Docker Guide. Keywords: docker

docker_guide.md

DOCKER GUIDE

Docker is a tool that follows the Cattle, no pets DevOps mantra. It describes your hosting environment via a Dockerfile. Each system deployment results in an entirely new reprovisionned hosting environment while the other is decommissioned in the background. Docker achieves this by making it cheap to create new system images to spawn fleets of new containers.

Table of contents

• Quick example recap
• Popular commands
• Key concepts
  • Image vs Container
  • You don't reconfigure containers, instead you reprovision them
  • ENTRYPOINT vs CMD
• Getting started
  • Quick start
  • docker build vs docker run vs docker start vs docker exec
    • Creating an image with docker build
    • Creating a container from an image with docker run
    • Starting an existing container with docker start
    • Executing commands in a running container with docker exec
  • Creating a Dockerfile
• The Dockerfile
  • ARG and ENV
  • ADD and COPY
  • RUN
  • ENTRYPOINT and CMD
    • Basics ENTRYPOINT and CMD
    • CMD vs RUN
    • Overriding them
  • ONBUILD
• Multi-stage builds
  • The old way - aka The Builder Pattern
  • The new way - Out-of-the-box multi-stage build
• Docker configuration
  • Adding other Docker registries
• Development workflow
  • Designing the correct container
  • Logs
• Networking
  • Port binding
• Popular base images
• Tips and tricks
  • Dynamic base image with ARG
• Best practices
  • The instructions order in your Dockerfile matters for performance
  • Keep your docker project small
  • Use a .dockerignore
  • Carefull with single lines RUN commands
  • Avoid downloading resources using ADD
  • Use multi-stage builds instead of single build or the builder pattern
• FAQ
  • How to delete all the containers on my local machine?
  • How to delete all the images on my local machine?
  • How to run a container in the backgound?
  • How to pass variables to the docker build command?
  • How to configure Docker to use other registries?
  • How read or stream a container's logs?
  • How to set the PATH in the Dockerfile?
  • How to create a global ARG in a multi-stage build?
• Annex
  • Simple NodeJS Dockerfile and .dockerignore files
  • Terminal shortcut config
• References

Quick example recap

1. Create a new NodeJS project:

mkdir my-app && \
cd my-app && \
npm init --yes && \
npm i express && \
touch index.js && \
touch Dockerfile

2. Paste the following hello world API in the index.js:

const express = require('express')
const app = express()

app.get('/', (req, res) => {
	res.send('hello world')
})

app.listen(3000, () => console.log(`Server ready and listening on port ${3000}`))

3. Paste the following in the Dockerfile:

# Use the official lightweight Node.js 12 image.
# https://hub.docker.com/_/node
FROM node:12-slim

# Create and change to the app directory.
WORKDIR /usr/src/app

# Copy application dependency manifests to the container image.
# A wildcard is used to ensure both package.json AND package-lock.json are copied.
# Copying this separately prevents re-running npm install on every code change.
COPY package*.json ./

# Install production dependencies.
RUN npm install --only=prod

# Copy local code to the container image.
COPY . ./

# Run the web service on container startup.
CMD ["node", "index.js"]

4. Build an image for this project:

docker build -t nodejs:v0 .

Where:

• -t is the tag option which allows to name the image, aka tag the image.
• <IMAGE NAME>:<VERSION TAG> is the usual image naming convention, but you can change it to whatever you prefer.
• . means the current directory to build the image.

5. Launch a new container:

docker run -p 127.0.0.1:4000:3000 nodejs:v0

This last command port-forward the traffic received on 127.0.0.1:4000 to the port 3000 inside the container.

Popular commands

Command	Description
docker image ls	List all images.
docker ps -a	List all containers. The -a options includes the non-running containers.
docker build -t my_image:v1 .	Creates an image from a Dockerfile

Key concepts

Image vs Container

A running instance of an image is called container. An image is made of a set of layers. If you start an image, you have a running container for that image. You can have many running containers of the same image.

