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Balena base images

Balenalib is the central home for 26000+ IoT focused Docker images built specifically for balenaCloud and balenaOS. This set of images provide a way to get up and running quickly and easily, while still providing the option to deploy slim secure images to the edge when you go to production.

Supported Architectures, Distros and Languages

Currently, balenalib supports the following OS distributions and Language stacks. If you would like to see others added, create an issue on the balena base images repo.

  • Multiple Architectures:
    • amd64
    • aarch64
    • armv7hf
    • i386
    • rpi
  • Multiple Distributions
    • Debian: bullseye (latest), bookworm, buster, sid
    • Fedora: 37 (latest), 38
    • Ubuntu: noble (latest), jammy, focal, xenial, bionic
    • Alpine: 3.20 (latest), 3.19, 3.18, 3.17, 3.16, 3.15, 3.14, 3.13, 3.12, edge
  • Multiple language stacks:
    • Node: 20.12.0, 19.6.1 (latest), 18.14.1
    • Python: 3.11.2 (latest), 3.10.10, 3.9.16, 3.8.16
    • Openjdk: 11-jdk, 11-jre, 17-jdk, 16-jdk
    • Golang: 1.20.1 (latest), 1.19.6, 1.18.10
    • Dotnet: 7.0-sdk, 7.0-runtime, 7.0-aspnet, 6.0-sdk, 6.0-runtime, 6.0-aspnet

Features Overview

How to Pick a Base Image

When starting out a project, it's generally easier to have a "fatter" image, which contains a lot of prebuilt dependencies and tools. These images help you get setup faster and work out the requirements for your project. For this reason, it's recommended to start with -build variants, and as your project progresses, switch to a -run variant with some docker multistage build magic to slim your deploy image down. In most cases, your project can just use a Debian based distribution, which is the default if not specified, but if you know the requirements of your project or prefer specific distros, Ubuntu, Alpine, and Fedora images are available. The set of balenalib base images follow a simple naming scheme described below, which will help you select a base image for your specific needs.

How the Image Naming Scheme Works

With over 26000 balenalib base images to choose from, it can be overwhelming to decide which image and tag are correct for your project. To pick the correct image, it helps to understand how the images are named as that indicates what is installed in the image. In general, the naming scheme for the balenalib image set follows the pattern below:

balenalib/<hw>-<distro>-<lang_stack>:<lang_ver>-<distro_ver>-(build|run)-<yyyymmdd>

Image Names

  • <hw> is either architecture or device type and is mandatory. If you are using Dockerfile.template, you can replace <hw> with %%BALENA_MACHINE_NAME%% or %%BALENA_ARCH%%. Images named with device type are built using base images named with architecture. The %%BALENA_MACHINE_NAME%% base images are bigger and include more tools. Check example for reference. Check the list of available base images for device names and architectures.
  • <distro> is the Linux distribution. Currently there are 4 distributions, namely Debian, Alpine, Ubuntu and Fedora. This field is optional and will default to Debian if left out.
  • <lang_stack> is the programming language pack, currently we support Node.js, Python, OpenJDK, .Net, and Go. This field is optional, and if left out, no language pack will be installed, so you will just have the distribution and you can later install and use any language in your image/container.

Image Tags

In the tags, all of the fields are optional, and if they are left out, they will default to their latest pointer.

  • <lang_ver> is the version of the language stack, for example, Node.js 20.12.0, it can also be substituted for latest.
  • <distro_ver> is the version of the Linux distro, for example Debian and it's valid version as mentioned above in the list.
  • For each combination of distro and stack, we have two variants called run and build. The build variant is much heavier as it has a number of tools preinstalled to help with building source code. You can see an example of the tools that are included in the Debian variants. Navigate to the Distro version you are looking for and find the build and run variants of the image. The run variants are stripped down and only include a few useful runtime tools. If no variant is specified, the image defaults to run.
  • The last optional field on tags is the date tag <yyyymmdd>. If a date tag is specified, the pinned release will always be pulled from Docker Hub, even if there is a new one available.

Note: Pinning to a date-frozen base image is highly recommended if you are running a fleet in production. This ensures that all your dependencies have a fixed version and won't get randomly updated until you decide to pin the image to a newer release.

