The setup.sh script is the core of all the cloud based installation options. Regarding an image-based installation, you don't have to dive into the details of this script, but if you want to install Redash manually (or are just curious about the internals), it's better to take a quick look at it.

Let's break the script into parts while going over it.

At first, we set Redash base installation path, and start defining helper functions.

The following is the definition of helper function, which installs the docker compose as well as surrounding components:

#!/usr/bin/env bash
# This script setups dockerized Redash on Ubuntu 18.04.
set -eu

REDASH_BASE_PATH=/opt/redash

install_docker(){
    # Install Docker
    sudo apt-get update 
    sudo apt-get -yy install apt-transport-https ca-certificates curl software-properties-common wget pwgen
    curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
    sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
    sudo apt-get update && sudo apt-get -y install docker-ce

    # Install Docker Compose
    sudo curl -L https://github.com/docker/compose/releases/download/1.22.0/docker-compose-$(uname -s)-$(uname -m) -o /usr/local/bin/docker-compose
    sudo chmod +x /usr/local/bin/docker-compose

    # Allow current user to run Docker commands
    sudo usermod -aG docker $USER
    newgrp docker
}

The following is a helper function that creates the directories for Redash installation: 

create_directories() {
    if [[ ! -e $REDASH_BASE_PATH ]]; then
        sudo mkdir -p $REDASH_BASE_PATH
        sudo chown $USER:$USER $REDASH_BASE_PATH
    fi

    if [[ ! -e $REDASH_BASE_PATH/postgres-data ]]; then
        mkdir $REDASH_BASE_PATH/postgres-data
    fi
}

The following is a helper function that creates and persists Environment Variables used in Redash:

create_config() {
    if [[ -e $REDASH_BASE_PATH/env ]]; then
        rm $REDASH_BASE_PATH/env
        touch $REDASH_BASE_PATH/env
    fi

    COOKIE_SECRET=$(pwgen -1s 32)
    POSTGRES_PASSWORD=$(pwgen -1s 32)
    REDASH_DATABASE_URL="postgresql://postgres:${POSTGRES_PASSWORD}@postgres/postgres"

    echo "PYTHONUNBUFFERED=0" >> $REDASH_BASE_PATH/env
    echo "REDASH_LOG_LEVEL=INFO" >> $REDASH_BASE_PATH/env
    echo "REDASH_REDIS_URL=redis://redis:6379/0" >> $REDASH_BASE_PATH/env
    echo "POSTGRES_PASSWORD=$POSTGRES_PASSWORD" >> $REDASH_BASE_PATH/env
    echo "REDASH_COOKIE_SECRET=$COOKIE_SECRET" >> $REDASH_BASE_PATH/env
    echo "REDASH_DATABASE_URL=$REDASH_DATABASE_URL" >> $REDASH_BASE_PATH/env
}

The following helper function fetches the latest docker image, as well as docker-compose file, and runs it:

setup_compose() {
    REQUESTED_CHANNEL=stable
    LATEST_VERSION=`curl -s "https://version.redash.io/api/releases?channel=$REQUESTED_CHANNEL"  | json_pp  | grep "docker_image" | head -n 1 | awk 'BEGIN{FS=":"}{print $3}' | awk 'BEGIN{FS="""}{print $1}'`

    cd $REDASH_BASE_PATH
    REDASH_BRANCH="${REDASH_BRANCH:-master}" # Default branch/version to master if not specified in REDASH_BRANCH env var
    wget https://raw.githubusercontent.com/getredash/redash/${REDASH_BRANCH}/setup/docker-compose.yml
    sed -ri "s/image: redash/redash:([A-Za-z0-9.-]*)/image: redash/redash:$LATEST_VERSION/" docker-compose.yml
    echo "export COMPOSE_PROJECT_NAME=redash" >> ~/.profile
    echo "export COMPOSE_FILE=/opt/redash/docker-compose.yml" >> ~/.profile
    source ~/.profile
    docker-compose run --rm server create_db
    docker-compose up -d
}

The following code invokes all the previously defined functions (the order here is important):

install_docker
create_directories
create_config
setup_compose