Dockerfile, Docker Image, Docker Container
Let's write a Dockerfile and build a image and run a container.
Dockerfile, Docker Image, Docker Container
Dockerfile, Docker Image, Docker Container
It could be difficult to comprehend all the terms if you are new to Docker. Many Docker terminology can signify various things to different people, and they are occasionally used in diverse contexts. For instance, you could be curious about the differences between a Docker image and a Docker container, much like other people who are learning about Docker. They differ in a modest but important way.
The differences between Docker images and containers, and docker files will be covered in this article, which will also explain how and when to utilize each.
Dockerfile, Docker Image, Docker Container
Write a [Dockerfile]
- A Dockerfile is a file written for the purpose of creating an image in Docker. It can be considered a template that specifies information about the image to be built. After writing a Dockerfile based on various commands and building it, Docker sequentially executes the instructions listed in the Dockerfile to create a Docker image.
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# This refers to the image that will serve as the foundation for the image being created.
# If the image is not available locally, it will be pulled from Docker Hub.
FROM python:3.11-slim
LABEL maintainer="ds2man@example.com"
LABEL version="1.0"
# Install required packages (optimize apt and clean up)
# Execute commands in a new layer and create a new image.
# (Each RUN command creates a single image.)
RUN apt-get update && \
apt-get install -y vim && \
rm -rf /var/lib/apt/lists/*
# Set the working directory first
# Specify the working directory. If the directory does not exist, it will be created.
# Once the working directory is set, all subsequent commands operate relative to this directory
WORKDIR /app
# Create required directories
RUN mkdir -p Common Config
# Set Python environment variable to prevent buffering
# When you want a Python application running inside a Docker container to output logs immediately.
ENV PYTHONUNBUFFERED=1
# Copy only requirements.txt first to leverage Docker cache
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
# Copy the rest of the application files
COPY . /app/
# Set the entry point
ENTRYPOINT ["python", "dockertest_main.py"]
Build a [Docker Image]
- When creating a Docker image, you can enter the following command, and the image build process will start based on the contents of the Dockerfile.
docker build -t {image_name:version} {path_to_dockerfile}
docker build -t ds2man/dockertest:v0.1 .
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(MyDev) jaoneol@DESKTOP-B7GM3C5:~/GP-MyReference/10.MyDockerTest$ docker build -t ds2man/dockertest:v0.1 .
[+] Building 11.5s (14/14) FINISHED docker:default
=> [internal] load build definition from dockerfile 0.0s
=> => transferring dockerfile: 818B 0.0s
=> [internal] load metadata for docker.io/library/python:3.11-slim 1.7s
=> [auth] library/python:pull token for registry-1.docker.io 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [1/8] FROM docker.io/library/python:3.11-slim@sha256:42420f737ba91d509fc60d5ed65ed0492678a90c561e1fa08786ae8ba8b52eda 0.0s
=> [internal] load build context 0.0s
=> => transferring context: 877B 0.0s
=> CACHED [2/8] RUN apt update && apt install -y vim 0.0s
=> CACHED [3/8] RUN mkdir -p /app /app/Common /app/Config 0.0s
=> CACHED [4/8] WORKDIR /app 0.0s
=> [5/8] COPY [*.py, *.txt, ./] 0.0s
=> [6/8] COPY [common/*.py, common/] 0.0s
=> [7/8] COPY [config/*.yml, config/] 0.0s
=> [8/8] RUN pip install -r requirements.txt 9.0s
=> exporting to image 0.6s
=> => exporting layers 0.5s
=> => writing image sha256:d2bf3aae2280c9aaf54db484aefd65f3274c65ca739611b989a12de1febcb489 0.0s
=> => naming to docker.io/ds2man/dockertest:v0.1 0.0s
(MyDev) jaoneol@DESKTOP-B7GM3C5:~/GP-MyReference/10.MyDockerTest$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
ds2man/dockertest v0.1 d2bf3aae2280 36 seconds ago 440MB
(MyDev) jaoneol@DESKTOP-B7GM3C5:~/GP-MyReference/10.MyDockerTest$ su -
Password:
