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Docker Notes: Docker

Docker fileformats

  • FROM

Usage:

FROM <image>
FROM <image>:<tag>
FROM <image>@<digest>

Information:

  • FROM must be the first non-comment instruction in the Dockerfile.
  • FROM can appear multiple times within a single Dockerfile in order to create multiple images. Simply make a note of the last image ID output by the commit before each new FROM command.
  • The tag or digest values are optional. If you omit either of them, the builder assumes a latest by default. The builder returns an error if it cannot match the tag value.

Reference - Best Practices

  • MAINTAINER

Usage:

MAINTAINER <name>

The MAINTAINER instruction allows you to set the Author field of the generated images.

Reference

  • RUN

Usage:

RUN <command> (shell form, the command is run in a shell, which by default is /bin/sh -c on Linux or cmd /S /C on Windows)
RUN ["<executable>", "<param1>", "<param2>"] (exec form)

Information:

The exec form makes it possible to avoid shell string munging, and to RUN commands using a base image that does not contain the specified shell executable.
The default shell for the shell form can be changed using the SHELL command.
Normal shell processing does not occur when using the exec form. For example, RUN ["echo", "$HOME"] will not do variable substitution on $HOME.

Reference - Best Practices

  • CMD

Usage:

CMD ["<executable>","<param1>","<param2>"] (exec form, this is the preferred form)
CMD ["<param1>","<param2>"] (as default parameters to ENTRYPOINT)
CMD <command> <param1> <param2> (shell form)

Information:

The main purpose of a CMD is to provide defaults for an executing container. These defaults can include an executable, or they can omit the executable, in which case you must specify an ENTRYPOINT instruction as well.
There can only be one CMD instruction in a Dockerfile. If you list more than one CMD then only the last CMD will take effect.
If CMD is used to provide default arguments for the ENTRYPOINT instruction, both the CMD and ENTRYPOINT instructions should be specified with the JSON array format.
If the user specifies arguments to docker run then they will override the default specified in CMD.
Normal shell processing does not occur when using the exec form. For example, CMD ["echo", "$HOME"] will not do variable substitution on $HOME.

Reference - Best Practices

  • LABEL

Usage:

LABEL <key>=<value> [<key>=<value> ...]

Information:

The LABEL instruction adds metadata to an image.
To include spaces within a LABEL value, use quotes and backslashes as you would in command-line parsing.
Labels are additive including LABELs in FROM images.
If Docker encounters a label/key that already exists, the new value overrides any previous labels with identical keys.
To view an image’s labels, use the docker inspect command. They will be under the "Labels" JSON attribute.

Reference - Best Practices

EXPOSE

Usage:

EXPOSE <port> [<port> ...]

Information:

Informs Docker that the container listens on the specified network port(s) at runtime.
EXPOSE does not make the ports of the container accessible to the host.

Reference - Best Practices

ENV

Usage:

ENV <key> <value>
ENV <key>=<value> [<key>=<value> ...]

Information:

The ENV instruction sets the environment variable <key> to the value <value>.
The value will be in the environment of all “descendant” Dockerfile commands and can be replaced inline as well.
The environment variables set using ENV will persist when a container is run from the resulting image.
The first form will set a single variable to a value with the entire string after the first space being treated as the <value> - including characters such as spaces and quotes.

Reference - Best Practices

ADD

Usage:

ADD <src> [<src> ...] <dest>
ADD ["<src>", ... "<dest>"] (this form is required for paths containing whitespace)

Information:

Copies new files, directories, or remote file URLs from <src> and adds them to the filesystem of the image at the path <dest>.
<src> may contain wildcards and matching will be done using Go’s filepath.Match rules.
If <src> is a file or directory, then they must be relative to the source directory that is being built (the context of the build).
<dest> is an absolute path, or a path relative to WORKDIR.
If <dest> doesn’t exist, it is created along with all missing directories in its path.

