History: atomic upgrade

By atomic upgrade, we mean:
* Put Tiki in read-only
* Make an exact copy
* Upgrade the copy
* Swap the two (rename or symlink directories)
** No downtime
** Easily rollback (if the database structure remains the same)

!! Symlink approach

This might be an option Tiki-Manager can automate.

Supposing all sites are stored on -+ /data/www +-, a new site having the domain __tiki.vbox__ will be stored at -+ /data/www/tiki.vbox +-. The folder structure for this site will be

{CODE()}
/data/www/tiki.vbox
├── conf
│   ├── local.ini
│   └── local.php
├── html -> releases/20200227
├── logs
│   ├── httpd-access.log
│   └── httpd-error.log
└── releases
│   └── 20200227
│       └── db
│           └── local.php -> ../../../conf/local.php
└── data
    ├── img
    ├── modules
    └── temp
{CODE}

!!! The -+ conf +- folder

In this folder should exists at least the __local.php__ file, that contains credentials for database access. Optionally, it might contains __local.ini__ file, that contains overrides for tiki preferences. 

!!! The -+ logs +- folder

Contains any log files. Usually, it holds webserver logs in it, but it might be a good idea put Tiki logs there.

!!! The -+ releases +-  folder

Contains one or more Tiki installation. Each subfolder is a Tiki installation and the subfolder name is related to Tiki version or to the installation date.

!!! The -+ html +- link

The html is the document root for the webserver. It should point to the latest Tiki installation on -+ releases +- folder.

!!! The -+ data +- folder

Should have in folders Tiki needs to work properly.

* vendor
* temp
* img/wiki
* img/wiki_up

!!! Secrets to make it works

1) You need to symlink local.php from -+ db/local.php +- to the one in the conf folder

{CODE()}
cd /data/www/tiki.vbox
ln -rs conf/local.php html/db/local.php
{CODE}

2) Tiki installations should have composer dependencies installed

3) Tiki installations should have permissions correctly set.

4) The data folder should be linked into Tiki structure

{CODE()}
cd /data/www/tiki.vbox/

# data files
mkdir -p data/{img,modules}
mv html/img/trackers data/img
mv html/img/wiki data/img
mv html/img/wiki_up data/img
mv html/storage data/
ln -rTsf data/img/trackers   html/img/trackers
ln -rTsf data/img/wiki       html/img/wiki
ln -rTsf data/img/wiki_up    html/img/wiki_up
ln -rTsf data/storage   html/storage

# custom packages
mv html/vendor data/vendor
[ -f "html/composer.json" ] && mv html/composer.json data/composer.json
ln -rTsf data/vendor    html/vendor
ln -rsf data/composer.json html/composer.json

# temp files
mv html/modules/cache data/modules
mv html/temp data/
ln -rTsf data/modules/cache  html/modules/cache
ln -rTsf data/temp           html/temp
{CODE}

!!! Steps to update tiki

1) Copy the new tiki installation to -+ releases +- folder
2) Ensure composer deps are installed
3) Ensure permissions are correctly set
4) Ensure the +- /data/www/tiki.vbox/html/db/local.php +- points to -+ /data/www/tiki.vbox/conf/local.php +-
5) Make -+ html +- symlink point to the new tiki installation

{CODE()}
ln -Tsf releases/new  html
{CODE}

!!! Steps to rollback

Point -+ html +- symlink to previous selected Tiki installation.

{CODE()}
ln -Tsf releases/old  html
{CODE}

!!! Concernings

* Tiki writes a lot of files in a lot of different folders. It is possible there is more folders to symlink
* The amount of necessary links make it complex to automate
* Keeping many installation on -+releases+- folder will take a lot of disk space
* On Windows might not be possible this approach
* Custom translations is not covered and will be lost in a upgrade

!!! References

* https://roots.io/trellis/ playbooks


We want this for ((Tiki Manager)) and for ((Docker))