Use direct link to mysql:5.7 image

docker-compose.yml

@@ -1,9 +1,7 @@
 version: '3'
 services:
   mysql_master:
-#    image: mysql:5.7
-    build:
-      context: ./master
+    image: mysql:5.7
     env_file:
       - ./master/mysql_master.env
     container_name: "mysql_master"

master/Dockerfile

@@ -1,5 +0,0 @@
-# see https://hub.docker.com/_/mysql/
-
-FROM mysql:5.7
-
-# RUN mysql -u root -e "GRANT REPLICATION SLAVE ON *.* TO 'mydb_slave_user'@'%' IDENTIFIED BY 'mydb_slave_pwd'; FLUSH PRIVILEGES;"