Reference - Best Practices

COPY

Usage:

COPY <src> [<src> ...] <dest>
COPY ["<src>", ... "<dest>"] (this form is required for paths containing whitespace)

Information:

Copies new files or directories from <src> and adds them to the filesystem of the image at the path <dest>.
<src> may contain wildcards and matching will be done using Go’s filepath.Match rules.
<src> must be relative to the source directory that is being built (the context of the build).
<dest> is an absolute path, or a path relative to WORKDIR.
If <dest> doesn’t exist, it is created along with all missing directories in its path.

Reference - Best Practices

ENTRYPOINT

Usage:

ENTRYPOINT ["<executable>", "<param1>", "<param2>"] (exec form, preferred)
ENTRYPOINT <command> <param1> <param2> (shell form)

Information:

Allows you to configure a container that will run as an executable.
Command line arguments to docker run <image> will be appended after all elements in an exec form ENTRYPOINT and will override all elements specified using CMD.
The shell form prevents any CMD or run command line arguments from being used, but the ENTRYPOINT will start via the shell. This means the executable will not be PID 1 nor will it receive UNIX signals. Prepend exec to get around this drawback.
Only the last ENTRYPOINT instruction in the Dockerfile will have an effect.

Reference - Best Practices

VOLUME

Usage:

VOLUME ["<path>", ...]
VOLUME <path> [<path> ...]

Creates a mount point with the specified name and marks it as holding externally mounted volumes from native host or other containers.

Reference - Best Practices

USER

Usage:

USER <username | UID>

The USER instruction sets the user name or UID to use when running the image and for any RUN, CMD and ENTRYPOINT instructions that follow it in the Dockerfile.

Reference - Best Practices

WORKDIR

Usage:

WORKDIR </path/to/workdir>

Information:

Sets the working directory for any RUN, CMD, ENTRYPOINT, COPY, and ADD instructions that follow it.
It can be used multiple times in the one Dockerfile. If a relative path is provided, it will be relative to the path of the previous WORKDIR instruction.

Reference - Best Practices

ARG

Usage:

ARG <name>[=<default value>]

Information:

Defines a variable that users can pass at build-time to the builder with the docker build command using the --build-arg <varname>=<value> flag.
Multiple variables may be defined by specifying ARG multiple times.
It is not recommended to use build-time variables for passing secrets like github keys, user credentials, etc. Build-time variable values are visible to any user of the image with the docker history command.
Environment variables defined using the ENV instruction always override an ARG instruction of the same name.
Docker has a set of predefined ARG variables that you can use without a corresponding ARG instruction in the Dockerfile.
    HTTP_PROXY and http_proxy
    HTTPS_PROXY and https_proxy
    FTP_PROXY and ftp_proxy
    NO_PROXY and no_proxy

Reference

ONBUILD

Usage:

ONBUILD <Dockerfile INSTRUCTION>

Information:

Adds to the image a trigger instruction to be executed at a later time, when the image is used as the base for another build. The trigger will be executed in the context of the downstream build, as if it had been inserted immediately after the FROM instruction in the downstream Dockerfile.
Any build instruction can be registered as a trigger.
Triggers are inherited by the "child" build only. In other words, they are not inherited by "grand-children" builds.
The ONBUILD instruction may not trigger FROM, MAINTAINER, or ONBUILD instructions.

Reference - Best Practices

STOPSIGNAL

Usage:

STOPSIGNAL <signal>

The STOPSIGNAL instruction sets the system call signal that will be sent to the container to exit. This signal can be a valid unsigned number that matches a position in the kernel’s syscall table, for instance 9, or a signal name in the format SIGNAME, for instance SIGKILL.

Reference

HEALTHCHECK

Usage:

HEALTHCHECK [<options>] CMD <command> (check container health by running a command inside the container)
HEALTHCHECK NONE (disable any healthcheck inherited from the base image)

Information:

Tells Docker how to test a container to check that it is still working
Whenever a health check passes, it becomes healthy. After a certain number of consecutive failures, it becomes unhealthy.
The <options> that can appear are...
    --interval=<duration> (default: 30s)
    --timeout=<duration> (default: 30s)
    --retries=<number> (default: 3)
The health check will first run interval seconds after the container is started, and then again interval seconds after each previous check completes. If a single run of the check takes longer than timeout seconds then the check is considered to have failed. It takes retries consecutive failures of the health check for the container to be considered unhealthy.
There can only be one HEALTHCHECK instruction in a Dockerfile. If you list more than one then only the last HEALTHCHECK will take effect.
<command> can be either a shell command or an exec JSON array.
The command's exit status indicates the health status of the container.
    0: success - the container is healthy and ready for use
    1: unhealthy - the container is not working correctly
    2: reserved - do not use this exit code
The first 4096 bytes of stdout and stderr from the <command> are stored and can be queried with docker inspect.
When the health status of a container changes, a health_status event is generated with the new status.