Examples

balenalib/raspberrypi3-node:10.18

  • <hw> : raspberrypi3 - The Raspberry Pi 3 device type.
  • <distro> : omitted, so it defaults to Debian.
  • <lang> : node - the Node.js runtime and npm will be installed
  • <lang_ver> : 10.18 - This gives us Node.js version 10.18.x whatever is the latest patch version provided on balenalib
  • <distro_ver> : omitted, so it defaults to buster
  • (build|run) : omitted, so the image defaults to the slimmed down run variant
  • <yyyymmdd> : omitted, we don't have a date frozen image, so new updates pushed to our 10.18 tag, for example patch versions from Node.js will automatically be inherited when they are available.

balenalib/i386-ubuntu-python:latest-bionic-build-20191029

  • <hw> : i386 - the intel 32 bit architecture that runs on Intel Edison
  • <distro> : ubuntu
  • <lang> : python
  • <lang_ver> : latest points to the latest Python 2 version, which currently is 2.7.17
  • <distro_ver> : bionic is Ubuntu 18.04
  • (build|run) : build - to include things like build-essential and gcc
  • <yyyymmdd> : 20191029 is a date frozen image - so this image will never be updated on Docker Hub.

run vs. build

For each combination of <hw>-<distro>-<lang> there is both a run and a build variant. These variants are provided to allow for easier multistage builds.

The run variant is designed to be a slim and minimal variant with only runtime essentials packaged into it. To find what packages exactly, navigate to the Debian version and check the Dockerfile inside the run folder.

The build variant is a heavier image that includes many of the tools required for building from source such as build-essential, gcc, etc. As an example, you can see the types of packages installed in the balenalib/armv7hf-debian:build variant on the balena-io-library/base-images repository.

These variants make building multistage projects easier, take for example, installing an I2C node.js package, which requires a number of build time dependencies to build the native i2c node module, but we don't want to send all of those down to our device. This is the perfect time for multistage builds and to use the build and run variants.

FROM balenalib/raspberrypi3-debian-node:latest-bookworm-build as build
RUN npm install --only=production i2c

# The run time container that will go to devices
FROM balenalib/raspberrypi3-debian-node:latest-bookworm-run

# Grab our node modules for the build step
COPY --from=build ./node_modules ./node_modules
COPY main.js main.js

CMD ["node", "main.js"]

Notes

Devices with a device type of raspberry-pi (Raspberry Pi1 and Zero) will be built from balenalib/rpi-raspbian and will be Raspbian base images. The raspberry-pi2 and raspberrypi3 device types Debian base images have the Raspbian package source added, and Raspbian userland pre-installed.

Not all OS distro and language stack versions are compatible with each other. Notice that there are some combinations that are not available in the balenalib base images.

  • Node.js dropped 32-bit builds a while ago so i386-based nodejs images (Debian, Fedora and Ubuntu) v8.x and v6.x are official. New series (v10.x and v12.x) are using unofficial builds.
  • armv6 binaries were officially dropped from Node.js v12 and v12 armv6 support is now considered unofficial.
  • The Node.js v6.x and v8.x series are not available for i386 Alpine Linux base images v3.9 and edge as node crashes with segfault error, we are investigating the issue and will add them back as soon as the issue is resolved.

Installing Packages

Installing software packages in balenalib containers is very easy, and in most cases, you can just use the base image operating system package manager. However to make things even easier, every balenalib image includes a small install_packages script that abstracts away the specifics of the underlying package managers, and adds the following useful features:

  • Install the named packages, skipping prompts etc.
  • Clean up the package manager metadata afterward to keep the resulting image small.
  • Retries if package install fails. Sometimes a package will fail to download due to a network issue, and retrying may fix this, which is particularly useful in an automated build pipeline.

An example of this in action is as follows:

FROM balenalib/raspberrypi3

RUN install_packages wget git

CMD ["bash", "start.sh"]

This will run an apt-get update -qq, then install wget and git via apt-get with -y --no-install-recommends flags, and it will by default try this 2 times before failing. Checkout the Dockerfile to find the source install_packages by navigating to the Debian version you want, selecting run or build folder and click Dockerfile

How the Images Work at Runtime

Each balenalib base image has a default ENTRYPOINT which is defined as ENTRYPOINT ["/usr/bin/entry.sh"]. This ensures that entry.sh is run before your code defined in CMD of your Dockerfile.

On container startup, the entry.sh script first checks if the UDEV flag is set to true or false. In the case where it is false, the CMD is then executed. In the case it is true (or 1), the entry.sh will check if the container is running privileged, if it is, it will mount /dev to a devtmpfs and then start udevd. In the case the container is an unprivileged container, no mount will be performed, and udevd will be started (although it won't be very much use without the privilege).

