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Howto for rootless image building from OpenShift

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Signed-off-by: Jesper Skov <jskov@jyskebank.dk>
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Jesper Skov
2020-07-09 07:37:29 +02:00
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![buildah logo](https://cdn.rawgit.com/containers/buildah/master/logos/buildah-logo_large.png)
# Buildah Tutorial 5
## Using Buildah to build images in a rootless OpenShift container
This tutorial will walk you through setting up a container in OpenShift for building images.
The instructions have been tested on OpenShift 4.3.28 with Buildah 1.14.8.
Note that the VFS volume mounting is used instead of the more performant fuse. But the the latter does not work at the moment.
### Prepare a new namespace
Create a new project in OpenShift called `image-build`.
Make the registry URL available to the following steps.
*Note that you need to change this so it matches your OpenShift installation.*
````console
$ export REGISTRY_URL=default-route-openshift-image-registry.apps.whatever.com
````
Login to OpenShift and its registry:
````console
$ oc login -n image-build
Username: ...
Password: ...
Login successful.
You have access to N projects, the list has been suppressed. You can list all projects with 'oc projects'
Using project "image-build".
$ oc whoami -t | podman login -u $(id -u -n) --password-stdin $REGISTRY_URL
Login Succeeded!
````
### Make builder image
This is the image that will host the building. It uses the Buildah stable official image, which is based on Fedora 32.
The image starts a python web server. This allows us to interact with the container via the OpenShift console terminal, demonstrating that building an image works.
First create an ImageStream to hold the image:
````console
$ oc create -f - <<EOF
apiVersion: image.openshift.io/v1
kind: ImageStream
metadata:
name: buildah
EOF
imagestream.image.openshift.io/buildah created
````
Then create the image.
Note that no packages are updated - this should ensure that this tutorial is actually working.
If you are making anything for use in the real world, make sure to update it frequently for security fixes!
````console
$ cat > Containerfile-buildah <<EOF
FROM quay.io/buildah/stable:v1.14.8
RUN touch /etc/subgid /etc/subuid \
&& chmod g=u /etc/subgid /etc/subuid /etc/passwd \
&& echo build:10000:65536 > /etc/subuid \
&& echo build:10000:65536 > /etc/subgid
# Use chroot since the default runc does not work when running rootless
RUN echo "export BUILDAH_ISOLATION=chroot" >> /home/build/.bashrc
# Use VFS since fuse does not work
RUN mkdir -p /home/build/.config/containers \
&& echo "driver=\"vfs\"" > /home/build/.config/containers/storage.conf
USER build
WORKDIR /home/build
# Just keep the container running, allowing "oc rsh" access
CMD ["python3", "-m", "http.server"]
EOF
$ podman build -t $REGISTRY_URL/image-build/buildah -f Containerfile-buildah
STEP 1: FROM quay.io/buildah/stable:v1.14.8
STEP 2: RUN touch /etc/subgid /etc/subuid && chmod g=u /etc/subgid /etc/subuid /etc/passwd && echo build:10000:65536 > /etc/subuid && echo build:10000:65536 > /etc/subgid
--> a25dbbd3824
STEP 3: CMD ["python3", "-m", "http.server"]
STEP 4: COMMIT default-route-openshift-image-registry.../image-build/buildah
--> 9656f2677e3
9656f2677e3e760e071c93ca7cba116871f5549b28ad8595e9134679db2345fc
$ podman push $REGISTRY_URL/image-build/buildah
Getting image source signatures
...
Storing signatures
````
### Create Service Account for building images
Create a service account which is solely used for image building.
````console
$ oc create -f - <<EOF
apiVersion: v1
kind: ServiceAccount
metadata:
name: buildah-sa
EOF
serviceaccount/buildah-sa created
````
You need to assign it the ability to run as the standard `anyuid` [SCC](https://docs.openshift.com/container-platform/4.3/authentication/managing-security-context-constraints.html).
````console
$ oc adm policy add-scc-to-user anyuid -z buildah-sa
clusterrole.rbac.authorization.k8s.io/system:openshift:scc:anyuid added: "buildah-sa"
````
This will give the container *cap_kill*, *cap_setgid*, and *cap_setuid* capabilities which are extras compared to the `restricted` SCC.
