azure servers or on-premise servers.  It requires that the server have access to the internet.

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Problem scenario
You want to use the ENTRYPOINT and CMD keywords in a Dockerfile.  You know that the value of CMD amounts to a parameter for the ENTRYPOINT value which is executed.  You want to verify that the value of ENDPOINT is used in an execution.  You want the Dockerfile to be simple to illustrate these reserved words.  What do you do?

Solution
Prerequisite
Install Docker. 

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