mikenye / deploy-s6-overlay

Helper script to deploy justcontainers/s6-overlay regardless of architecture

deploy-s6-overlay

deploy-s6-overlay.sh is a helper script to deploy s6-overlay to multi-architecture containers.

Prevents the need for per-architecture Dockerfiles, and allows all s6-overlay deployment tasks to be done within a single layer.

Prerequisites

• file
• gnupg or gnupg2
• curl or wget (and also ca-certificates if not installed already)

Note regarding verification & version of s6-overlay

s6-overlay version 3.0.0.0 has just been released! Well done to the s6-overlay dev team.

As the s6-overlay dev team work to update their CI actions to support this new version, currently:

• s6-overlay is temporarily no longer signed by gpg, and thus verification of downloads by this script has been temporarily disabled.
• Pre-built binaries for version 3.0.0.0 are not yet available, and thus this script will download v2.2.0.3 (unless the user specifies another version, v3.0.0.0 will fail until binaries are released)

When the s6-overlay team update their CIs, I'll revert the script back to normal behaviour.

How it works

Originally the script would use uname -m to determine the container architecture, however this method has been abandoned. If cross-building (ie: building for i386 on amd64), you'd get the wrong architecture, as uname -m would return amd64.

Now, file is used on itself, which returns the installed architecture of the file binary. The returned architecture is then used to determine what architecture of s6 overlay to be installed. See below for examples.

The pre-requisites (file, gnupg/gnupg2, curl/wget) can be installed and removed in the same layer, preventing unnecessary image bloat.

The script also includes testing to make sure the binaries run properly after installation. If there are any problems, the image will exit abnormally, which should cause the docker build process to fail (instead of returning a non-working image).

Architecture examples

x86

Example output on Alpine:

/usr/bin/file: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-i386.so.1, stripped

Example output on Debian

/usr/bin/file: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=d48e1d621e9b833b5d33ede3b4673535df181fe0, stripped

amd64

Example output on Alpine:

/usr/bin/file: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-x86_64.so.1, stripped

Example output on Debian:

/usr/bin/file: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=6b0b86f64e36f977d088b3e7046f70a586dd60e7, stripped

arm

Example output on Debian:

/usr/bin/file: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=f57b617d0d6cd9d483dcf847b03614809e5cd8a9, stripped

armhf

Example output on Alpine:

/usr/bin/file: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-armhf.so.1, stripped  # /usr/bin/file: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=921490a07eade98430e10735d69858e714113c56, stripped

Example output on Debian:

/usr/bin/file: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=921490a07eade98430e10735d69858e714113c56, stripped

aarch64

Example output on Alpine:

/usr/bin/file: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-aarch64.so.1, stripped

Example output on Debian:

/usr/bin/file: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, for GNU/Linux 3.7.0, BuildID[sha1]=a8d6092fd49d8ec9e367ac9d451b3f55c7ae7a78, stripped

Using

Ensure you have file, gnupg/gnugp2, wget/curl and ca-certificates available.

In your project's Dockerfile, add one of the following early on within a RUN instruction:

curl -o /tmp/deploy-s6-overlay.sh -s https://raw.githubusercontent.com/mikenye/deploy-s6-overlay/master/deploy-s6-overlay.sh && \
sh /tmp/deploy-s6-overlay.sh && \
rm /tmp/deploy-s6-overlay.sh && \

or:

wget -q -O /tmp/deploy-s6-overlay.sh https://raw.githubusercontent.com/mikenye/deploy-s6-overlay/master/deploy-s6-overlay.sh && \
sh /tmp/deploy-s6-overlay.sh && \
rm /tmp/deploy-s6-overlay.sh && \

Both of the above methods achieve the same thing.

After s6-overlay installation, if they are not needed in your image, you may remove file, gnupg/gnugp2, wget/curl and ca-certificates.

At the end of the Dockerfile, you'll also need to include:

ENTRYPOINT [ "/init" ]

...in order for s6 to be initialised during container start.

Examples follow:

Example for alpine

...
FROM alpine:latest
RUN ...
    apk add --no-cache file gnupg && \
    wget -q -O - https://raw.githubusercontent.com/mikenye/deploy-s6-overlay/master/deploy-s6-overlay.sh | sh && \
    apk del --no-cache file gnupg && \
    ...
ENTRYPOINT [ "/init" ]
...

Note, Alpine includes wget so this is not explicitly installed.

Example for debian:stable-slim

...
FROM debian:stable-slim
RUN ...
    apt-get install --no-install-recommends -y \
        ca-certificates \
        curl \
        file \
        gnupg \
        && \
        curl -s https://raw.githubusercontent.com/mikenye/deploy-s6-overlay/master/deploy-s6-overlay.sh | sh && \
    apt-get remove -y \
        ca-certificates \
        curl \
        file \
        gnupg \
        && \
    apt-get autoremove -y
    ...
ENTRYPOINT [ "/init" ]
...

Environment Variables

The default behaviour of the script can be overridden through the use of environment variables.

Environment Variable	Details
S6OVERLAY_ARCH	If set, overrides architecture detection and will install the architecture specified. Can be set to one of the following: aarch64, amd64, arm, armhf, ppc64le, x86.
S6OVERLAY_VERSION	If set, will install a specific release of s6-overlay (instead of the latest stable). See here for a list of releases.

Testing

This script has been tested with alpine and debian:stable-slim images on all supported architectures.

The script is linted with Shellcheck.

Getting help

Please feel free to open an issue on the project's GitHub.

I also have a Discord channel, feel free to join and converse.