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Hackernoon logoIntroduction to Buildah: A CLI Tool For Building Images by@sudip-sengupta

Introduction to Buildah: A CLI Tool For Building Images

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@sudip-senguptaSudip Sengupta

Solution Architect | Technical Content Writer

Buildah is a tool for building OCI-compatible images through a lower-level coreutils interface. Similar to Podman, Buildah doesn't depend on a daemon such as Docker or CRI-O, and it doesn't require root privileges. Buildah provides a command-line tool that replicates all the commands found in a Dockerfile. This allows you to issue Buildah commands from a scripting language such as Bash.

This tutorial shows you how to:

  • Use Buildah to package a web-application as a container starting from an existing image, and then run your application with Podman and Docker
  • Use Buildah to package a web-application as a container starting from scratch
  • Use Buildah to package a web-application as a container starting from a Dockerfile
  • Use Buildah to modify an existing container image
  • Push images to a public repository

Prerequisites

In this tutorial, we assume basic familiarity with Docker or Podman. To learn about Podman, see our Podman for Docker Users tutorial.

  • Buildah. Use the 
    buildah --version
     command to verify if Buildah is installed:
buildah --version

The following example output shows that Buildah is installed on your computer:

buildah version 1.11.6 (image-spec 1.0.1-dev, runtime-spec 1.0.1-dev)

If Buildah is not installed, follow the instructions from the Buildah Install page.

  • Podman. Enter the following command to check if Podman is installed on your system:
podman version

The following example output shows that Podman is installed on your computer:

buildah version 1.11.6 (image-spec 1.0.1-dev, runtime-spec 1.0.1-dev)

If Buildah is not installed, follow the instructions from the Buildah Install page.

  • Podman. Enter the following command to check if Podman is installed on your system:
podman version

The following example output shows that Podman is installed on your computer:

Version:            1.6.4
RemoteAPI Version:  1
Go Version:         go1.12.12
OS/Arch:            linux/amd64

Refer the Podman Installation Instructions page for details on how to install Podman.

  • Docker. Use the following command to see if Docker is installed on your system:
docker --version

The following example output shows that Docker is installed on your computer:

Docker version 18.06.3-ce, build d7080c1

For details about installing Docker, refer to the Install Docker page.

Package a Web-based Application as a Container Starting from an Existing Image

In this section, you'll use Buildah to package a web-based application as a container, starting from the Alpine Linux image. Then, you'll run your container image with Podman and Docker.

Alpine Linux is only 5 MB in size, and it lacks several prerequisites that are required to run ExpressJS. Thus, you'll use 

apk
 to install these prerequisites.

1. Enter the following command to create a new container image based on the 

alpine
 image, and store the name of your new image in an environment variable named 
container
:

container=$(buildah from alpine)
Getting image source signatures
Copying blob c9b1b535fdd9 skipped: already exists
Copying config e7d92cdc71 done
Writing manifest to image destination
Storing signatures

☞ Note that, by default, Buildah constructs the name of the container by appending 

-working-container
 to the name:

echo $container
alpine-working-container

You can override the default behavior by specifying the --name flag with the name of the working container. The following example creates a container image called 

example-container
:

example_container=$(buildah from --name "example-container" alpine)
echo $example_container
example-container

2. The Alpine Linux image you just pulled is only 5 MB in size and it lacks the basic utilities such as Bash. Run the following command to verify your new container image:

buildah run $container bash

The following output shows that the container image has been created, but bash is not yet installed:

ERRO[0000] container_linux.go:346: starting container process caused "exec: \"bash\": executable file not found in $PATH"
container_linux.go:346: starting container process caused "exec: \"bash\": executable file not found in $PATH"
error running container: error creating container for [bash]: : exit status 1
ERRO exit status 1

3. To install Bash, enter the 

buildah run
 command and specify:

  • The name of the container (
    $container
    )
  • Two dashes. The commands after 
    --
     are passed directly to the container.
  • The command you want to execute inside the container (
    apk add bash
    )
buildah run $container -- apk add bash
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/community/x86_64/APKINDEX.tar.gz
(1/5) Installing ncurses-terminfo-base (6.1_p20191130-r0)
(2/5) Installing ncurses-terminfo (6.1_p20191130-r0)
(3/5) Installing ncurses-libs (6.1_p20191130-r0)
(4/5) Installing readline (8.0.1-r0)
(5/5) Installing bash (5.0.11-r1)
Executing bash-5.0.11-r1.post-install
Executing busybox-1.31.1-r9.trigger
OK: 15 MiB in 19 packages

