CentOS Stream 8
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Docker : Use Dockerfile
2021/04/06
 
Use Dockerfile and create Docker images automatically.
It is also useful for configuration management.
[1] For example, Create a Dockerfile that Apache httpd is installed and started.
[root@dlp ~]#
vi Dockerfile
# create new

FROM centos
MAINTAINER ServerWorld <admin@srv.world>

RUN dnf -y install httpd
RUN echo "Dockerfile Test on Aapche httpd" > /var/www/html/index.html

EXPOSE 80
CMD ["-D", "FOREGROUND"]
ENTRYPOINT ["/usr/sbin/httpd"]

# build image ⇒ docker build -t [image name]:[tag] .

[root@dlp ~]#
docker build -t srv.world/centos-httpd:latest ./

Sending build context to Docker daemon  11.26kB
Step 1/7 : FROM centos
 ---> 300e315adb2f
Step 2/7 : MAINTAINER ServerWorld <admin@srv.world>
 ---> Running in 745ea9e6168a
Removing intermediate container 745ea9e6168a
 ---> bff9628ba408
Step 3/7 : RUN dnf -y install httpd
 ---> Running in a7985088ba17
 
.....
.....

Successfully built 83fe1ffbabdb
Successfully tagged srv.world/centos-httpd:latest

[root@dlp ~]#
docker images

REPOSITORY               TAG       IMAGE ID       CREATED          SIZE
srv.world/centos-httpd   latest    83fe1ffbabdb   58 seconds ago   250MB
srv.world/centos-nginx   latest    ae7ab6688f5e   4 minutes ago    289MB
centos                   latest    300e315adb2f   3 months ago     209MB

# run container

[root@dlp ~]#
docker run -d -p 8081:80 srv.world/centos-httpd

c1530e2ae462b20b201891a0e7262b7deb890ce02b85ccf733c4e48b4bc8a78d
[root@dlp ~]#
docker ps

CONTAINER ID   IMAGE                    COMMAND                  CREATED          STATUS         PORTS                  NAMES
c1530e2ae462   srv.world/centos-httpd   "/usr/sbin/httpd -D …"   10 seconds ago   Up 9 seconds   0.0.0.0:8081->80/tcp   thirsty_jones

# verify accesses

[root@dlp ~]#
curl localhost:8081

Dockerfile Test on Aapche httpd
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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