Docker installation using official guide

Introduction

Hello,
I'm a newbie in using Owncloud technology, I installed it on docker using this official guide https://doc.owncloud.org/server/10.0/admin_manual/installation/docker/ and there are few things I don't understand, so here are my question, I will be grateful to any answer.

Questions

  1. Everytime I stop/start or down/up the trio owncloud/mariadb/redis using docker-compose and I go back the gui, It asks me to define admin user such as it was the first time I launch it. No problem with the data persistence, files and folder are saved.
    2.By default, the installation select SQLITE as database type but the installation assume that we use mariadb instead, should I select mariadb in the database type? Selecting mariadb give me this error: Error while trying to create admin user: Failed to connect to the database: An exception occured in driver: SQLSTAT[HY000][220] No such file or directory.
    3.When I down/up the trio using docker-compose, I loose all extra apps such as calendar or gallery. Is it possible to keep the persistence?
    4.I tried to add a local folder as an external storage but following this guide don't work: https://doc.owncloud.org/server/10.0/admin_manual/configuration/files/external_storage/local.html. Travelling the github yesterday I understood that this feature was not available anymore fore security reason, Am I right?

Operating system:
CentOS Linux 7 (Core)
CPE OS Name: cpe:/o:centos:centos:7
Kernel: Linux 3.10.0-327.el7.x86_64
Architecture: x86-64

Database:
webhippie/mariadb
used with:
webhippie/redis

ownCloud version: (see ownCloud admin page)
owncloud/server:10.0.4

Updated from an older ownCloud or fresh install:

The content of config/config.php:
{
"system": {
"passwordsalt": "REMOVED SENSITIVE VALUE",
"secret": "REMOVED SENSITIVE VALUE",
"trusted_domains": [
"192.168.0.11"
],
"datadirectory": "\/mnt\/data\/files",
"overwrite.cli.url": "http:\/\/192.168.0.11",
"dbtype": "sqlite3",
"version": "10.0.4.4",
"dbname": "owncloud",
"dbhost": "localhost",
"dbtableprefix": "oc_",
"mysql.utf8mb4": true,
"dbuser": "REMOVED SENSITIVE VALUE",
"dbpassword": "REMOVED SENSITIVE VALUE",
"instanceid": "ocbhyy3g4bcc",
"logtimezone": "UTC",
"installed": true
}
}

Client configuration

Vivaldi 1.10.867.38 (Stable channel) (32-bit)

Operating system:
Windows 7 Pro 64bits

You'll likely need to provide more information in the .env file described in https://doc.owncloud.org/server/10.0/admin_manual/installation/docker/ . I think the full list of options is in https://github.com/owncloud-docker/base#available-environment-variables

For the app persistence, as long as the docker volume is properly mapped in the host it should work. It might not be properly mapped by default

Local storage should be working fine. There is a switch in the config.php file 'files_external_allow_create_new_local' => false, (check the config.sample.php file for more info). This is disabled by default due to security reason, as you've said, so enable the feature with caution.