4. Similarly to how you've installed 

bash
, run the 
buildah run
 command to install 
node
 and 
npm
:

buildah run $container -- apk add --update nodejs nodejs-npm
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/community/x86_64/APKINDEX.tar.gz
(1/8) Installing ca-certificates (20191127-r1)
(2/8) Installing c-ares (1.15.0-r0)
(3/8) Installing libgcc (9.2.0-r3)
(4/8) Installing nghttp2-libs (1.40.0-r0)
(5/8) Installing libstdc++ (9.2.0-r3)
(6/8) Installing libuv (1.34.0-r0)
(7/8) Installing nodejs (12.15.0-r1)
(8/8) Installing npm (12.15.0-r1)
Executing busybox-1.31.1-r9.trigger
Executing ca-certificates-20191127-r1.trigger
OK: 73 MiB in 27 packages

5. You can use the 

buildah config
 command to set the image configuration values. The following command sets the working directory to
/usr/src/app/
:

buildah config --workingdir /usr/src/app/ $container

6. To initialize a new JavaScript project, run the 

npm init -y
 command inside the container:

buildah run $container -- npm init -y
Wrote to /package.json:

{
  "name": "",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "directories": {
    "lib": "lib"
  },
  "dependencies": {},
  "devDependencies": {},
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}

7. Issue the following command to install Express.JS:

buildah run $container -- npm install express --save
npm WARN @1.0.0 No description
npm WARN @1.0.0 No repository field.

+ express@4.17.1
added 1 package from 8 contributors and audited 126 packages in 1.553s
found 0 vulnerabilities

8. Create a file named 

HelloWorld.js
 and copy in the following JavaScript source code:

const express = require('express')
const app = express()
const port = 3000

app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, () => console.log(`Example app listening on port ${port}!`))

9. To copy the 

HelloWorld.js
 file to your container's working directory, enter the 
buildah copy
 command specifying:

  • The name of the container (
    $container
    )
  • The name of the file you want to copy (
    HelloWorld.js
    )
buildah copy $container HelloWorld.js
c26df5d060c589bda460c34d40c3e8f47f1e401cdf41b379247d23eca24b1c1d

☞ You can copy a file to a different container by passing the name of the destination directory as an argument. The following example command copies the 

HelloWorld.js
 to the 
/temp
 directory:

buildah copy $container HelloWorld.js /temp

10. To set the entry point for your container, enter the 

buildah config
command with the 
--entrypoint
 argument:

buildah config --entrypoint "node HelloWorld.js" $container

11. At this point, you're ready to write the new image using the 

buildah commit
 command. It takes two parameters:

  • The  name of the container image (
    $container
    )
  • The name of the new image (
    buildah-hello-world
    )
buildah commit $container buildah-hello-world
Getting image source signatures
Copying blob 5216338b40a7 skipped: already exists
Copying blob 821cca548ffe done
Copying config 0d9f23545e done
Writing manifest to image destination
Storing signatures
0d9f23545ed69ace9be47ed081c98b4ae182801b7fe5b7ef00a49168d65cf4e5

☞ If the provided image name doesn't begin with a registry name, Buildah defaults to adding 

localhost
 to the name of the image.

12. The following command lists your Buildah images:

buildah images
REPOSITORY                              TAG         IMAGE ID       CREATED          SIZE
localhost/buildah-hello-world           latest      0d9f23545ed6   56 seconds ago   71.3 MB

Running Your Buildah Image with Podman

1. To run your image with Podman, you must first make sure your image is visible in Podman:

podman images

The following example output shows the container image created in the previous steps:

REPOSITORY                              TAG         IMAGE ID       CREATED              SIZE
localhost/buildah-hello-world           latest      0d9f23545ed6   About a minute ago   71.3 MB

2. Run the 

buildah-hello-world
 image by entering the 
podman run
 command with the following arguments:

  • dt
     to specify that the container should be run in the background, and that Podman should allocate a pseudo-TTY for it.
  • -p
     with the port on host (3000) that'll be forwarded to the container port (3000), separated by 
    :
    .
  • The name of your image (
    buildah-hello-world
    )
podman run -dt -p 3000:3000 buildah-hello-world
332d060fc0009a8088349aba672be3601b76553e5df7643d4788c917528cbd8e

3. Use the 

podman ps
 command to see the list of running containers:

podman ps
CONTAINER ID  IMAGE                                 COMMAND  CREATED         STATUS             PORTS                   NAMES
332d060fc000  localhost/buildah-hello-world:latest  /bin/sh  23 seconds ago  Up 21 seconds ago  0.0.0.0:3000->3000/tcp  cool_ritchie

4. To see the running application, point your browser to http://localhost:3000. The application should look as shown in the following screenshot:

5. Now that the functionality of the application has been validated, you can stop the running container:

podman kill 332d060fc000
332d060fc000

Running Your Buildah Image with Docker

The container image you've built in previous sections is compatible with Docker. In this section, we'll walk you through the steps required to run the 

buildah-hello-world
 image with Docker.

