add wait-for-it and get-variable, these will be used to determine the proper address of the database and wait for it to connect

Dockerfile

@@ -12,6 +12,8 @@ RUN chmod +x add_extension.sh
 RUN ./add_extension.sh Scribunto $MEDIAWIKI_BRANCH && \
     ./add_extension.sh VisualEditor $MEDIAWIKI_BRANCH
 
+ADD https://raw.githubusercontent.com/vishnubob/wait-for-it/master/wait-for-it.sh /wait-for-it
 ADD setup.sh /setup.sh
-RUN chmod +x /setup.sh
+ADD get-variable /get-variable
+RUN chmod +x setup.sh && chmod +x wait-for-it && chmod +x get-variable
 CMD ["/setup.sh"]

get-variable

@@ -0,0 +1,10 @@
+#!/usr/bin/env php
+<?php
+define("MEDIAWIKI", 1);
+define("HTML_ROOT", "/var/www/html");
+
+function wfLoadSkin() {}
+function wfLoadExtension() {}
+
+@include HTML_ROOT . "/LocalSettings.php";
+print_r($GLOBALS[$argv[1]]);

setup.sh

@@ -5,6 +5,8 @@ HTML_ROOT=/var/www/html
 # Run updater if we have an existing install
 if [[ -e "$HTML_ROOT/LocalSettings.php" ]]; then
     cd "$HTML_ROOT/maintenance"
+    DB_SERVER=$(/get-variable wgDBserver)
+    /wait-for-it "$DB_SERVER:3306"
     php update.php
 fi