Creating Images With Dockerfiles

A common workflow with docker is to first build an image and then run a container from the image.
A container is an "instance" of the image. Several running containers can be going based on the same image.
Docker docs explain what an image is:
"An image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime. An image typically contains a union of layered filesystems stacked on top of each other."
Images can be things like

• an instance of a Debian running nodeJS hosting a rest api
• an instance of alpine running an nginx server

DockerFile

Docker reads a dockerfile as a set of instructions on building an image. Each line is an instruction, a part of the file's "proceedure".

Make one

make a directory & create a dockerfile:

mkdir container-v1
cd container-v1

make the Dockerfile

touch Dockerfile

Prep the file

the dockerfile represents a series of instructions that the os runs. Each line or "section" in the dockerfile is an instruction that Docker uses to prep an image.

# get the node container from dockerHub
FROM node:18

# do something when it starts up
# give it a command to run with **CMD** and an arr of comman args
# `node -e console.log("hey now")` would convert to 
# `["node","-e","console.log(\"hey now\")"]`

CMD ["node", "-e", "console.log(\"omg hi lol\")"]

Without all the comments, the file is a slim 2 line file:

FROM node:18
CMD ["node", "-e", "console.log(\"omg hi lol\")"]

build the image

build the docker image. Here, docker reads the dockerfile and its instructions and build an image.

docker build .
# ...should spit out stats that it is building the image, including image name and a hash of the image


### run the container
docker run -it <container-hash>

the container can also build using a friendly name, a tag

docker build --tag friendly-name-here .

just tagged the container as friendly-name-here!