1. First, you must push the image to Docker. Enter the 

buildah push
command specifying:

  • The name of the container
  • The destination which uses the following format 
    <TRANSPORT>:<DETAILS>
    .

The following example command uses the 

docker-daemon
 transport to push the 
buildah-hello-world
 image to Docker:

buildah push buildah-hello-world docker-daemon:buildah-hello-world:latest
Getting image source signatures
Copying blob 5216338b40a7 done
Copying blob 821cca548ffe done
Copying config 0d9f23545e done
Writing manifest to image destination
Storing signatures

2. List the Docker images stored on your local machine:

docker images
REPOSITORY            TAG                 IMAGE ID            CREATED             SIZE
buildah-hello-world   latest              0d9f23545ed6        16 minutes ago      64.5MB

3. Run the 

buildah-hello-world
 container image with Docker:

docker run -dt -p 3000:3000 buildah-hello-world
b0f29ff964cd84bf204b3f30f615581c4bb67c4a880aa871ce9c89db48e68720

4. After a few seconds, enter the 

docker ps
 image to display the list of running containers:

docker ps
CONTAINER ID        IMAGE                 COMMAND                  CREATED             STATUS              PORTS                    NAMES
b0f29ff964cd        buildah-hello-world   "/bin/sh -c 'node He…"   16 seconds ago      Up 13 seconds       0.0.0.0:3000->3000/tcp   goofy_chandrasekhar

5. To see the running application, point your browser to http://localhost:3000. The application should look as shown in the following screenshot:

6. Stop the running container with:

docker kill b0f29ff964cd
b0f29ff964cd

Package a Web-application as a Container Starting from Scratch

With Buildah, you can start from an image that's basically an empty shell, except for some container metadata. Once you create such an image, you can then add more packages to it. This is useful when you want to create small containers, with a minimum number of packages installed. In this section, you'll build the 

HelloWorld
 application starting from scratch.

An empty container image doesn't have 

bash
yum
, or any other tools installed. Thus, to install Node and Express.JS on it, you'll mount the container's file-system to a directory on the host, and then use the host's package management system to install the required packages.

1. If you're running Buildah as an unprivileged user, mounting the container's file-system will fail unless you enter the user namespace with the following command:

buildah unshare

2. To start building from an empty container image, enter the 

buildah from
 command, and specify scratch as an argument:

container=$(buildah from scratch)

☞ Note that the above command stores the name of your container image in the container environment variable:

echo $container
working-container-1

3. Issue the following 

buildah mount
 command to mount the container filesystem to a directory on the host, and store the path of the directory in the 
mnt
 environment variable:

mnt=$(buildah mount $container)

4. Use the 

echo
 command to see the name of the directory where the container filesystem is mounted:

echo $mnt
/home/vagrant/.local/share/containers/storage/overlay/e1df4ce46bb88907af45e4edb7379fac8781928ac0cafe0c1a6fc799f4f7a48b/merged

5. You can check that the container filesystem is empty with:

ls $mnt
[root@localhost ~]#

6. Use the hosts' package manager to install software into the container. Enter the 

yum install
 command specifying the following arguments:

  • --installroot
     to configure the alternative install root directory (
    mnt
    ). The packages will be installed relative to this directory.
  • --releasever
     to indicate the version you want to install the packages for. Our example uses 
    centos-release-8
    .
  • The name of the packages you want to install (
    bash
     and 
    coreutils
    ).
  • The 
    -y
     flag to automatically answer 
    yes
     to all questions.
yum install --releasever=centos-release-8 --installroot $mnt bash coreutils  -y
shadow-utils-2:4.6-8.el8.x86_64
systemd-239-18.el8_1.2.x86_64
systemd-libs-239-18.el8_1.2.x86_64
systemd-pam-239-18.el8_1.2.x86_64
systemd-udev-239-18.el8_1.2.x86_64
trousers-lib-0.3.14-4.el8.x86_64
tzdata-2019c-1.el8.noarch
util-linux-2.32.1-17.el8.x86_64
which-2.21-10.el8.x86_64
xz-5.2.4-3.el8.x86_64
xz-libs-5.2.4-3.el8.x86_64
zlib-1.2.11-10.el8.x86_64

Complete!

Note that the above output was truncated for brevity.