You can see all your images with docker images whereas you can see your running containers with docker ps -a.

You don't reconfigure containers, instead you reprovision them

A typical newbie scratch head is to wonder how to change the container's config after it has been started. The answer is you can't. For example, if a container with an app listening on port 3000 has been provisioned as follow:

docker run my_image:v1

The app in this container is listening on port 3000. It cannot receive traffic from outside because no port binding has been configured. It is not possible to change that container later. Instead, recreate a new container from that image as follow, and delete the previous container:

docker -p 127.0.0.1:3000:3000 run my_image:v1

Which means, port-forward traffic on 127.0.0.1:3000 to this container on its internal port 3000.

This approach highlights the typicall way of thinking with Docker. Because containers and images are cheap to create, you do not reconfigure them. Instead, you recreate them from scratch. That the DevOps Cattle, no pets mantra.

ENTRYPOINT vs CMD

Demystifying ENTRYPOINT and CMD in Docker

You define those 2 properties in the Dockerfile. For example:

ENTRYPOINT ["echo”, "Hello"]
CMD ["World"]

With those 2 setup, starting a container with docker run <YOUR-IMAGE> will execute the default command echo Hello World. As you can see, the default command is just the concatenation of the entrypoint and the cmd.

Though those 2 can be strings, eventually, docker converts them to arrays, so it's usually less confusing to always use arrays.

To learn more about this topic, please refer to the ENTRYPOINT and CMD section.

Getting started

Quick start

• Install Docker
• Make sure it runs (launch the app on your Desktop. Not sure how to launch it from the terminal). If it is not launched (i.e., the daemon is not started in the background, the docker command will fail).
• Create a Dockerfile.
• Build the image: docker build -t <IMAGE NAME>:<VERSION TAG> .

Where:

• -t is the tag option which allows to name the image, aka tag the image.
• <IMAGE NAME>:<VERSION TAG> is the usual image naming convention, but you can change it to whatever you prefer.
• . means the current directory to build the image.

• List your containers: docker ps -a
• Launch your container: docker start -a <MY-CONTAINER-NAME>

docker build vs docker run vs docker start vs docker exec

This section explains the important differences between:

• Creating an image with docker build
• Creating a container from an image with docker run
• Starting an existing container with docker start
• Executing commands in a running container with docker exec

If you're still confused by the conceptual difference between an image and a container, please refer to the Image vs Container section.

Creating an image with docker build

Typical usage: docker build -t my_image:v1 . Where:

• -t is the tag option which allows to name the image, aka tag the image.
• my_image:v1 is the usual image naming convention, but you can change it to whatever you prefer.
• . means the current directory to build the image.

1. If your project does not contain a Dockerfile and a .dockerignore, create one. Typically, the Dockerfile imports the project's file you need into the image and defines a command that can start your project, or an entry point that allows to call your project's APIs.
2. Create the image for your project with docker build -t <IMAGE NAME>:<VERSION TAG> . (e.g., docker build -t my-website:v1 .).
3. Once that's done, you can see your image with docker images.
4. To delete your image, run docker rmi <IMAGE ID>

Creating a container from an image with docker run

Typical usage: docker run -it my_image:v1 Where -it allows to interact with the container's STDIN (-i) via the terminal (-t).

Once you have an image on your local machine, you can start a container with docker run <IMAGE_ID|IMAGE_NAME:IMAGE_TAG>. To list the available images and their IDs, use docker images.

Each time you use docker run <IMAGE ID>, a new container is created and started. To test this command, run it multiple times and then execute docker ps -a. You should see mutliple container for that specific image ID.

To delete the containers you don't need, run docker rm <CONTAINER ID>.

Tips:

• Use docker run -it <IMAGE ID> if you need to interact with that container directly via the terminal (-i means STDIN and -t means terminal).

Starting an existing container with docker start

Use docker start if you simply want to start an existing container instead of creating a new one from the image.