Note that *cap_kill* is dropped by the DeploymentConfig, but the two others are required to execute commands with different user ids as an image is built.
With this in place, when you get the Pod running (in a little while!), its YAML state will contain:
````
kind: Pod
metadata:
...
openshift.io/scc: anyuid
...
````
Which tells you that the Pod has been launched with the correct permissions.
#### Create DeploymentConfig
This is a simple DC just to get the container running.
Note that it drops CAP_KILL which is not required.
````console
$ oc create -f - <<EOF
apiVersion: apps.openshift.io/v1
kind: DeploymentConfig
metadata:
name: buildah
spec:
selector:
app: image-builder
replicas: 1
template:
metadata:
labels:
app: image-builder
spec:
serviceAccount: buildah-sa
containers:
- name: buildah
image: image-registry.openshift-image-registry.svc:5000/image-build/buildah
securityContext:
capabilities:
drop:
- KILL
EOF
deploymentconfig.apps.openshift.io/buildah created
````
#### The Buildah container
In the OpenShift console you can now open the Pod's Terminal and try building an image.
This is what the user/platform should look like:
````console
sh-5.0$ id
uid=1000(build) gid=1000(build) groups=1000(build)
sh-5.0$ uname -a
Linux buildah-1-8t74l 4.18.0-147.13.2.el8_1.x86_64 #1 SMP Wed May 13 15:19:35 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
sh-5.0$ capsh --print
Current: = cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot+i
Bounding set =cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot
Ambient set =
Securebits: 00/0x0/1'b0
secure-noroot: no (unlocked)
secure-no-suid-fixup: no (unlocked)
secure-keep-caps: no (unlocked)
secure-no-ambient-raise: no (unlocked)
uid=1000(build)
gid=1000(build)
groups=
````
This is what the Buildah data should look like:
````console
sh-5.0$ buildah version
Version: 1.14.8
Go Version: go1.14
Image Spec: 1.0.1-dev
Runtime Spec: 1.0.1-dev
CNI Spec: 0.4.0
libcni Version:
image Version: 5.4.3
Git Commit:
Built: Thu Jan 1 00:00:00 1970
OS/Arch: linux/amd64
sh-5.0$ buildah info
{
"host": {
"CgroupVersion": "v1",
"Distribution": {
"distribution": "fedora",
"version": "32"
},
"MemTotal": 33726861312,
"MenFree": 20319305728,
"OCIRuntime": "runc",
"SwapFree": 0,
"SwapTotal": 0,
"arch": "amd64",
"cpus": 4,
"hostname": "buildah-1-6hvsw",
"kernel": "4.18.0-147.13.2.el8_1.x86_64",
"os": "linux",
"rootless": true,
"uptime": "61h 10m 39.3s (Approximately 2.54 days)"
},
"store": {
"ContainerStore": {
"number": 0
},
"GraphDriverName": "vfs",
"GraphOptions": null,
"GraphRoot": "/home/build/.local/share/containers/storage",
"GraphStatus": {},
"ImageStore": {
"number": 0
},
"RunRoot": "/var/tmp/1000/containers"
}
}
````
#### Building an image
Now create some files for testing.
This container test file excersises at least some of the critical parts of building an image (package update/installation, execution of commands, and use of volumes).