7. Clean up the temporary files that 

yum
 created as follows:

yum clean --installroot $mnt all
24 files removed

8. Validate the functionality of your container image. Enter the following

buildah run
 command to run 
bash
 inside of the container:

buildah run $container bash
bash-4.4#

9. You can issue a few commands to make sure everything works as expected. Once you're done, enter the 

exit
 command to terminate the
bash
 session:

exit

10. Enter the following commands to move into the directory where you mounted the container's filesystem, and then download the Node.JS installer:

cd $mnt && wget https://nodejs.org/dist/v12.16.1/node-v12.16.1-linux-x64.tar.xz
--2020-02-24 13:50:07--  https://nodejs.org/dist/v12.16.1/node-v12.16.1-linux-x64.tar.xz
Resolving nodejs.org (nodejs.org)... 104.20.22.46, 104.20.23.46, 2606:4700:10::6814:162e, ...
Connecting to nodejs.org (nodejs.org)|104.20.22.46|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 14591852 (14M) [application/x-xz]
Saving to: 'node-v12.16.1-linux-x64.tar.xz'

node-v12.16.1-linux-x 100%[=======================>]  13.92M  7.25MB/s    in 1.9s

2020-02-24 13:50:09 (7.25 MB/s) - 'node-v12.16.1-linux-x64.tar.xz' saved [14591852/14591852]

11. To extract the files from the archive file and remove the first component from the file names, run the 

tar xf
 command with 
--strip-commponents=1
:

tar xf node-v12.16.1-linux-x64.tar.xz --strip-components=1

12. Delete the archive:

rm -f node-v12.16.1-linux-x64.tar.xz

13. To make sure everything works as expected, use the 

buildah run
command to run 
node
 inside of the container:

buildah run $container node
Welcome to Node.js v12.16.1.
Type ".help" for more information.
>

14. Type 

.exit
 to exit the Node.JS interactive shell.

15. Now that everything is set up, you can install Express.JS and create the
HelloWorld
 project. Follow the steps from 
4
 to 
9
 from the "Build an Express.JS based Image from an Existing Image" section.

16. Once you've finished the above steps, unmount the container filesystem:

buildah unmount $container

17. Execute the 

buildah commit
 command to create a new image called
buildah-demo-from-scratch
:

buildah commit $container buildah-demo-from-scratch
Getting image source signatures
Copying blob a9a2ac73e013 done
Copying config ec14304d59 done
Writing manifest to image destination
Storing signatures
ec14304d5906c7b8fb9a485ff959e4a6c337115245a827858bf6ba808f5f4e0e

18. To see the list of your Buildah images, run the 

buildah images
command:

buildah images
REPOSITORY                            TAG      IMAGE ID       CREATED          SIZE
localhost/buildah-demo-from-scratch   latest   ec14304d5906   3 minutes ago    582 MB

19. You can use the 

buildah inspect
 command to retrieve more details about the 
buildah-demo-from-scratch
 container image:

buildah inspect $container
{
    "Type": "buildah 0.0.1",
    "FromImage": "",
    "FromImageID": "",
    "FromImageDigest": "",
    "Config": "",
    "Manifest": "",
    "Container": "working-container",
    "ContainerID": "f974b8b06921a57edddb5735ee7fc0c7176051ff1b76d0523bf2879d7865afba",
    "MountPoint": "",
    "ProcessLabel": "system_u:system_r:container_t:s0:c435,c738",
    "MountLabel": "system_u:object_r:container_file_t:s0:c435,c738",
    "ImageAnnotations": null,
    "ImageCreatedBy": "",
    "OCIv1": {
        "created": "2020-02-27T14:46:38.379626079Z",
        "architecture": "amd64",
        "os": "linux",
        "config": {
            "Entrypoint": [
                "/bin/sh",
                "-c",
                "node HelloWorld.js"
            ],
            "WorkingDir": "/usr/src/app/"
        },
        "rootfs": {
            "type": "",
            "diff_ids": null
        }
    },
    "Docker": {
        "created": "2020-02-27T14:46:38.379626079Z",
        "container_config": {
            "Hostname": "",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": null,
            "Cmd": null,
            "Image": "",
            "Volumes": null,
            "WorkingDir": "/usr/src/app/",
            "Entrypoint": [
                "/bin/sh",
                "-c",
                "node HelloWorld.js"
            ],
            "OnBuild": [],
            "Labels": null
        },
        "config": {
            "Hostname": "",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": null,
            "Cmd": null,
            "Image": "",
            "Volumes": null,
            "WorkingDir": "/usr/src/app/",
            "Entrypoint": [
                "/bin/sh",
                "-c",
                "node HelloWorld.js"
            ],
            "OnBuild": [],
            "Labels": null
        },
        "architecture": "amd64",
        "os": "linux"
    },
    "DefaultMountsFilePath": "",
    "Isolation": "IsolationOCIRootless",
    "NamespaceOptions": [
        {
            "Name": "cgroup",
            "Host": true,
            "Path": ""
        },
        {
            "Name": "ipc",
            "Host": false,
            "Path": ""
        },
        {
            "Name": "mount",
            "Host": false,
            "Path": ""
        },
        {
            "Name": "network",
            "Host": true,
            "Path": ""
        },
        {
            "Name": "pid",
            "Host": false,
            "Path": ""
        },
        {
            "Name": "user",
            "Host": true,
            "Path": ""
        },
        {
            "Name": "uts",
            "Host": false,
            "Path": ""
        }
    ],
    "ConfigureNetwork": "NetworkDefault",
    "CNIPluginPath": "/usr/libexec/cni:/opt/cni/bin",
    "CNIConfigDir": "/etc/cni/net.d",
    "IDMappingOptions": {
        "HostUIDMapping": true,
        "HostGIDMapping": true,
        "UIDMap": [],
        "GIDMap": []
    },
    "DefaultCapabilities": [
        "CAP_AUDIT_WRITE",
        "CAP_CHOWN",
        "CAP_DAC_OVERRIDE",
        "CAP_FOWNER",
        "CAP_FSETID",
        "CAP_KILL",
        "CAP_MKNOD",
        "CAP_NET_BIND_SERVICE",
        "CAP_SETFCAP",
        "CAP_SETGID",
        "CAP_SETPCAP",
        "CAP_SETUID",
        "CAP_SYS_CHROOT"
    ],
    "AddCapabilities": [],
    "DropCapabilities": [],
    "History": [
        {
            "created": "2020-02-27T14:56:04.319174231Z"
        }
    ],
    "Devices": []
}