1. List all the containers:

docker ps -a

2. You can start any container using either its CONTAINER ID or its NAMES:

docker start tender_bassi

Executing commands in a running container with docker exec

This command allows to execute a command inside a running container. The most common use of it is to open a shell terminal in a container to start interacting with that container:

docker exec -it <CONTAINER ID> sh

Creating a Dockerfile

# Use the official lightweight Node.js 12 image.
# https://hub.docker.com/_/node
FROM node:12-slim

# Create and change to the app directory.
WORKDIR /usr/src/app

# Copy application dependency manifests to the container image.
# A wildcard is used to ensure both package.json AND package-lock.json are copied.
# Copying this separately prevents re-running npm install on every code change.
COPY package*.json ./

# Install production dependencies.
RUN npm install --only=prod

# Configure Nuxt with the host, otherwise, it won't be reachable from outside Docker
ENV NUXT_HOST=0.0.0.0

# Copy local code to the container image.
COPY . ./

# Run the web service on container startup.
CMD npm start

IMPORTANT: The instructions order affects the speed at which Docker can create/recreate the image. More details about this topic in the The instructions order in your Dockerfile matters for performance section.

The Dockerfile

IMPORTANT: The instructions order in your Dockerfile matters for performance

Example:

# Comments can be used using the hashtag symbol
# Always start with FROM. This specify the base image
FROM ubuntu:14.04
# MAINTAINER is not required, but that’s a good practice
MAINTAINER Nicolas Dao <nicolas.dao@gmail.com>
# Creates a new environment variable called myName
ENV myName John Doe
# Add all the files and folders from your docker project into your image under /app/src
ADD . /app/src
# Add all the files and folders from your docker project into your image under /app/src2. To 
# understand the difference between COPY and ADD jump to the next ADD vs COPY section
COPY . /app/src2
# Create a new data volume in your image. More info about data volume here.
VOLUME /new-data-volume
# By default, RUN uses /bin/sh. The following line is pretty easy to understand. More info here
RUN apt-get update && apt-get install -y ruby ruby-dev
# WORKDIR set up the working directory for RUN, CMD, ENTRYPOINT, COPY, and ADD. Each time you run, 
# it will be relative to the previous working directory(unless you specify an absolute path).
# If you use a directory which does not exist, that directory will be automatically created.  
WORKDIR /a # Create a new ‘a’ directory at the container’s root, and set it up as the working dir.
RUN pwd    # /a
WORKDIR b  # Create a new ‘b’ directory under ‘a’, and set it up as the working dir.
RUN pwd    # /a/b
# ONBUILD is typically used in image intended to be used as base image. More details here
ONBUILD ADD . /app/src 
# CMD is the command that will be run after your container has started. More info here
CMD["echo", "Hello world" ]

ARG and ENV

The following Dockerfile defines a MSG argument and a HELLO environment variable:

FROM amazon/aws-lambda-nodejs:12
ARG MSG
ENV HELLO Hello ${MSG}

HELLO is an environment variable accessible in all the systems running inside the container defined by this image. It is set to the text message Hello ${MSG} where MSG is an argument that can be set via the docker build command:

docker build --build-arg MSG="Mike Davis" -t my-app

If you have multiple arguments:

docker build --build-arg MSG="Mike Davis" --build-arg AGE=40 -t my-app

If you need to set a default value for the ARG:

FROM amazon/aws-lambda-nodejs:12
ARG MSG=Baby
ENV HELLO Hello ${MSG}

ARG can also be nested:

FROM amazon/aws-lambda-nodejs:12
ARG MSG=Baby
ARG COOLMSG="you hot ${MSG}"

RUN echo ${COOLMSG}

ADD and COPY

Both exposes the same API: ADD|COPY <src> <dest. in the image>. The difference is that ADD supports more use cases, where COPY only supports sources accessible from your docker project.

ADD supports those following useful use cases:

• src can be a URI
• src can be a tar file. If the compression format is recognized, then the tar file will be automatically unpacked.

The best practice is to use COPY when possible. This is more transparent and obvious for anybody reading the Dockerfile.

