What is dockerfile ?
A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using docker build users can create an automated build that executes several command-line instructions in succession.
Keywords Of Dockerfile :-
There are certain keywords of dockerfile which can be used in to build a specific image.
LABEL : Allows you to add a label to your docker image.
WORKDIR : Set the path from where you want to execute the command defined with CMD.
USER : Set the UID which is to run the container.
RUN : Central executing directive for Dockerfiles.
MAINTAINER : It defines an email address and name of image creator.
FROM : It defines the base image used to start the build process.
CMD : This can be used to execute a command within a container.
VOLUME : The VOLUME command is used to enable access from your container to a directory on the host machine.
ADD : The ADD command gets two arguments: a source and a destination. It basically copies the files from the source on the host into the container’s own filesystem at the set destination.
Lets create a Dockerfile to build a Centos Image.
Create a new directory called dockercentos and :
[root@siddhesh ~]# mkdir dockercentos
[root@siddhesh ~]# cd dockercentos
[root@siddhesh ~]# cat Dockerfile
FROM centos:7
MAINTAINER Siddhesh Kadam siddhesh@tecgeek.info
RUN yum makecache
RUN yum install -y httpd
RUN mkdir -p /etc/mail
RUN mkdir -p /tmp/siddhesh
[root@siddhesh ~]#Save and close the file. Build the image with the command:
[root@siddhesh ~]# docker build -t "apache_centos:DockerFile" .
Sending build context to Docker daemon 2.048kB
Step 1/6 : FROM centos:7
7: Pulling from library/centos
ab5ef0e58194: Pull complete
Digest: sha256:4a701376d03f6b39b8c2a8f4a8e499441b0d567f9ab9d58e4991de4472fb813c
Status: Downloaded newer image for centos:7
---> 5e35e350aded
Step 2/6 : MAINTAINER Siddhesh Kadam siddhesh@tecgeek.info
---> Running in fd4a5a2ccf3d
Removing intermediate container fd4a5a2ccf3d
---> f9ed312db9f8
Step 3/6 : RUN yum makecache
---> Running in 95b113334406
Loaded plugins: fastestmirror, ovl
Determining fastest mirrors
* base: mirror.ash.fastserv.com
* extras: mirror.rackspace.com
* updates: mirror.umd.edu
Metadata Cache Created
Removing intermediate container 95b113334406
---> 6ea4e4f5188b
Step 4/6 : RUN yum install -y httpd
---> Running in 9ef4c5080415
Loaded plugins: fastestmirror, ovl
Loading mirror speeds from cached hostfile
* base: mirror.ash.fastserv.com
* extras: mirror.rackspace.com
* updates: mirror.umd.edu
Resolving Dependencies
--> Running transaction check
---> Package httpd.x86_64 0:2.4.6-90.el7.centos will be installed
--> Processing Dependency: httpd-tools = 2.4.6-90.el7.centos for package: httpd-2.4.6-90.el7.centos.x86_64
--> Processing Dependency: system-logos >= 7.92.1-1 for package: httpd-2.4.6-90.el7.centos.x86_64
--> Processing Dependency: /etc/mime.types for package: httpd-2.4.6-90.el7.centos.x86_64
--> Processing Dependency: libaprutil-1.so.0()(64bit) for package: httpd-2.4.6-90.el7.centos.x86_64
--> Processing Dependency: libapr-1.so.0()(64bit) for package: httpd-2.4.6-90.el7.centos.x86_64
--> Running transaction check
---> Package apr.x86_64 0:1.4.8-5.el7 will be installed
---> Package apr-util.x86_64 0:1.5.2-6.el7 will be installed
---> Package centos-logos.noarch 0:70.0.6-3.el7.centos will be installed
---> Package httpd-tools.x86_64 0:2.4.6-90.el7.centos will be installed
---> Package mailcap.noarch 0:2.1.41-2.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
httpd x86_64 2.4.6-90.el7.centos base 2.7 M
Installing for dependencies:
apr x86_64 1.4.8-5.el7 base 103 k
apr-util x86_64 1.5.2-6.el7 base 92 k
centos-logos noarch 70.0.6-3.el7.centos base 21 M
httpd-tools x86_64 2.4.6-90.el7.centos base 91 k
mailcap noarch 2.1.41-2.el7 base 31 k
Transaction Summary
================================================================================
Install 1 Package (+5 Dependent packages)
Total download size: 24 M
Installed size: 31 M
Downloading packages:
warning: /var/cache/yum/x86_64/7/base/packages/apr-util-1.5.2-6.el7.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID f4a80eb5: NOKEY
Public key for apr-util-1.5.2-6.el7.x86_64.rpm is not installed
--------------------------------------------------------------------------------
Total 40 MB/s | 24 MB 00:00
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
Importing GPG key 0xF4A80EB5:
Userid : "CentOS-7 Key (CentOS 7 Official Signing Key) <security@centos.org>"
Fingerprint: 6341 ab27 53d7 8a78 a7c2 7bb1 24c6 a8a7 f4a8 0eb5
Package : centos-release-7-7.1908.0.el7.centos.x86_64 (@CentOS)
From : /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : apr-1.4.8-5.el7.x86_64 1/6
Installing : apr-util-1.5.2-6.el7.x86_64 2/6
Installing : httpd-tools-2.4.6-90.el7.centos.x86_64 3/6
Installing : centos-logos-70.0.6-3.el7.centos.noarch 4/6
Installing : mailcap-2.1.41-2.el7.noarch 5/6
Installing : httpd-2.4.6-90.el7.centos.x86_64 6/6
Verifying : mailcap-2.1.41-2.el7.noarch 1/6
Verifying : httpd-tools-2.4.6-90.el7.centos.x86_64 2/6
Verifying : apr-util-1.5.2-6.el7.x86_64 3/6
Verifying : httpd-2.4.6-90.el7.centos.x86_64 4/6
Verifying : apr-1.4.8-5.el7.x86_64 5/6
Verifying : centos-logos-70.0.6-3.el7.centos.noarch 6/6
Installed:
httpd.x86_64 0:2.4.6-90.el7.centos
Dependency Installed:
apr.x86_64 0:1.4.8-5.el7
apr-util.x86_64 0:1.5.2-6.el7
centos-logos.noarch 0:70.0.6-3.el7.centos
httpd-tools.x86_64 0:2.4.6-90.el7.centos
mailcap.noarch 0:2.1.41-2.el7
Complete!
