In order to upgrade for all our MediaWiki clusters to Debian Buster, we need to upgrade the current Debian Stretch installation to use ICU 63. The reason is that Debian ships with version 63. This process requires all servers to be upgraded within a short period of time, and after that running the `updateCollation.php` script on all wikis with a non-standard collation.
**Migration day will be Monday, November 16, 2020.**
The transition plan will roughly be as follows:
[x] Rebuild related packages for stretch by linking them to `libicu63` and add them to the `component/icu63` repo
[x] php7.2-bcmath
[x] php7.2-bz2
[x] php7.2-cli
[x] php7.2-common
[x] php7.2-curl
[x] php7.2-dba
[x] php7.2-fpm
[x] php7.2-gd
[x] php7.2-gmp
[x] php7.2-intl
[x] php7.2-json
[x] php7.2-mbstring
[x] php7.2-mysql
[x] php7.2-opcache
[x] php7.2-phpdbg
[x] php7.2-readline
[x] php7.2-xml
[x] php-igbinary
[x] php-apcu-b
[x] php-memcached
[x] php-redis
[x] php-mailparse
[x[ php-mongodb
[x] php-msgpack
[x] dh-php
[x] php-acpu
[x] php-imagick
[x] php-defaults
[x] php-excimer
[x] php-luasandbox
[x] php-geoip
[x] php-wmerrors
[x] tideways
[x] tideways-xhprof
[x] wikidiff2
[x] libxml
[x] Use a feature flag to enable `component/icu63` in puppet
[] Test packages on mwdebug servers
[x] Define a migration date - **16th Nov 2020**
[] Notify the communities (phabricator, wikitech-l, ?) -> T267145
[] On Migration day:
[] Upgrade to libicu63 everywhere
[] Run `updateCollation.php` on all wikis where it's needed (~10 days, this is the point of no return, **use screen/tmux)
(This task originally included the upgrade of MediaWiki servers to Buster, which is why there might be some comments related to that)