RUN

RUN allows you to customize your base image with additional configurations or artifacts. Each time RUN is executed, a new docker commit is performed. When docker is done with the build, you’ll be able that there are a commit for each RUN command.

Run can be use in 2 different ways:

• Shell form: RUN <shell command>
• Exec form: RUN ["executable", "param1", "param2", ... "paramN"], which will result in the following shell command: executable param1 param2 ... paramN

In reality, the shell form is just a shortcut for the following exec form: RUN ["/bin/sh", "-c", "shell command"].

WARNING: The exec form does not invoke a command shell(have no clue on what it invokes instead!!!). That means that exec form does not support variable substitution out-of-the box. If you need variable substitution while using the exec form, you’ll have to explicitly use the shell exec:

RUN ["echo", "$HOME"] # output: $HOME
RUN ["/bin/sh", "-c", "echo", "$HOME"] # output: /users/you/

RUN uses a cache which is not automatically flushed between builds. To explicitly refresh that cache, use the following command:

docker build --no-cache ...

Each RUN will create a new layer. The best practice is to try to keep layers to a minimum. Please refer to the Carefull with single lines RUN commands section to learn more.

ENTRYPOINT and CMD

Basics ENTRYPOINT and CMD

Demystifying ENTRYPOINT and CMD in Docker

You define those 2 properties in the Dockerfile. For example:

ENTRYPOINT ["echo”, "Hello"]
CMD ["World"]

With those 2 setup, starting a container with docker run <YOUR-IMAGE> will execute the default command echo Hello World. As you can see, the default command is just the concatenation of the entrypoint and the cmd.

Though those 2 can be strings, eventually, docker converts them to arrays, so it's usually less confusing to always use arrays.

ENTRYPOINT also work with scripts:

COPY ./docker-entrypoint.sh /
ENTRYPOINT ["/docker-entrypoint.sh"]

CMD vs RUN

• The main difference between CMD and RUN is that CMD does not result in a docker commit. CMD’s purpose is not to modify the base image, but instead to execute a command as soon as the container is up.
• There can only be one CMD per Dockerfile. If there are more than one, only the last one will be executed.

Overriding them

To override CMD:

docker run <IMAGE> Baby

This will print: Hello Baby

To override ENTRYPOINT:

docker run -it --entrypoint /bin/bash <IMAGE>

This will allow to interact with the shell from inside the container.

ONBUILD

This directive allows to execute other directive at image build time. This is usefull when building images based on other images. For example, let's image the following parent image called parentimage:0.0.1:

FROM ubuntu:14.04
...
ONBUILD ADD . /app/src
...

The following child image does not worry about copying its content to /app/src:

FROM parentimage:0.0.1
...

If the parent had been defined as follow:

FROM ubuntu:14.04
...
ADD . /app/src
...

This would have means that the content of the parent would had been added to /app/src.

Multi-stage builds

Original article: https://docs.docker.com/develop/develop-images/multistage-build/

The old way - aka The Builder Pattern

Complex images require more layers to be built. Those additional layers increase the size of the final image, which impact performance. To keep the final image as slim as possible, the first popular pattern called the builder pattern used a shell script that would run two Dockerfile sequentially. The fist one called Dockerfile.build would build all the artefacts similarly to a build server. The image created by this Dockerfile.build would not matter. The artefact would then be passed to the production Dockerfile, which would therefore be lean.

Later, Docker shipped a new feature called multi-stage build.

