Docker Flashcards
What is required for Docker to run on Windows?
At least Win10
or
Hyper-V enabled
Dockerfile
FROM ubuntu
Run mkdir tmplogs
RUN apt-get install vim
RUN apt-get install htop
Dockerfile - layers?
Each line of the Dockerfile is a layer!
Docker image?
A read-only template that forms the foundation of your application
Docker Container
a Docker image, when it’s run in a host computer, spawns ta process with its own namespace
When container is stopped/killed…?
All changes are lost
Ways to mount data?
Volumes, Bind Mounts, tmpfs
Docker Registry?
Place to store your Docker images
Dockerfile Layers - defined
A FROM instruction that tells Docker what the base image is
An ENV instruction to pass an environment variable
A RUN instruction to run some shell commands (for example, install-
dependent programs not available in the base image)
A CMD or an ENTRYPOINT instruction that tells Docker which executable to
run when a container is started
Docker Engine
Docker Engine is the core part of Docker. Docker Engine is a client-server
application that provides the platform, the runtime, and the tooling for building
and managing Docker images, Docker containers, and more.
Docker CLI commands (the basics)
docker build
docker pull
docker run
docker exec
Docker Compose
Docker Compose is a tool for defining and running multi-container applications
Docker Registry (may need authentication)
the registry is hosted on dockerprivate.registry
WORKDIR
WORKDIR instruction sets the current working directory for RUN, CMD,
ENTRYPOINT, COPY, and ADD instructions
FROM
FROM
As you learned earlier, every image needs to start from a base image
ADD & COPY
ADD and COPY instructions seem to do the same—they allow
you to transfer files from the host to the container’s filesystem
ADD & COPY - differences
COPY supports
basic copying of files to the container, while ADD has support for features like
tarball auto extraction and remote URL support
RUN Command
RUN (known as the shell form) RUN ["executable" , "parameter 1" , " parameter 2"] (known as the exec form)
RUN Example
RUN apt-get update RUN apt-get install foo RUN apt-get install bar RUN apt-get install baz It’s better to wrap them in a single RUN command: RUN apt-get update && apt-get install -y \ foo \ bar \ baz
CMD & ENTRYPOINT
CMD and ENTRYPOINT instructions define which command is executed when
running a container
ENV
The ENV instruction sets the environment variables to the image
VOLUME
The VOLUME instruction tells Docker to create a directory on the host and mount
it to a path specified in the instruction.
EXPOSE
The EXPOSE instruction tells Docker that the container listens for the specified
network ports at runtime
LABEL
The LABEL instruction adds metadata to an image as a key/value pair.
Data Persistence
Traditionally, VMs store persistent data, containers do, usually, not
Strategies to persist data
mpfs mounts
Bind mounts
Volumes
tmpfs Mounts
The directories mounted in tmpfs appear as a
mounted filesystem but are stored in memory, not to persistent storage such as a
disk drive.
Bind Mounts
In bind mounts, the file/directory on the host machine is mounted into the
container.
Bind Mount VS. Docker Volume
By contrast, when using a Docker volume, a new directory is created
within Docker’s storage directory on the Docker host and the contents of the
directory are managed by Docker
Preferred flag for Mounting?
–mount
Example of Mount
mounting host’s home directory, to a directory called ‘host-name’ within the container
docker run -it --name mount-test --mount type=bind,source="$HOME" ,target=/host-home ubuntu bash docker run -it --name mount-test -v $HOME:/host-home ubuntu bash
Volumes
Docker volumes are the current recommended method of persisting data stored
in containers
Volume Advantages
Volumes are easier to back up or transfer than bind mounts
Volumes work on both Linux and Windows containers
Volumes can be shared among multiple containers without problems
Docker Volume Commands
docker volume create docker volume inspect docker volume ls docker volume prune docker volume rm
Example Volume command
docker volume create –name=nginx-volume
Default Docker Network Drivers
bridge host overlay macvlan none
Bride Network
Allows for containers to communicate together
Host Network
Connects containers to the Docker Host
Overlay Network
Creates a network spanning multiple docker hosts
primarily used when a cluster of Docker hosts are setup in Swarm mode
Macvlan Network
leverage the Linux kernel’s ability to assign multiple
logical addresses based on MAC to a single physical interface
None Network
the container has no Network
Docker Compose
Simplifies creating Containers for different needs
Docker Compose file?
.yml
Docker Compose File Versioning
1
- x
- x
Services
Services is the first root key of the Compose YAML and is the configuration of
the container that needs to be created
build
The build key contains the configuration options that are applied at build time.
context
sets the context to build
image
if present, will build the image and name/tag it
environment/env_file
stores the keys and values for the build
ports
specifies the ports that will be exposed to the port
volumes
adds a named volume to the build
depends_on
pulls dependency requirements
Restart
key that provides the restart policy for the container
By default, set to “no”, never restart
Docker Compose - build
reads the Compose file, scans for build keys
ie
docker-compose build
Docker Compose - down
stops the containers and will proceed to remove containers, volumes, networks dockercompse down(?)
Docker Compose - exec
lets you run ad hoc commands of any containers
Docker Compose - command
docker-compose
