Deploying fresh docker-compose fails on backdrop because mysql isn't ready

[tabroughton]

Mysql db is starting up and so is backdrop container. When backdrop uses a cache for the composer install then it's too fast for mysql and the installation of backdrop fails on drush si because the db isn't ready for connections.

The current way to manage this is to composer install and pull packages, the time it takes allows for mysql to become ready. This is purely chance, takes longer to create containers than it should and uses much more bandwidth than is necessary.

[tabroughton]

suggestions https://docs.docker.com/compose/startup-order/

[tabroughton]

using https://github.com/vishnubob/wait-for-it