The new way - Out-of-the-box multi-stage build

Let's imagine we want to package some NodeJS code to inject those files in another image. We don't really care about NodeJS or NPM, we only want the artefact. The following Dockerfile uses a minimal node image to build our project:

FROM node:14-slim
ARG FUNCTION_DIR="/opt/nodejs/"

RUN mkdir -p $FUNCTION_DIR
WORKDIR $FUNCTION_DIR

COPY package*.json ./
RUN npm i --only=prod

ENTRYPOINT ["/bin/sh"]

However, this image is still 168MB. Because we only care about the actual files, we can simply build the smallest image possible and pass it the built artefacts using the multi-stage build API:

FROM node:14-slim AS builder
ARG FUNCTION_DIR="/opt/nodejs/"

RUN mkdir -p $FUNCTION_DIR
WORKDIR $FUNCTION_DIR

COPY package*.json ./
RUN npm i --only=prod

FROM busybox
ARG FUNCTION_DIR="/opt/nodejs/"

RUN mkdir -p $FUNCTION_DIR
WORKDIR $FUNCTION_DIR

COPY --from=builder $FUNCTION_DIR ./

ENTRYPOINT ["/bin/sh"]

The image's size is now 1.8MB.

Docker configuration

The Docker configuration is maintained in the ~/.docker/config.json file.

Adding other Docker registries

By default, deploying new images targets Docker Hub, but you may want to deploy your images using other services (e.g., Google Cloud Container Register or AWS Elastic Container Registry (ECR)).

To add new registries, edit the ~/.docker/config.json file by adding a new credHelpers property as follow:

{
  "credHelpers": {
    "gcr.io": "gcloud",
    "us.gcr.io": "gcloud",
    "eu.gcr.io": "gcloud",
    "asia.gcr.io": "gcloud",
    "staging-k8s.gcr.io": "gcloud",
    "marketplace.gcr.io": "gcloud"
  }
}

Where each key represents a domain (e.g., gcr.io) and each value represents a program (e.g.,gcloud). The above example shows the exhaustive config for setting up Google Cloud Container Registry for the GCloud CLI.

Development workflow

Designing the correct container

As a matter of fact, designing the right container is about designing the right image. Docker excels at creating new images and spawning containers from them in milliseconds. This efficiency comes from its layers design. The original layers take time to be pulled from the registry (e.g., the first time you pull a linux distro preconfigured with NodeJS). But once those layers have been pulled, they are cached on your local system. As you're building your own layers locally, those layers are also cached, and that's why iterating throught building the image you need is so cheap. To test the image, you spawn a container from it. If the container needs to be fixed, you fix the underlying image definition (usually via its Dockerfile) generate a new image, spawn a new container. These are the basics behind the iteration process. You eventually end up with a lot of trash in your Docker images and containers. Simply delete them once you're done.

The iteration process is similar to this:

1. Create a Dockerfile (and a new .dockerignore) based on what you think you need.
2. Create a new image from that Dockerfile as follow: docker build -t <YOUR-IMAGE-NAME>:<YOUR-TAG> .
3. Create a new container from that new image: docker run -it <YOUR-IMAGE-NAME>:<YOUR-TAG>
4. Start interacting with your running container: docker exec -it <CONTAINER ID> sh
5. Iterate though that process until you have the container you want.

Logs

To print the container's logs:

docker logs <CONTAINER ID OR NAME>

Thie issue with this command is that its a one off. If you need to stream the logs continuously, use thos instead:

docker logs --follow <CONTAINER ID OR NAME>

Networking

Port binding

If you package an app in your container that listens on port 3000, and if you intend to expose that app outside of the container, then the following won't work:

docker run my_image:v1

Instead, you need to configure your container with port binding as follow:

docker -p 127.0.0.1:3100:3000 run my_image:v1

The above creates a container configure on the host to do port forwarding so that all traffic sent to the host on 127.0.0.1:3100 is forwarded to the container on its app listening on port 3000.

NOTE: -p stands for publish

Popular base images

Image	Description	Link
scratch	Most minimal image usefull to build other images. It's pretty much the base image for all the others.	https://hub.docker.com/_/scratch
busybox	Minimal image with many UNIX tools preinstalled.	https://hub.docker.com/_/busybox
alpine:<VERSION>	Built on top of busybox, it is a very mininal Linux version.	https://hub.docker.com/_/alpine
node:<version>	Self-explanatory.	https://hub.docker.com/_/node
node:<version>-alpine	Same as node:<version> but with alpine as the base image to save on space. Might not work in all scenarios.	https://hub.docker.com/_/node

Tips and tricks

Dynamic base image with ARG

The following example show how to use a LAYER_01 argument to load different layer image for an AWS Lambda image.

