Click on each book below to review & buy on Amazon.
As an Amazon Associate, I earn from qualifying purchases.
RHCSA - Manage Containers: Build a Container From a Containerfile
A Containerfile, often referred to as a Dockerfile in the context of Docker containers, is a plain text configuration file used to define the specifications and instructions for building a containerized application environment. It serves as a blueprint for creating container images by specifying the base image, desired software dependencies, configuration settings, and executable commands.
Containerfile
Although creating your own Containerfile is not an exam objective, we will be creating one here so that you can practice the exam objective of building a container from a Containerfile.
Below is a basic Containerfile for building a container image using the Red Hat Universal Base Image (UBI) as the base layer, and installing the nginx web server on top of this:
# Use the Red Hat Universal Base Image (UBI) as the base image.
FROM registry.access.redhat.com/ubi8/ubi
# Label the image with your name or any other relevant information.
LABEL maintainer="DTV Linux Student"
# Update the package repository and install Nginx.
RUN yum update -y && yum install -y nginx && yum clean all
# Expose port 80 to allow incoming HTTP traffic.
EXPOSE 80
# Start Nginx as the main process when a container based on this image is run.
CMD ["nginx", "-g", "daemon off;"]
The following provides some information on what each line in the Containerfile does:
FROM registry.access.redhat.com/ubi8/ubi: Specifies the base image to use, in this case, Red Hat UBI version 8.LABEL maintainer="DTV Linux Student": Optional metadata to label the image with the maintainer's information.RUN yum update -y && yum install -y nginx && yum clean all: This line updates the package repository, installs Nginx using theyumpackage manager, and then cleans up the package cache to reduce the image size.EXPOSE 80: The container will listen on port 80, allowing you to map it to the host system when you run a container.CMD ["nginx", "-g", "daemon off;"]: Specifies the command to run when a container is started. In this case, it starts the Nginx web server and keeps it running in the foreground.
Building a Container
To create a container start by ensuring you have a Containerfile. If you haven't already, generate a file named Containerfile in your current directory and populate it with the example content provided above.
The below exercise will get you building a container image:
Build an image called my-container using the Containerfile and tag it with version 1.0.0:
The final . in the command below ensures the current directory is used when looking for the Containerfile.
podman build -t my-container:1.0.0 .
You will see the build process occur on screen, with each STEP corresponding to an entry in the Containerfile:
STEP 1/5: FROM registry.access.redhat.com/ubi8/ubi
STEP 2/5: LABEL maintainer="Your Name <your@email.com>"
--> 271b88e8d1d
STEP 3/5: RUN yum update -y && yum install -y nginx && yum clean all
Updating Subscription Management repositories.
Unable to read consumer identity
Subscription Manager is operating in container mode.
Red Hat Enterprise Linux 8 for x86_64 - BaseOS 18 MB/s | 63 MB 00:03
Red Hat Enterprise Linux 8 for x86_64 - AppStre 12 MB/s | 59 MB 00:05
Red Hat Universal Base Image 8 (RPMs) - BaseOS 1.5 MB/s | 716 kB 00:00
Red Hat Universal Base Image 8 (RPMs) - AppStre 5.5 MB/s | 2.9 MB 00:00
Red Hat Universal Base Image 8 (RPMs) - CodeRea 257 kB/s | 99 kB 00:00
Dependencies resolved.
Nothing to do.
Complete!
Updating Subscription Management repositories.
Unable to read consumer identity
Subscription Manager is operating in container mode.
Last metadata expiration check: 0:00:11 ago on Sat Sep 2 11:10:31 2023.
Dependencies resolved.
