Docker is able to build images automatically by reading instructions from a text file called a Dockerfile. Dockerfiles can be layered on top of each other, so to create a Docker Yocto builder image we would start by using a Ubuntu 16.04 Docker image or one of the other supported distributions, and sequentially configure the image.

An example Dockerfile for a Yocto builder follows:

FROM ubuntu:16.04                                                                
MAINTAINER Alex Gonzalez <[email protected]>                               
                                                                                 
# Upgrade system and Yocto Proyect basic dependencies                            
RUN apt-get update && apt-get -y upgrade && apt-get -y install gawk wget git-core diffstat unzip texinfo gcc-multilib build-essential chrpath socat cpio python python3 python3-pip python3-pexpect xz-utils debianutils iputils-ping libsdl1.2-dev xterm curl 
                                                                                 
# Set up locales                                                                 
RUN apt-get -y install locales apt-utils sudo && dpkg-reconfigure locales && locale-gen en_US.UTF-8 && update-locale LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 
ENV LANG en_US.utf8                                                              
                                                                                 
# Clean up APT when done.                                                        
RUN apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*               
                                                                                 
# Replace dash with bash                                                         
RUN rm /bin/sh && ln -s bash /bin/sh                                        
                                                                                 
# User management                                                                
RUN groupadd -g 1000 build && useradd -u 1000 -g 1000 -ms /bin/bash build && usermod -a -G sudo build && usermod -a -G users build 
                                                                                 
# Install repo                                                                   
RUN curl -o /usr/local/bin/repo https://storage.googleapis.com/git-repo-downloads/repo && chmod a+x /usr/local/bin/repo 
                                                                                 
# Run as build user from the installation path                                   
ENV YOCTO_INSTALL_PATH "/opt/yocto"                                              
RUN install -o 1000 -g 1000 -d $YOCTO_INSTALL_PATH                               
USER build                                                                       
WORKDIR ${YOCTO_INSTALL_PATH}                                                    
                                                                                 
# Set the Yocto release                                                          
ENV YOCTO_RELEASE "rocko"                                                         
                                                                                 
# Install Poky                                                                   
RUN git clone --branch ${YOCTO_RELEASE} git://git.yoctoproject.org/poky          
                                                                                 
# Install FSL community BSP                                                      
RUN mkdir -p ${YOCTO_INSTALL_PATH}/fsl-community-bsp && cd ${YOCTO_INSTALL_PATH}/fsl-community-bsp && repo init -u https://github.com/Freescale/fsl-community-bsp-platform -b ${YOCTO_RELEASE} && repo sync 
                                                                                 
# Create a build directory for the FSL community BSP                             
RUN mkdir -p ${YOCTO_INSTALL_PATH}/fsl-community-bsp/build                       
                                                                                 
# Make /home/build the working directory                                         
WORKDIR /home/build