ARG LAYER_01
FROM $LAYER_01 AS layer01
FROM amazon/aws-lambda-nodejs:12
ARG FUNCTION_DIR="/var/task"
ARG LAYER01_PATH="/opt/layer01/"

# Copy layer01 files into the opt/ folder
COPY --from=layer01 /opt/nodejs/ $LAYER01_PATH
ENV NODE_PATH "${LAYER01_PATH}node_modules:${NODE_PATH}"

# Create function directory
RUN mkdir -p ${FUNCTION_DIR}

# Copy handler function and package.json
COPY index.js ${FUNCTION_DIR}

# Set the CMD to your handler (could also be done as a parameter override outside of the Dockerfile)
CMD [ "index.handler" ]

Best practices

The instructions order in your Dockerfile matters for performance

BAD EXAMPLE:

FROM node:12-slim
WORKDIR /usr/src/app
COPY . ./
RUN npm install --only=prod
CMD npm start

GOOD EXAMPLE:

FROM node:12-slim
WORKDIR /usr/src/app
COPY package*.json ./
RUN npm install --only=prod
COPY . ./
CMD npm start

All instructions in your Dockerfile create a new layer(1). Because layers are cached, and because a change to a layer forces the regeneration of all its following layers, it is recommended to start the Dockerfile with the instructions that rarely change. In the GOOD EXAMPLE, the first 4 lines should rarely change(2), while the 5th line (COPY . ./) almost always change. Indeed, each time a file changes, Docker will consider the COPY . ./ as different, which will force the regenaration of all the following instructions. In the BAD EXAMPLE, this includes RUN npm install --only=prod. This is a waste as the dependencies of a NodeJS project rarely change (for the readers unfamiliar with NodeJS, those dependencies are explicitly defined in the package.json and package-lock.json files). A better approach is to rewrite the Dockerfile as follow:

• (1) Only RUN, COPY and ADD generate layers that impact the image size. The other instructions are called intermediate layers.
• (2) Dockers uses the following criteria to determine whether to re-use a cached layer or not:
  • COPY and ADD:
    • When the command has changed;
    • or when the content of the files copied has changed. Docker computes a hash of each file and uses that hash to determine if a file has changed.
  • RUN only check the command. If the command has changed, the layer is regenerated. IMPORTANT: This means that if you must regenerate a RUN layer, you must make sure that it is preceded by an ADD or COPY layer that has changed to.

Keep your docker project small

Small means both bytes and numbers of files. All files in your project will be sent to the Docker daemon at build-time. If there are too many files, or if they are too big, you’ll experience bad performances. If you do have a lot of files, but some of them are not required by the build process, do use a .dockerignore file.

Use a .dockerignore

If files are not part of the build process.

Carefull with single lines RUN commands

Never write RUN apt-get update on its own on a single line, otherwise, Docker will cache that resulting image, and no updates will ever be performed. Instead, use the following:

RUN apt-get update && apt-get install -y s3cmd=1.1.0.*

This is better because:

• Add or remove dependencies explicitly automatically invalidates the cache.
• Now the s3cmd's version is explicit, updating it will force Docker to update the cache.

It's also considered a best practice to organize your dependencies using multi-lines and alphabetical order:

RUN apt-get update && apt-get install -y \ 
    aufs-tools \ 
    automake \ 
    btrfs-tools \ 
    build-essential \ 
    curl \
    s3cmd=1.1.0.*

Avoid downloading resources using ADD

Replace this:

ADD http://example.com/big.tar.xz /usr/src/things/
RUN tar -xJf /usr/src/things/big.tar.xz -C /usr/src/things
RUN make -C /usr/src/things all

With this:

RUN mkdir -p /usr/src/things \
    && curl -SL http://example.com/big.tar.gz \
    | tar -xJC /usr/src/things \
    && make -C /usr/src/things all

The second example is better than the first because the first creates a layer just for the ADD and keep the downloaded resources in the image for no reason.