Reference

SHELL

Usage:

SHELL ["<executable>", "<param1>", "<param2>"]

Information:

Allows the default shell used for the shell form of commands to be overridden.
Each SHELL instruction overrides all previous SHELL instructions, and affects all subsequent instructions.
Allows an alternate shell be used such as zsh, csh, tcsh, powershell, and others.

Docker Build & Run Docker

  • Create image using this directory’s Dockerfile

docker build -t image-name .

  • Run “image-name” mapping port 8080 to 80

docker run -p 8080:80 image-name

  • Run “image-name” mapping port 8080 to 80, but in detached mode

docker run -d -p 8080:80 image-name

  • See a list of all running containers

docker ps

  • Gracefully stop the specified container

docker stop <hash>

  • See a list of all containers, even the ones not running

docker ps -a

  • Force shutdown of the specified container

docker kill <hash>

  • Remove the specified container from this machine

docker rm <hash>

  • Remove all containers from this machine

docker rm $(docker ps -a -q)

  • Show all images on this machine

docker images -a

  • LEGACY: Remove the specified image from this machine

docker rmi <imagename>

  • LEGACY:Remove all images from this machine

docker rmi $(docker images -q)

  • LEGACY: Remove all images with dependencies

docker images -q | xargs docker rmi –f

  • Log in this CLI session using your Docker credentials

docker login

  • Tag for upload to registry

docker tag <image> username/repository:tag

  • Upload tagged image to registry

docker push username/repository:tag

  • Run image from a registry

docker run username/repository:tag

  • List Docker volume

docker volume ls

  • List Docker Network

docker network ls

Docker Compose Docker

  • Build Docker Images using Docker Compose file

docker-compose build

  • Run Docker Containers

docker-compose up

  • Run Docker Containers in background Mode

docker-compose up -d

  • Build Images before starting Containers

docker-compose up --build

  • Recreate Containers from existing images

docker-compose up --force-recreate

  • Stop and Remove Containers, Volumes, Networks, and Images

docker-compose down

  • List Containers

docker-compose ps -a

  • Display Log output

docker-compose logs

Docker Swarm Docker

  • Initialize

docker swarm init

  • Join Docker Cluster

```` docker swarm join --token SWMTKN-1-3pu6hszjas19xyp7ghgosyx9k8atbfcr8p2is99znpy26u2lkl-1awxwuwd3z9j1z3puu7rcgdbx <manager/worker>:2377 ```

  • List Docker Nodes in Swarm Cluster

docker node ls

  • List all running applications on this Docker host

docker stack ls

  • Run the specified Compose file

docker stack deploy -c <composefile> <STACK_NAME>

  • List the services associated with an app

docker stack services <appname>

  • List the running containers associated with an app

docker stack ps <appname>

  • Tear down an application

docker stack rm <STACK_NAME>alias dstr='docker stack rm'

  • Docker Swarm Service list

docker service ls alias dsls='docker service ls'

  • List the tasks of one or more services

docker service ps <service_name> alias dsp='docker service ps'

  • Docker Swarm Service logs

alias dsl='docker service logs'

  • Remove specific docker swarm service

alias dsr='docker service rm'

  • Remove unused Containers, Images, Network, etc.

alias sprune='docker system prune'

  • Remove unused Volumes

alias vprune='docker volume prune'

  • Create Secret

docker secret create <SECRET_NAME> <SECRET_PATH>

  • Create Config

docker config create <CONFIG_NAME> <CONFIG_FILE_PATH>