20. The steps for running the image are similar to the ones from the "Running your Buildah Image with Podman". For the sake of brevity, those steps are not repeated here.

Package a Web-application as a Container Starting from a Dockerfile

1. Create a directory called 

from-dockerfile
 and then move into it:

mkdir from-dockerfile && cd from-dockerfile/

2. Use a plain-text editor to create a file called

Dockerfile
, and copy in the following snippet:

FROM node:10
WORKDIR /usr/src/app
RUN npm init -y
RUN npm install express --save
COPY HelloWorld.js .
CMD [ "node", "HelloWorld.js" ]

3. Create a file named 

HelloWorld.js
 with the following content:

const express = require('express')
const app = express()
const port = 3000

app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, () => console.log(`Example app listening on port ${port}!`))

4. Build the container image. Enter the buildah bud command specifying the -t flag with the name Buildah should apply to the built image, and the build context directory (

.
):

buildah bud -t buildah-from-dockerfile .
STEP 1: FROM node:10
STEP 2: WORKDIR /usr/src/app
STEP 3: RUN npm init -y
Wrote to /usr/src/app/package.json:

{
  "name": "app",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}


STEP 4: RUN npm install express --save
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN app@1.0.0 No description
npm WARN app@1.0.0 No repository field.

+ express@4.17.1
added 50 packages from 37 contributors and audited 126 packages in 4.989s
found 0 vulnerabilities

STEP 5: COPY HelloWorld.js .
STEP 6: CMD [ "node", "HelloWorld.js" ]
STEP 7: COMMIT buildah-from-dockerfile
Getting image source signatures
Copying blob 7948c3e5790c skipped: already exists
Copying blob 4d1ab3827f6b skipped: already exists
Copying blob 69dfa7bd7a92 skipped: already exists
Copying blob 01727b1a72df skipped: already exists
Copying blob 1d7382716a27 skipped: already exists
Copying blob 03dc1830d2d5 skipped: already exists
Copying blob 1e1795dd2c10 skipped: already exists
Copying blob c8a8d3d42bc1 skipped: already exists
Copying blob 072dcfd76a1e skipped: already exists
Copying blob fc67e152fd86 done
Copying config 7619bf0e33 done
Writing manifest to image destination
Storing signatures
7619bf0e33165f5c3dc6da00cb101f2195484bff3e59f4c6f57a41c07647d407
7619bf0e33165f5c3dc6da00cb101f2195484bff3e59f4c6f57a41c07647d407

5. The following command lists your Buildah images:

buildah images
REPOSITORY                          TAG      IMAGE ID       CREATED             SIZE
localhost/buildah-from-dockerfile   latest   7619bf0e3316   52 seconds ago      944 MB

6. Enter the 

podman run
 command to run un the 
buildah-from-dockerfile
image:

podman run -dt -p 3000:3000 buildah-from-dockerfile
dbbae173dca0ca5b602c0b9a70055886381cb7df5ae25fbb4bd81c75a4bcb50d
[vagrant@localhost buildah-hello-world]$ podman ps
CONTAINER ID  IMAGE                                     COMMAND               CREATED        STATUS            PORTS                   NAMES
dbbae173dca0  localhost/buildah-from-dockerfile:latest  node HelloWorld.j...  4 seconds ago  Up 3 seconds ago  0.0.0.0:3000->3000/tcp  priceless_cartwright