````console
sh-5.0$ cat > test-script.sh <<EOF
#/bin/bash
echo "Args \$*"
ls -l /
EOF
sh-5.0$ chmod +x test-script.sh
sh-5.0$ cat > Containerfile.test <<EOF
FROM fedora:33
RUN ls -l /test-script.sh
RUN /test-script.sh "Hello world"
RUN dnf update -y | tee /output/update-output.txt
RUN dnf install -y gcc
EOF
sh-5.0$ mkdir output
````
And finally build the image, testing that everything works as expected:
````console
sh-5.0$ buildah -v /home/build/output:/output:rw -v /home/build/test-script.sh:/test-script.sh:ro bud -t myimage -f Containerfile.test
STEP 1: FROM fedora:33
Getting image source signatures
Copying blob 453ed60def9c done
Copying config 71d10e102a done
Writing manifest to image destination
Storing signatures
STEP 2: RUN ls -l /test-script.sh
-rwxr-xr-x. 1 root root 34 Jul 8 07:47 /test-script.sh
STEP 3: RUN /test-script.sh "Hello world"
Args Hello world
total 8
lrwxrwxrwx. 1 root root 7 Jan 28 18:30 bin -> usr/bin
dr-xr-xr-x. 2 root root 6 Jan 28 18:30 boot
drwxr-xr-x. 5 nobody nobody 360 Jul 8 07:39 dev
drwxr-xr-x. 42 root root 4096 Jul 7 09:07 etc
drwxr-xr-x. 2 root root 6 Jan 28 18:30 home
lrwxrwxrwx. 1 root root 7 Jan 28 18:30 lib -> usr/lib
lrwxrwxrwx. 1 root root 9 Jan 28 18:30 lib64 -> usr/lib64
drwx------. 2 root root 6 Jul 7 09:06 lost+found
drwxr-xr-x. 2 root root 6 Jan 28 18:30 media
drwxr-xr-x. 2 root root 6 Jan 28 18:30 mnt
drwxr-xr-x. 2 root root 6 Jan 28 18:30 opt
drwxr-xr-x. 2 root root 6 Jul 8 07:46 output
dr-xr-xr-x. 311 nobody nobody 0 Jul 8 07:39 proc
dr-xr-x---. 2 root root 196 Jul 7 09:07 root
drwxr-xr-x. 3 root root 42 Jul 8 07:47 run
lrwxrwxrwx. 1 root root 8 Jan 28 18:30 sbin -> usr/sbin
drwxr-xr-x. 2 root root 6 Jan 28 18:30 srv
dr-xr-xr-x. 13 nobody nobody 0 Jul 5 17:57 sys
-rwxr-xr-x. 1 root root 34 Jul 8 07:47 test-script.sh
drwxrwxrwt. 2 root root 32 Jul 7 09:07 tmp
drwxr-xr-x. 12 root root 144 Jul 7 09:07 usr
drwxr-xr-x. 18 root root 235 Jul 7 09:07 var
STEP 4: RUN dnf update -y | tee /output/update-output.txt
Fedora 33 openh264 (From Cisco) - x86_64 817 B/s | 5.1 kB 00:06
Fedora - Modular Rawhide - Developmental packag 3.0 MB/s | 3.1 MB 00:01
Fedora - Rawhide - Developmental packages for t 19 MB/s | 72 MB 00:03
Dependencies resolved.
Nothing to do.
Complete!
STEP 5: RUN dnf install -y gcc
Last metadata expiration check: 0:00:30 ago on Wed Jul 8 07:48:12 2020.
Dependencies resolved.
==================================================================================================================================================================================================================================================
Package Architecture Version Repository Size
==================================================================================================================================================================================================================================================
Installing:
gcc x86_64 10.1.1-2.fc33 rawhide 30 M
Installing dependencies:
binutils x86_64 2.34.0-7.fc33 rawhide 5.4 M
binutils-gold x86_64 2.34.0-7.fc33 rawhide 857 k
cpp x86_64 10.1.1-2.fc33 rawhide 9.3 M
glibc-devel x86_64 2.31.9000-17.fc33 rawhide 1.0 M
glibc-headers-x86 noarch 2.31.9000-17.fc33 rawhide 472 k
isl x86_64 0.16.1-10.fc32 rawhide 872 k
kernel-headers x86_64 5.8.0-0.rc4.git0.1.fc33 rawhide 1.2 M
libmpc x86_64 1.1.0-8.fc32 rawhide 59 k
libxcrypt-devel x86_64 4.4.16-5.fc33 rawhide 31 k
Transaction Summary
