Dockerfile
Dockerfile:
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FROM ubuntu:latest
RUN touch test
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Dockerfile is good to maintenance the build image (rather than docker commit by a container)
Build docker
Build docker: on the directory for the project (with Dockerfile),
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% docker build .
[+] Building 0.7s (6/6) FINISHED
=> [internal] load build definition from Dockerfile 0.1s
=> => transferring dockerfile: 75B 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/ubuntu:latest 0.0s
=> [1/2] FROM docker.io/library/ubuntu:latest 0.0s
=> [2/2] RUN touch test 0.4s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:d6d8116cf6839173dab14b9a5b0bca89ba55230def590630920d41f453da5c40
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Filter dangling image (With “none”)
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$ docker images -f dangling=true
REPOSITORY TAG IMAGE ID CREATED SIZE
<none> <none> d6d8116cf683 50 seconds ago 69.2MB
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Build docker image with name
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$ docker build -t new-ubuntu:latest .
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
new-ubuntu latest 2b9384f7377a 4 seconds ago 69.2MB
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Dockerfile instruction
FROM, RUN, CMD
- FROM: set the image
- RUN : set commands to run and create image layer
- one RUN creates one layer
- CMD : set the default command of the container
- CMD [“executable”, “param1”, “param2”]
- CMD does NOT create a layer
Dockerfile:
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FROM ubuntu:latest
RUN apt-get update && apt-get install -y \
curl \
nginx \
cvs
CMD ["/bin/bash"]
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Build a container
Run container
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docker run 8bedd9090ee8
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Best practice
- Minimize a base image (by FROM)
- Minimize the number of layer (one RUN command aligns to one layer)
- 3 layer : RUN, COPY,ADD
- connect commands by “&&”
- line feed by
\
- Utilize cash effectively
- If already built (RUN command in the docker file), that layer is cashed.
- When creating the docker image, split RUN command for using cash (step by step)
- After completion in docker image building, unify the RUN command at one line.
COPY
Dockerfile:
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FROM ubuntu:latest
RUN mkdir /new_dir
COPY something /new_dir/
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Build and run a container
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$ docker build .
$ docker run -it --rm 8efaf4e1470341 bash
root@46719dea9e21:/# ls /new_dir/
something
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ADD
ADD allows compress large file to .tar file and decompress it on container
Dockerfile:
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FROM ubuntu:latest
ADD compressed.tar /
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Build and run a container. Differently from COPY, ADD decompress the tar file on the container.
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$ docker build .
$ docker run -it --rm 1d6c0226b339925 bash
root@81c520e35e5b:/# ls
bin boot dev etc home lib media mnt opt proc root run sample_folder sbin srv sys tmp usr var
root@81c520e35e5b:/# cd sample_folder/
root@81c520e35e5b:/sample_folder# ls
hello
root@81c520e35e5b:/sample_folder# cat hello
hello
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docker build -f “dockerfile”
Build a container with a Dockerfile which does not exist in the build context
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docker build -f ../Dockerfile.dev .
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ENTRYPOINT
ENTRYPOINT is used when you want to use a container as a command:
- cannot be updated on
docker run
- CMD gets to a list of command parameter; [“param1”, “param2”]
- CMD can be updated on
docker run
Dockerfile:
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FROM ubuntu:latest
RUN touch test
ENTRYPOINT ["ls"]
CMD ["--help"]
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$ docker build .
$ docker run --rm cfb4cd70ef26757fe10d
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.
....
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When updating a parameter,
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$ docker run --rm cfb4cd70ef26757fe10d -1
bin
boot
dev
etc
home
lib
media
mnt
opt
proc
root
run
sbin
srv
sys
test
tmp
usr
var
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ENV
Set environment variables on a container
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ENV <key> <value>
ENV <key>=<value>
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Dockerfile:
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FROM ubuntu:latest
ENV key1 test1
ENV key2=test2
ENV key3=t\ e\ s\ t
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docker build .
docker run -it --rm f3df2f70c5b3 bash
root@dd101e9cbc8f:/# env
HOSTNAME=dd101e9cbc8f
...
key2=test2
key3=t e s t
key1=test1
...
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WORKDIR
In a dfault, RUN command works on root (/) directory in a container.
Dockerfile:
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FROM ubuntu:latest
RUN mkdir sample_folder
WORKDIR /sample_folder
RUN touch sample_file
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Run a container
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% docker run -it --rm e9466222b0bf8e5 bash
root@7d258146df98:/sample_folder# ls
sample_file
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