7. Point your browser to http://localhost:3000, and you should see something similar to the following screenshot:

8. Stop the container by entering the 

podman kill
 command followed by the identifier of the 
buildah-from-dockerfile
 container (
dbbae173dca0
):

podman kill dbbae173dca0
dbbae173dca0ca5b602c0b9a70055886381cb7df5ae25fbb4bd81c75a4bcb50d

Use Buildah to Modify a Container Image

With Buidah, you can modify a container in the following ways:

  • Mount the container and copy files to it
  • Using the buildah config command
  • Using the buildah copy command

Mount the Container and Copy Files to It

1. Run the following command to create a new container using the

buildah-from-dockerfile
 image as a starting point:

buildah from buildah-from-dockerfile

The above command prints the name of your new container:

buildah-from-dockerfile-working-container

2. Use the 

buildah list
 command to see the list of your working containers:

buildah containers
CONTAINER ID  BUILDER  IMAGE ID     IMAGE NAME                       CONTAINER NAME
78c4225c8c37     *     7619bf0e3316 localhost/buildah-from-docker... buildah-from-dockerfile-working-container

3. If you're running Buildah as an unprivileged user, enter the user namespace with:

buildah unshare

4. Mount the container filesystem to a directory on the host, and save the name of that directory in an environment variable called 

mount
 by entering the following command:

mount=$(buildah mount buildah-from-dockerfile-working-container)

5. You can use the 

echo
 command to print the path of the folder where the container filesystem is mounted:

echo $mount
/home/vagrant/.local/share/containers/storage/overlay/83b2d731b920653a569795cf75f4902a1e148dab61f4cb41bcc37bae0f5d6655/merged

6. Move into the 

/usr/src/app
 folder:

cd $mount/usr/src/app/

7. Open the 

HelloWorld.js
 file in a plain-text editor, and edit the line that prints the 
Hello World!
 message to:

app.get('/', (req, res) => res.send('Hello World (modified with Buildah)!'))

Your 

HelloWorld.js
 file should look similar to the listing below:

cat HelloWorld.js
const express = require('express')
const app = express()
const port = 3000

app.get('/', (req, res) => res.send('Hello World (modified with Buildah)!'))

app.listen(port, () => console.log(`Example app listening on port ${port}!`))

8. Save the changes to a new container image called 

modified-container
:

buildah commit buildah-from-dockerfile-working-container modified-container
Getting image source signatures
Copying blob 7948c3e5790c skipped: already exists
Copying blob 4d1ab3827f6b skipped: already exists
Copying blob 69dfa7bd7a92 skipped: already exists
Copying blob 01727b1a72df skipped: already exists
Copying blob 1d7382716a27 skipped: already exists
Copying blob 03dc1830d2d5 skipped: already exists
Copying blob 1e1795dd2c10 skipped: already exists
Copying blob c8a8d3d42bc1 skipped: already exists
Copying blob 072dcfd76a1e skipped: already exists
Copying blob fc67e152fd86 skipped: already exists
Copying blob a546faf200ff done
Copying config d3ac43ac8d done
Writing manifest to image destination
Storing signatures
d3ac43ac8da20aef987367353e56e22a1a2330176c08e255c72670b3b08c1e14

9. If you run the 

buildah images
 command, you should see both images:

buildah images
REPOSITORY                          TAG      IMAGE ID       CREATED             SIZE
localhost/modified-container        latest   d3ac43ac8da2   46 seconds ago      944 MB
localhost/buildah-from-dockerfile   latest   7619bf0e3316   14 minutes ago      944 MB

10. Unmount the root filesystem of your container by entering the following 

buildah unmount
 command:

buildah unmount buildah-from-dockerfile-working-container
78c4225c8c377d8a018583586e2f76932204f20b4f3621fedb1ab3d41f8a3240

11. Run the 

modified-container
 image with Podman:

podman run -dt -p 3000:3000 modified-container
70105ac094b672c98f56290d25fa5406a7c51bf401cff586c7a356b4f19f1320

12. Enter the 

podman ps 
command to print the list of running containers:

podman ps
CONTAINER ID  IMAGE                                COMMAND               CREATED        STATUS            PORTS                   NAMES
70105ac094b6  localhost/modified-container:latest  node HelloWorld.j...  4 seconds ago  Up 4 seconds ago  0.0.0.0:3000->3000/tcp  pedantic_rhodes

13. To see the modified application in action, point your browser to http://localhost:3000:

Modify a Container with the 
buildah config
 Command

1. To see the list of your local container images, use the 

buildah images
command:

buildah containers
CONTAINER ID  BUILDER  IMAGE ID     IMAGE NAME                       CONTAINER NAME
305591a5116c     *     7619bf0e3316 localhost/buildah-from-docker... buildah-from-dockerfile-working-container