==================================================================================================================================================================================================================================================
Install 10 Packages
Total download size: 49 M
Installed size: 147 M
Downloading Packages:
(1/10): binutils-gold-2.34.0-7.fc33.x86_64.rpm 3.3 MB/s | 857 kB 00:00
(2/10): binutils-2.34.0-7.fc33.x86_64.rpm 16 MB/s | 5.4 MB 00:00
(3/10): cpp-10.1.1-2.fc33.x86_64.rpm 9.3 MB/s | 9.3 MB 00:01
(4/10): gcc-10.1.1-2.fc33.x86_64.rpm 33 MB/s | 30 MB 00:00
(5/10): glibc-devel-2.31.9000-17.fc33.x86_64.rpm 1.2 MB/s | 1.0 MB 00:00
(6/10): glibc-headers-x86-2.31.9000-17.fc33.noarch.rpm 2.6 MB/s | 472 kB 00:00
(7/10): isl-0.16.1-10.fc32.x86_64.rpm 12 MB/s | 872 kB 00:00
(8/10): kernel-headers-5.8.0-0.rc4.git0.1.fc33.x86_64.rpm 11 MB/s | 1.2 MB 00:00
(9/10): libmpc-1.1.0-8.fc32.x86_64.rpm 534 kB/s | 59 kB 00:00
(10/10): libxcrypt-devel-4.4.16-5.fc33.x86_64.rpm 589 kB/s | 31 kB 00:00
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total 35 MB/s | 49 MB 00:01
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Preparing : 1/1
Installing : binutils-gold-2.34.0-7.fc33.x86_64 1/10
Installing : binutils-2.34.0-7.fc33.x86_64 2/10
Running scriptlet: binutils-2.34.0-7.fc33.x86_64 2/10
Installing : libmpc-1.1.0-8.fc32.x86_64 3/10
Installing : cpp-10.1.1-2.fc33.x86_64 4/10
Installing : kernel-headers-5.8.0-0.rc4.git0.1.fc33.x86_64 5/10
Installing : isl-0.16.1-10.fc32.x86_64 6/10
Installing : glibc-headers-x86-2.31.9000-17.fc33.noarch 7/10
Installing : libxcrypt-devel-4.4.16-5.fc33.x86_64 8/10
Installing : glibc-devel-2.31.9000-17.fc33.x86_64 9/10
Installing : gcc-10.1.1-2.fc33.x86_64 10/10
Running scriptlet: gcc-10.1.1-2.fc33.x86_64 10/10
Verifying : binutils-2.34.0-7.fc33.x86_64 1/10
Verifying : binutils-gold-2.34.0-7.fc33.x86_64 2/10
Verifying : cpp-10.1.1-2.fc33.x86_64 3/10
Verifying : gcc-10.1.1-2.fc33.x86_64 4/10
Verifying : glibc-devel-2.31.9000-17.fc33.x86_64 5/10
Verifying : glibc-headers-x86-2.31.9000-17.fc33.noarch 6/10
Verifying : isl-0.16.1-10.fc32.x86_64 7/10
Verifying : kernel-headers-5.8.0-0.rc4.git0.1.fc33.x86_64 8/10
Verifying : libmpc-1.1.0-8.fc32.x86_64 9/10
Verifying : libxcrypt-devel-4.4.16-5.fc33.x86_64 10/10
Installed:
binutils-2.34.0-7.fc33.x86_64 binutils-gold-2.34.0-7.fc33.x86_64 cpp-10.1.1-2.fc33.x86_64 gcc-10.1.1-2.fc33.x86_64 glibc-devel-2.31.9000-17.fc33.x86_64 glibc-headers-x86-2.31.9000-17.fc33.noarch
isl-0.16.1-10.fc32.x86_64 kernel-headers-5.8.0-0.rc4.git0.1.fc33.x86_64 libmpc-1.1.0-8.fc32.x86_64 libxcrypt-devel-4.4.16-5.fc33.x86_64
Complete!
STEP 6: COMMIT myimage
Getting image source signatures
Copying blob fd46c60e883a skipped: already exists
Copying blob f3157b126b5d done
Copying config d3a341d4fd done
Writing manifest to image destination
Storing signatures
--> d3a341d4fd9
d3a341d4fd993fb4ee84f102e5915fe9ab544f4cd72fd9947beec9e745f12302
sh-5.0$ buildah images
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/myimage latest d3a341d4fd99 22 seconds ago 475 MB
registry.fedoraproject.org/fedora 33 71d10e102a30 23 hours ago 191 MB
sh-5.0$ ls -l output/
total 4
-rw-r--r--. 1 build build 288 Jul 8 07:48 update-output.txt
````

5
docs/tutorials/README.md
View File

@@ -19,3 +19,8 @@ Learn how Buildah can use the ONBUILD instruction in either a Dockerfile or via
**[Include Buildah in your build tool](04-include-in-your-build-tool.md)**
Learn how to include Buildah as a library in your build tool.
**[Rootless OpenShift container](05-openshift-rootless-bud.md)**
Learn how to build an image from a rootless OpenShift container.