Docker Images

Question 1

What do docker images consist of?

Answer 1

Layers of files containing the differences between each layer

Question 2

What is the writable container layer?

Answer 2

Changes the container makes to its file system go into the top writable container layer, containing changes from the base layers

Question 3

How do you get an image?

Answer 3

docker image pull

Question 4

How do you view the layers within an image?

Answer 4

docker image history

Question 5

How do you build an image?

Answer 5

With a Dockerfile

docker build -t .

Question 6

Explain the following Dockerfile directives: FROM, ENV, RUN, CMD

Answer 6

FROM - starts build setting by base image
ENV - sets environment variables visible to file itself and container at runtime
RUN - creates layer on previous layer and commits changes
CMD - specify default command to run a container runtime

Question 7

Explain the following Dockerfile directives: EXPOSE, WORKDIR, COPY, ADD

Answer 7

EXPOSE - documents which ports intended to be published
WORKDIR - sets the current working directory for subsequent directives
COPY - copy files from local machine to image
ADD - copy, can also pull files from url

Question 8

Explain the following Dockerfile directives: STOPSIGNAL, HEALTHCHECK

Answer 8

STOPSIGNAL - specify the signal that will be used to stop the container
HEALTHCHECK - specify a custom health check to verify the container is working properly