2. In this example, you'll modify the configuration value for the

author
field. Run the 
buildah config
 command specifying the following parameters:

  • --author
     with the name of the author.
  • The identifier of the container (
    305591a5116c
    )
buildah config --author='Andrei Popescu' 305591a5116c

3. Enter the 

buildah inspect
 command to display detailed information about your container:

buildah inspect 305591a5116c
{
        "Docker": {
        "created": "2020-02-24T14:41:01.41295511Z",
        "container_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",
                "NODE_VERSION=10.19.0",
                "YARN_VERSION=1.21.1"
            ],
            "Cmd": [
                "node",
                "HelloWorld.js"
            ],
            "Image": "",
            "Volumes": null,
            "WorkingDir": "/usr/src/app",
            "Entrypoint": [
                "docker-entrypoint.sh"
            ],
            "OnBuild": [],
            "Labels": null
        },
        "author": "Andrei Popescu",
        "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",
                "NODE_VERSION=10.19.0",
                "YARN_VERSION=1.21.1"
            ],
            "Cmd": [
                "node",
                "HelloWorld.js"
            ],
            "Image": "",
            "Volumes": null,
            "WorkingDir": "/usr/src/app",
            "Entrypoint": [
                "docker-entrypoint.sh"
            ],
            "OnBuild": [],
            "Labels": null
        },

Note that that the above output was truncated for brevity.

As you can see, the 

author
 field has been updated:

"author": "Andrei Popescu",

Modifying a Container with the 
buildah copy
 Command

1. List your Buildah images with:

buildah images
REPOSITORY                          TAG      IMAGE ID       CREATED          SIZE
localhost/buildah-from-dockerfile   latest   4c4c1019785e   19 seconds ago   944 MB
docker.io/library/node              10       aa6432763c11   5 days ago       940 MB

2. Create a new working container using 

buildah-from-dockerfile
 as the starting image:

container=$(buildah from buildah-from-dockerfile)

3. The above command saves the name of your new working container into an environment variable called 

container
. Use the 
echo
 command to see the name of your new container:

echo $container
buildah-from-dockerfile-working-container

4. Use a plain-text editor to open the 

HelloWorld.js
. Next, modify the line of code that prints the 
Hello World!
 message to the following:

app.get('/', (req, res) => res.send('Hello World (modified with the buildah copy command)!'))

Your 

HelloWorld.js
 file should look similar to the following listing:

const express = require('express')
const app = express()
const port = 3000

app.get('/', (req, res) => res.send('Hello World (modified with the buildah copy command)!'))

app.listen(port, () => console.log(`Example app listening on port ${port}!`))

5. Enter the following 

buildah copy
 command to copy the content of the
HelloWorld.js
 file into the container's 
/usr/src/app/
 directory:

buildah copy buildah-from-dockerfile-working-container HelloWorld.js /usr/src/app/
bf36dd7b6ba5d3f520835f5e850e4303bd830bd0934d1cb8a11c4c45cf3ebcb8

6. The 

buildah run
 is different from the 
podman run
 command. Since Buildah is a tool aimed at building images, you can't use 
buildah run
 to map ports or mount volumes. You can think of it as similar to the 
RUN
command from a Dockerfile. Thus, to test the changes before saving them to a new image, you must run a shell inside of the container:

buildah run $container -- bash

7. Use the 

cat
 command to list the contents of the 
HelloWorld.js
 file:

cat HelloWorld.js
const express = require('express')
const app = express()
const port = 3000

app.get('/', (req, res) => res.send('Hello World (modified with the buildah copy command)!'))

app.listen(port, () => console.log(`Example app listening on port ${port}!`))

8. Type 

exit
 to return to the host:

exit

9. Save your changes to a new container image named 

modified-with-copy
. Enter the 
buildah commit
 command passing it the following parameters:

  • The name of your working container (
    $container
    )
  • The name of your new container (
    modified-with-copy
    )
buildah commit $container modified-with-copy
Getting image source signatures
Copying blob 2c995a2087c1 skipped: already exists
Copying blob 00adafc8e77b skipped: already exists
Copying blob d040e6423b7a skipped: already exists
Copying blob 162804eaaa1e skipped: already exists
Copying blob 91daf9fc6311 skipped: already exists
Copying blob 236d3097407d skipped: already exists
Copying blob 92086f81cd8d skipped: already exists
Copying blob 90aa9e20811b skipped: already exists
Copying blob cea8dd7dcda1 skipped: already exists
Copying blob 490adad7924f skipped: already exists
Copying blob fc29e33720c1 done
Copying config c6df996bc7 done
Writing manifest to image destination
Storing signatures
c6df996bc740c9670c87470f65124f8a8a3b74ecde3dc38038530a98209e5148