At the end of a container's lifecycle, when a request to container restart, reboot or shutdown is sent to the supervisor, the balenaEngine will send a SIGTERM (signal 15) to the containers, and 10 seconds later it will issue a SIGKILL if the container is still running. This timeout can also be configured via the stop_grace_period in your docker-compose.yml.

Working with Dynamically Plugged Devices

In many IoT projects, your containers will want to interact with some hardware, often this hardware is plugged in at runtime, in the case of USB or serial devices. In these cases, you will want to enable udevd in your container. In balenalib images this can easily be done either by adding ENV UDEV=1 in your Dockerfile or by setting an environment variable using variables.

You will also need to run your container privileged. By default, any balenaCloud projects that don't contain a docker-compose.yml will run their containers privileged. If you are using a multicontainer project, you will need to add privileged: true to each of the service definitions for the services that need hardware access.

When a balenalib container runs with UDEV=1 it will first detect if it is running on a privileged container. If it is, it will mount the host OS /dev to a devtmpfs and then start udevd. Now anytime a new device is plugged in, the kernel will notify the container udevd daemon and the relevant device nodes in the container /dev will appear.

Note: The new balenalib base images make sure udevd runs in its own network namespace, so as to not interfere with cellular modems. These images should not have any of the past udev restrictions of the resin/ base images.

Major Changes

When moving from the legacy resin/... base images to the balenalib ones, there are a number of breaking changes that you should take note of, namely:

  • UDEV now defaults to off, so if you have code that relies on detecting dynamically plugged devices, you will need to enable this in either your Dockerfile or via a device environment variable. See Working with Dynamically Plugged Devices.
  • The INITSYSTEM functionality has been completely removed, so containers that rely on systemd or openRC should install and set up the initsystem in their apps. See Installing your own Initsystem.
  • Mounting of /dev to a devtmpfs will now only occur when UDEV=on and the container is running as privileged. 1, true and on are valid value for UDEV and will be evaluated as UDEV=on, all other values will turn UDEV off.
  • Support for Debian Wheezy has been dropped.
  • armel architecture has been renamed to armv5e.

Installing your own Initsystem

Since the release of multicontainer on the balenaCloud platform, we now recommend the use of multiple containers and no longer recommend the use of an initsystem, particularly systemd, in the container as it tends to cause a myriad of issues, undefined behavior and requires the container to run fully privileged.

However, if your container relies on initsystem features, it is fairly easy to add this functionality to a balenalib base image. We have provided some examples for systemd and openRC. Please note that different systemd versions require different implementation so for Debian Jessie and older, please refer to this example and for Debian Stretch and later, please refer to this example.

Generally, for systemd, it just requires installing the systemd package, masking a number of services and defining a new entry.sh and a balena.service. The Dockerfile below demonstrates this:

FROM balenalib/amd64-debian:buster

# Install Systemd
RUN apt-get update && apt-get install -y --no-install-recommends \
        systemd \
        systemd-sysv \
    && rm -rf /var/lib/apt/lists/*

ENV container docker

# We never want these to run in a container
# Feel free to edit the list but this is the one we used
RUN systemctl mask \
    dev-hugepages.mount \
    sys-fs-fuse-connections.mount \
    sys-kernel-config.mount \

    display-manager.service \
    getty@.service \
    systemd-logind.service \
    systemd-remount-fs.service \

    getty.target \
    graphical.target \
    kmod-static-nodes.service

COPY entry.sh /usr/bin/entry.sh
COPY balena.service /etc/systemd/system/balena.service

RUN systemctl enable /etc/systemd/system/balena.service

STOPSIGNAL 37
ENTRYPOINT ["/usr/bin/entry.sh"]

##################################
# Your code here...
##################################

Building ARM Containers on x86 Machines

This is a unique feature of balenalib ARM base images that allows you to run them anywhere (running ARM image on x86/x86_64 machines). A tool called resin-xbuild and QEMU are installed inside any balenalib ARM base image and can be triggered by RUN ["cross-build-start"] and RUN ["cross-build-end"]. QEMU will emulate any instructions between cross-build-start and cross-build-end. So this Dockerfile:

FROM balenalib/armv7hf-debian

RUN [ "cross-build-start" ]

RUN apt-get update
RUN apt-get install python-pip
RUN pip install virtualenv

RUN [ "cross-build-end" ]

can run on your x86 machine and there will be no Exec format error, which is the error when you run an ARM binary on x86. This approach works only if the image is being built on x86 systems. Use the --emulated flag in balena push to trigger a qemu emulated build targeting the x86 architecture. More details can be found in our blog post here. You can find the full source code for the two cross-build scripts here.