Removing intermediate container 9ef4c5080415
---> 114e1e9151fe
Step 5/6 : RUN mkdir -p /etc/mail
---> Running in 7e0a435fc46d
Removing intermediate container 7e0a435fc46d
---> 6608a26865b5
Step 6/6 : RUN mkdir -p /tmp/siddhesh
---> Running in dc5b6585f487
Removing intermediate container dc5b6585f487
---> 8bc3d4f2d628
Successfully built 8bc3d4f2d628
Successfully tagged apache_centos:DockerFile
[root@siddhesh ~]#Once the build process completes, run following command to see the newly created image using Dockerfile.
[root@siddhesh ~]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
apache_centos DockerFile 8bc3d4f2d628 2 minutes ago 599MB
centos 7 5e35e350aded 4 months ago 203MB
[root@siddhesh ~]#You can verify its author and more details using docker inspect command.
[root@siddhesh ~]# docker inspect
docker inspect 8bc3d4f2d628
[
{
"Id": "sha256:8bc3d4f2d628503320df7b4f42caa3f2225139103643dda218ebbf6b37aee1ec",
"RepoTags": [
"apache_centos:DockerFile"
],
"RepoDigests": [],
"Parent": "sha256:6608a26865b5aa4ed9486d885e0ee4ae101fac879ad394cc8264d2a501365f08",
"Comment": "",
"Created": "2020-04-07T17:41:06.030180259Z",
"Container": "dc5b6585f487cd6f299afd671427c578a26c7fc3ba225131371341b7d0178f32",
"ContainerConfig": {
"Hostname": "",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/bin/sh",
"-c",
"mkdir -p /tmp/siddhesh"
],
"Image": "sha256:6608a26865b5aa4ed9486d885e0ee4ae101fac879ad394cc8264d2a501365f08",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {
"org.label-schema.build-date": "20191001",
"org.label-schema.license": "GPLv2",
"org.label-schema.name": "CentOS Base Image",
"org.label-schema.schema-version": "1.0",
"org.label-schema.vendor": "CentOS"
}
},
"DockerVersion": "19.03.4",
"Author": "Siddhesh Kadam siddhesh@tecgeek.info",
"Config": {
"Hostname": "",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/bin/bash"
],
"ArgsEscaped": true,
"Image": "sha256:6608a26865b5aa4ed9486d885e0ee4ae101fac879ad394cc8264d2a501365f08",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {
"org.label-schema.build-date": "20191001",
"org.label-schema.license": "GPLv2",
"org.label-schema.name": "CentOS Base Image",
"org.label-schema.schema-version": "1.0",
"org.label-schema.vendor": "CentOS"
}
},
"Architecture": "amd64",
"Os": "linux",
"Size": 598771646,
"VirtualSize": 598771646,
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/66d706262f30f87f7cc56a2b4d3ef8a5b4bdf9e768aa3e2c95c88bc95568e30a/diff:/var/lib/docker/overlay2/85b9608cd1ad3c839a492e663c9c7eefa4491f11f148286ced6ab3cb46393914/diff:/var/lib/docker/overlay2/9713e2399502959db40eda79c5a754c9bd2e990331b609ce354c170edf20e159/diff:/var/lib/docker/overlay2/124eb368a97a5dec6e0b01ed7576d040e29076e8d5a58bc7008b43a8ff63ac93/diff",
"MergedDir": "/var/lib/docker/overlay2/7297a1b073fcd04dc8603b1fbd87b70d86be3659d1751d9bce23d92acfe9f988/merged",
"UpperDir": "/var/lib/docker/overlay2/7297a1b073fcd04dc8603b1fbd87b70d86be3659d1751d9bce23d92acfe9f988/diff",
"WorkDir": "/var/lib/docker/overlay2/7297a1b073fcd04dc8603b1fbd87b70d86be3659d1751d9bce23d92acfe9f988/work"
},
"Name": "overlay2"
},
"RootFS": {
"Type": "layers",
"Layers": [
"sha256:77b174a6a187b610e4699546bd973a8d1e77663796e3724318a2a4b24cb07ea0",
"sha256:19b25d87d66b2fedce1264d3022c6e68da83850488ae473e3ac672ed8cdfb3fa",
"sha256:cdf91c18ff3b17f4d3a96537739a8bf195eeb817191d591675449715ffb8c234",
"sha256:bf93daff45ebfb71fab99087949c3aa38bb03367cd35488ac3e8348a75146bf2",
"sha256:2ff5e40a310c29260cc276d09f590fb513145f068b5d6450f03d76c3b1f29728"
]
},
"Metadata": {
"LastTagTime": "2020-04-07T17:41:06.10870629Z"
}
}
]
[root@siddhesh ~]#
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