# the location where image layers are stored is `/var/lib/docker/overlay2`.
# This is where Docker's Union File System (OverlayFS) layers are stored.
# For reference, based on the Dockerfile, there should be a total of 6 layers(1 `FROM`, 3 `RUN`, and 2 `COPY`).
# However, it was observed that a total of 13 layers were added.
# Here’s why:
# 1. Docker Uses Additional Metadata Layers
# 2. Multiple Layer IDs for a Single `RUN`
# 3. Cache and Intermediate Layers
# 4. Base Image (Python 3.11-slim) May Have Multiple Layers
The number of directories in **/var/lib/docker/overlay2/** does not always directly correspond to the number of layers in your Docker image. Here’s why:
root@DESKTOP-B7GM3C5:~# cd /var/lib/docker/overlay2
root@DESKTOP-B7GM3C5:/var/lib/docker/overlay2# ls -lrt
total 56
drwx--x--- 3 root root 4096 Feb 10 23:28 x7x9g5ma755hstt5pa9lsesbe
drwx--x--- 3 root root 4096 Feb 10 23:29 uhov30mxr5oouxlwdfeu5vndm
drwx--x--- 3 root root 4096 Feb 10 23:29 q7ej3cmtyuqadsj9g7rsklrpn
drwx--x--- 3 root root 4096 Feb 10 23:29 bba9b62b6e19449cf185100b6435349ea98942de2ff8f30415909d62aadb5cc7
drwx--x--- 4 root root 4096 Feb 10 23:29 1b92b82ac65573f09370464bc93b0494317c67a2e1d53fd39d348e6119d5b153
drwx--x--- 4 root root 4096 Feb 10 23:29 d90cbc202fcbb29ca8558e1d5a8fd601751739eb65939aadf0a217f2f587630d
drwx--x--- 4 root root 4096 Feb 10 23:29 d634bb397fb296e81aa3496e2ca71fb7e84a86e45ca4b135e4b280c08609ad6f
drwx--x--- 4 root root 4096 Feb 10 23:29 yc8cnrxe527q5ity9rsgvtaha
drwx--x--- 4 root root 4096 Feb 10 23:29 rgqlm10jleb879npij8e6iiqh
drwx--x--- 4 root root 4096 Feb 10 23:29 h2tl0wo9rypf4txvet5gq830r
drwx--x--- 4 root root 4096 Feb 10 23:29 st0t93ceil3umbwnl9t0awb4c
drwx------ 2 root root 4096 Feb 10 23:29 l
drwx--x--- 4 root root 4096 Feb 10 23:29 migrpzts9fsudtavuf44z3pd4
drwx--x--- 4 root root 4096 Feb 10 23:29 h0mfkmt88jzso9nbhjyu5mnot
root@DESKTOP-B7GM3C5:/var/lib/docker/overlay2#
- The .dockerignore file specifies which files should be excluded when building an image with a Dockerfile (similar to .gitignore). I configured the .dockerignore file as follows to exclude files unrelated to production when building the image.
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##################
# vi .dockerignore
##################
.gitignore
.dockerignore
.flake8
.env
mytestfile.txt
Run a [Docker Container]
Let’s run the container using the following command.
docker run -d --env-file={environment variable file} --name {container_name} {image_name:version}
docker run -d --env-file=.env --name mydocker ds2man/dockertest:v0.1To access a Docker container and inspect its structure, run the following command.
docker exec -it {container_name} /bin/bash
docker exec -it mydocker /bin/bash
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(MyDev) jaoneol@DESKTOP-B7GM3C5:~/GP-MyReference/10.MyDockerTest$ docker run -d --env-file=.env --name mydocker ds2man/dockertest:v0.1
7a82d4dd52c5e78b14af53a5f28ba0c1b4a5cbdd74a1fb8a8b6ccb9347701381
(MyDev) jaoneol@DESKTOP-B7GM3C5:~/GP-MyReference/10.MyDockerTest$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
0558e84e3e9e ds2man/dockertest:v0.1 "python dockertest_m…" 19 seconds ago Up 18 seconds mydocker
(MyDev) jaoneol@DESKTOP-B7GM3C5:~/GP-MyReference/10.MyDockerTest$
(MyDev) jaoneol@DESKTOP-B7GM3C5:~/GP-MyReference/10.MyDockerTest$ docker exec -it mydocker /bin/bash
root@7a82d4dd52c5:/app# ls
common config dockerfile dockertest_main.py log requirements.txt
root@7a82d4dd52c5:/app#
This post is licensed under CC BY 4.0 by the author.