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Docker : Use Dockerfile
2019/01/22
 
Use Dockerfile and create Docker images automatically.
It is also useful for configuration management.
[1] For example, Create a Dockerfile to install httpd and sshd and also install Supervisor to control multiple services on a Container.
dlp:~ #
vi Dockerfile
# create new

FROM fedora
MAINTAINER ServerWorld <admin@srv.world>

RUN dnf -y install openssh-server httpd supervisor
RUN echo "Hello DockerFile World" > /var/www/html/index.html
RUN mkdir /root/.ssh; chown root. /root/.ssh; chmod 700 /root/.ssh
RUN ssh-keygen -A

ADD supervisord.conf /etc/supervisord.conf
ADD .ssh/id_rsa.pub /root/.ssh/authorized_keys

EXPOSE 22 80
CMD ["/usr/bin/supervisord"]

# create a Supervisor template

dlp:~ #
vi supervisord.conf
[supervisord]
nodaemon=true

[program:sshd]
command=/usr/sbin/sshd -D
autostart=true
autorestart=true

[program:httpd]
command=/usr/sbin/httpd -D FOREGROUND
autostart=true
autorestart=true

# generate SSH key

dlp:~ #
ssh-keygen -q -N "" -f /root/.ssh/id_rsa
# build image ⇒ docker build -t [image name]:[tag] .

dlp:~ #
docker build -t web_server:latest .

Sending build context to Docker daemon 15.87 kB
Step 1/10 : FROM fedora
 ---> 26ffec5b4a8a
Step 2/10 : MAINTAINER ServerWorld <admin@srv.world>
 ---> Running in 4701e055a121
 ---> f366bb5fd2ba
Removing intermediate container f82198c58db8
Step 3/10 : RUN dnf -y install openssh-server httpd supervisor
 ---> Running in 1b27371bf4c2
.....
.....
Successfully built 3fc464a24f9a
Successfully tagged web_server:latest

dlp:~ #
docker images

REPOSITORY               TAG                 IMAGE ID            CREATED             SIZE
web_server               latest              3fc464a24f9a        3 minutes ago       549MB
srv.world/fedora_httpd   latest              5b6251fe21ea        10 minutes ago      499MB
fedora                   latest              26ffec5b4a8a        5 days ago          274MB

# run Container on background

dlp:~ #
docker run -d -p 2022:22 -p 8081:80 web_server

ad51a5c4d0f7db8c1a4669da162410e18f7bf07f891c54f5057cbdd9c0383144

dlp:~ #
docker ps

CONTAINER ID   IMAGE       COMMAND                  CREATED          STATUS         PORTS                                        NAMES
ad51a5c4d0f7   web_server  "/usr/bin/supervisord"   16 seconds ago   Up 15 seconds  0.0.0.0:2022->22/tcp, 0.0.0.0:8081->80/tcp   elastic_davinci

# verify accesses

dlp:~ #
curl localhost:8081

Hello DockerFile World
dlp:~ #
ssh -p 2022 localhost

[root@ad51a5c4d0f7 ~]#
The format of Dockerfile is [INSTRUCTION arguments] .
Refer to the following description for INSTRUCTION.
INSTRUCTION Description
FROM iIt sets the Base Image for subsequent instructions.
MAINTAINER It sets the Author field of the generated images.
RUN It will execute any commands when Docker image will be created.
CMD It will execute any commands when Docker container will be executed.
ENTRYPOINT It will execute any commands when Docker container will be executed.
LABEL It adds metadata to an image.
EXPOSE It informs Docker that the container will listen on the specified network ports at runtime.
ENV It sets the environment variable.
ADD It copies new files, directories or remote file URLs.
COPY It copies new files or directories.
The differences of [ADD] are that it's impossible to specify remore URL and also it will not extract archive files automatically.
VOLUME It creates a mount point with the specified name and marks it as holding externally mounted volumes from native host or other containers
USER It sets the user name or UID.
WORKDIR It sets the working directory.

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