Wait for MySQL to be reading before initialising/upgrading database

docker/PowerDNS-Admin/Dockerfile

@@ -22,6 +22,9 @@ RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" > /etc/apt/sources.lis
 RUN apt-get update -y
 RUN apt-get install -y yarn
 
+# Install Netcat for DB healthcheck
+RUN apt-get install -y netcat
+
 # lib for building mysql db driver
 RUN apt-get install -y libmysqlclient-dev
 

docker/PowerDNS-Admin/entrypoint.sh

@@ -1,5 +1,14 @@
 #!/bin/sh
 
+# Wait for us to be able to connect to MySQL before proceeding
+until nc -zv \
+  $PDA_DB_HOST \
+  3306;
+do
+  echo "MySQL ($PDA_DB_HOST) is unavailable - sleeping"
+  sleep 1
+done
+
 cd /powerdns-admin
 
 if [ ! -d "/powerdns-admin/migrations" ]; then