If you face this error on your local then you need to change your DB configuration to run the project on local with docker.
Your docker config file might look like
version: '2' services: web: build: ./docker/php ports: - 80:80 volumes: - .:/var/www/html/ links: - db db: build: ./docker/mysql ports: - 3306
In above settings (db:) this is your localhost so your database configuration will look like
database host: db
database username: root
database password : 12345
In short, you need to replace “localhost” with “db” and it’s done.