======================================================================================================================
Package Arch Version Repository Size
======================================================================================================================
Installing:
nginx x86_64 1:1.14.1-9.module+el8.0.0+4108+af250afe rhel-8-for-x86_64-appstream-rpms 570 k
Installing dependencies:
dejavu-fonts-common noarch 2.35-7.el8 rhel-8-for-x86_64-baseos-rpms 74 k
dejavu-sans-fonts noarch 2.35-7.el8 rhel-8-for-x86_64-baseos-rpms 1.5 M
fontconfig x86_64 2.13.1-4.el8 rhel-8-for-x86_64-baseos-rpms 274 k
...
perl-podlators noarch 4.11-1.el8 rhel-8-for-x86_64-baseos-rpms 118 k
perl-threads x86_64 1:2.21-2.el8 rhel-8-for-x86_64-baseos-rpms 61 k
perl-threads-shared x86_64 1.58-2.el8 rhel-8-for-x86_64-baseos-rpms 48 k
Installing weak dependencies:
perl-IO-Socket-IP noarch 0.39-5.el8 rhel-8-for-x86_64-appstream-rpms 47 k
perl-IO-Socket-SSL noarch 2.066-4.module+el8.3.0+6446+594cad75 rhel-8-for-x86_64-appstream-rpms 298 k
perl-Mozilla-CA noarch 20160104-7.module+el8.3.0+6498+9eecfe51 rhel-8-for-x86_64-appstream-rpms 15 k
Enabling module streams:
nginx 1.14
perl 5.26
perl-IO-Socket-SSL 2.066
perl-libwww-perl 6.34
Transaction Summary
======================================================================================================================
Install 69 Packages
Total download size: 20 M
Installed size: 57 M
Downloading Packages:
(1/69): perl-Data-Dumper-2.167-399.el8.x86_64.r 155 kB/s | 58 kB 00:00
(2/69): perl-Scalar-List-Utils-1.49-2.el8.x86_6 172 kB/s | 68 kB 00:00
(3/69): perl-PathTools-3.74-1.el8.x86_64.rpm 222 kB/s | 90 kB 00:00
...
(67/69): libwebp-1.0.0-8.el8_7.x86_64.rpm 1.5 MB/s | 273 kB 00:00
(68/69): libXpm-3.5.12-9.el8_7.x86_64.rpm 215 kB/s | 58 kB 00:00
(69/69): libtiff-4.0.9-28.el8_8.x86_64.rpm 1.1 MB/s | 189 kB 00:00
--------------------------------------------------------------------------------
Total 4.2 MB/s | 20 MB 00:04
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Preparing : 1/1
Installing : libjpeg-turbo-1.5.3-12.el8.x86_64 1/69
Installing : openssl-1:1.1.1k-9.el8_7.x86_64 2/69
Installing : fontpackages-filesystem-1.44-22.el8.noarch 3/69
...
Verifying : libXpm-3.5.12-9.el8_7.x86_64 67/69
Verifying : libwebp-1.0.0-8.el8_7.x86_64 68/69
Verifying : libtiff-4.0.9-28.el8_8.x86_64 69/69
Installed products updated.
Installed:
dejavu-fonts-common-2.35-7.el8.noarch
dejavu-sans-fonts-2.35-7.el8.noarch
fontconfig-2.13.1-4.el8.x86_64
...
perl-podlators-4.11-1.el8.noarch
perl-threads-1:2.21-2.el8.x86_64
perl-threads-shared-1.58-2.el8.x86_64
Complete!
Updating Subscription Management repositories.
Unable to read consumer identity
Subscription Manager is operating in container mode.
42 files removed
--> cf38f1d5e71
STEP 4/5: EXPOSE 80
--> ddd71af09a3
STEP 5/5: CMD ["nginx", "-g", "daemon off;"]
COMMIT my-container:1.0.0
--> 89874198298
Successfully tagged localhost/my-container:1.0.0
898741982987067c403a93369c35681a28bf9546a94390b9560a99c57db5ecff
Verify the container image was create successfully:
podman image list my-container
The command output should resemble:
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/my-container 1.0.0 27a3d9930475 About an hour ago 302 MB
Support DTV Linux
Click on each book below to review & buy on Amazon. As an Amazon Associate, I earn from qualifying purchases.
NordVPN ®: Elevate your online privacy and security. Grab our Special Offer to safeguard your data on public Wi-Fi and secure your devices. I may earn a commission on purchases made through this link.