Use multi-stage builds instead of single build or the builder pattern

Multi-stage builds allows to load all the tools and run all the expensive steps in other intermediate images and then load the final artefacts into a minimal image (small base image and minimal amount of layers). To learn more, please refer to the Multi-stage builds section.

FAQ

How to delete all the containers on my local machine?

docker stop $(docker ps -a -q)
docker rm $(docker ps -a -q)

How to delete all the images on my local machine?

docker stop $(docker ps -a -q)
docker rm $(docker ps -a -q)
docker rmi $(docker images -a -q) --force

How to run a container in the backgound?

This is called detached mode:

docker run -d my_image:v1

How to pass variables to the docker build command?

1. Use the --build-arg option as follow:

docker build --build-arg HTTP_PROXY=http://10.20.30.2:1234 --build-arg FTP_PROXY=http://40.50.60.5:4567 .

2. In your Dockerfile, just after the FROM, add the following commands:

ARG HTTP_PROXY
ARG FTP_PROXY

How to configure Docker to use other registries?

Please refer to the Adding other Docker registries section.

How read or stream a container's logs?

Please refer to the Logs section.

How to set the PATH in the Dockerfile?

ENV PATH="/opt/gtk/bin:${PATH}"

How to create a global ARG in a multi-stage build?

ARG are scoped per build stage. This means that each build stage MUST explicitly define its own ARG. For example, the following is incorrect:

ARG PULUMI_BIN="/opt/.pulumi/bin"

FROM alpine:3.14 AS builder
RUN mkdir -p $PULUMI_BIN

FROM busybox
RUN mkdir -p $PULUMI_BIN

The correct version is:

ARG PULUMI_BIN="/opt/.pulumi/bin"

FROM alpine:3.14 AS builder
ARG PULUMI_BIN
RUN mkdir -p $PULUMI_BIN

FROM busybox
ARG PULUMI_BIN
RUN mkdir -p $PULUMI_BIN

NOTE: Both block will use the same value.

Annex

Simple NodeJS Dockerfile and .dockerignore files

Dockerfile

# Use the official lightweight Node.js 12 image.
# https://hub.docker.com/_/node
FROM node:12-slim

# Create and change to the app directory.
WORKDIR /usr/src/app

# Copy application dependency manifests to the container image.
# A wildcard is used to ensure both package.json AND package-lock.json are copied.
# Copying this separately prevents re-running npm install on every code change.
COPY package*.json ./

# Install production dependencies.
RUN npm install --only=prod

# Copy local code to the container image.
COPY . ./

# Run the web service on container startup.
CMD npm start

.dockerignore

Dockerfile
README.md
node_modules
npm-debug.log

Terminal shortcut config

The following config in your terminal config allows to use:

• d instead of docker.
• drm to delete all the containers.
• drmi to delete all the images.
• dhost 4000:8080 to build an image and launch a container and redirect traffic on 127.0.0.1:4000 to port 8080 in your container.
• dit to build an image and launch a container and start a terminal in it.
• dit --entrypoint /bin/bash to force starting bash.
• dlocal 3000:3100 [other options] instead of docker run -p 127.0.0.1:3000:3100 [other options]

alias d="docker"
function drm() {
	docker stop $(docker ps -a -q) 
	docker rm $(docker ps -a -q)
}
function drmi() {
	docker stop $(docker ps -a -q)
	docker rm $(docker ps -a -q)
	docker rmi $(docker images -a -q) --force
}
function dlocal() {
	docker run -p 127.0.0.1:$1 $2 $3 $4 $5 $6
}
function dhost() {
	docker build -t localapp .
	docker run -p 127.0.0.1:$1 localapp:latest
}
function dit() {
	docker build -t localapp .
	docker run -it $1 $2 $3 localapp:latest
}

References

• Best practices for writing Dockerfiles
• Docker RUN vs CMD vs ENTRYPOINT