Ability to run as a non-root user and / or with persisted volumes

[ptr727]

When running as a non-root user, container fails to start due to permission problems with /etc/postfix.
When mounting /etc/postfix and /var/spool/postfix, the container fails due to /etc/postfix/main.cf not existing.

Suggestions:

• Copy default main.cf if target does not exist.
• touch main.cf to ensure it exists.
• Set permissions such that a non-root user can be used.

Prep:

#!/bin/bash

set -ea && source .env && set +a

function create_dir() {

    local root_dir="$1"
    shift
    local sub_dirs=("$@")

    echo "Creating : \"$root_dir\""
    sudo mkdir -p "$root_dir"

    for sub_dir in "${sub_dirs[@]}";
    do
        echo "Creating : \"$root_dir/$sub_dir\""
        sudo mkdir -p "$root_dir/$sub_dir"
    done

    echo "Setting ownership to : \"${USER_NONROOT_NAME}:${USERS_GROUP_NAME}\""
    sudo chown -R ${USER_NONROOT_NAME}:${USERS_GROUP_NAME} "$root_dir"
    sudo chmod -R ugo=rwx "$root_dir"
}

create_dir "${APPDATA_DIR}/postfix" "config" "spool"
sudo touch "${APPDATA_DIR}/postfix/config/main.cf"
create_dir "${APPDATA_DIR}/postfix" "config" "spool"

Compose:

  postfix:
    image: docker.io/juanluisbaptiste/postfix:latest
    container_name: postfix
    hostname: smtp
    domainname: ${DOMAIN_NAME}
    restart: unless-stopped
    user: ${USER_NONROOT_ID}:${USERS_GROUP_ID}
    environment:
      - TZ=${TZ}
      - SERVER_HOSTNAME=smtp.${DOMAIN_NAME}
      - SMTP_SERVER=$EXTERNAL_SMTP_SERVER
      - SMTP_PORT=$EXTERNAL_SMTP_PORT
      - SMTP_USERNAME=${EXTERNAL_SMTP_USERNAME}
      - SMTP_PASSWORD_FILE=/run/secrets/external_smtp_password
      - DEBUG=yes
    volumes:
      - ${APPDATA_DIR}/postfix/config:/etc/postfix
      - ${APPDATA_DIR}/postfix/spool:/var/spool/postfix
    networks:
      public_network:
        priority: 1000
        ipv4_address: ${SMTP_IP}
      local_network:
    secrets:
      - external_smtp_password