10. Enter the 

podman images
 command to list the images available on your system:

podman images
podman images
REPOSITORY                          TAG      IMAGE ID       CREATED              SIZE
localhost/modified-with-copy        latest   c6df996bc740   About a minute ago   944 MB
localhost/buildah-from-dockerfile   latest   efd9caedf198   24 minutes ago       944 MB
docker.io/library/node              10       aa6432763c11   5 days ago           940 MB

11. Run the modified image with Podman:

podman run -dt -p 3000:3000 modified-with-copy
f2bf06e4d6010adab6acf92db063a4c11f821fb96c2912266ac9900752f53bc4

12. Make sure that the modified container works as expected by pointing your browser to http://localhost:3000:

Use Buildah to Push an Image to a Public Repository

In this section, we'll show how you can push a Buildah image to Quay.io. Then, you'll use Docker to pull and run it on your system.

1. Login to Quay.io with the following command:

buildah login quay.io

Buildah will prompt you to enter your username and password:

Username:
Password:
Login Succeeded!

2. Use the 

buildah images
 command to see the list of Buildah images available on your system:

buildah images
REPOSITORY                          TAG      IMAGE ID       CREATED          SIZE
localhost/modified-with-copy        latest   c6df996bc740   31 minutes ago   944 MB
localhost/buildah-from-dockerfile   latest   efd9caedf198   54 minutes ago   944 MB
docker.io/library/node              10       aa6432763c11   5 days ago       940 MB

3. To push an image to Quay.io, enter the 

buildah push
 command specifying:

  • The source.
  • The destination. This uses the following format 
    <transport>:<destination>
    .

The following example command pushes the 

modified-with-copy
 to the
andreipope/modified-with-copy 
repository:

buildah push modified-with-copy docker://quay.io/andreipope/modified-with-copy:latest
Getting image source signatures
Copying blob d040e6423b7a done
Copying blob 236d3097407d done
Copying blob 2c995a2087c1 done
Copying blob 00adafc8e77b skipped: already exists
Copying blob 91daf9fc6311 done
Copying blob 162804eaaa1e done
Copying blob 92086f81cd8d skipped: already exists
Copying blob 90aa9e20811b skipped: already exists
Copying blob cea8dd7dcda1 skipped: already exists
Copying blob 490adad7924f skipped: already exists
Copying blob fc29e33720c1 skipped: already exists
Copying config c6df996bc7 done
Writing manifest to image destination
Copying config c6df996bc7 done
Writing manifest to image destination
Writing manifest to image destination
Storing signatures

4. Pull the image from Quay.io using the 

docker pull
 command:

docker pull quay.io/andreipope/modified-with-copy:latest
latest: Pulling from andreipope/modified-with-copy
571444490ac9: Pull complete
a8c44c6007c2: Pull complete
78082700aa2c: Pull complete
c3a1a87b600e: Pull complete
307b97780b43: Pull complete
e6bc907e1abd: Pull complete
f7d60f9c5e35: Pull complete
6d95f9b81e1b: Pull complete
3fc72998ebc8: Pull complete
632905c48be3: Pull complete
29b4e1262307: Pull complete
Digest: sha256:a57849f1f639b5f4e01af33fdf4b86238dead6ddaf8f95b4e658863dfcf22700
Status: Downloaded newer image for quay.io/andreipope/modified-with-copy:latest

5. List your Docker images:

docker images
REPOSITORY                              TAG                 IMAGE ID            CREATED             SIZE
quay.io/andreipope/modified-with-copy   latest              05b3081ac594        About an hour ago   914MB

6. Issue the following 

docker run
 command to run the 
modified-with-copy
 image:

docker run -dt -p 3000:3000 quay.io/andreipope/modified-with-copy
6394d8a8b60106125a062504d3764fcd0034b06947cfe303f9be0e87b82fee88

7. Point your browser to http://localhost:3000 and you should see something similar to the screenshot below:

In this tutorial, you learned how to:

  • Use Buildah to build an image from an existing image
  • Build an image from Scratch
  • Build an image from a Dockerfile
  • Use Buildah to modify an existing container
  • Run your Buildah images with Podman and Docker
  • Push images to a public repository

We hope this blog post has been helpful and that now you know how to build container images with Buildah.

Thanks for reading!

About the author - Sudip is a Solution Architect with more than 15 years of working experience, and is the founder of Javelynn. He likes sharing his knowledge by regularly writing for HackernoonDZoneAppfleet and many more. And while he is not doing that, he must be fishing or playing chess.

Previously posted at https://appfleet.com/.

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