fix: MySQL health checks need to happen over TCP (#1207)

By using the correct health check (TCP, rather than UNIX socket) we can get
rid of the 10 second sleep.

See docker-library/mysql#930 for discussion of
health checks.

This commit also simplifies the wait-for-mysql code in the provisioning script.

Author: timmc-edx

Makefile

@@ -470,7 +470,6 @@ dev.dbcopyall8: ## Clean mysql80 container and copy data from old mysql 5.7 cont
 	docker volume rm devstack_mysql80_data
 	$(MAKE) dev.up.mysql57+mysql80
 	$(MAKE) dev.wait-for.mysql57+mysql80
-	sleep 10
 	docker compose exec -T mysql80 mysql -uroot mysql < provision-mysql80.sql
 	$(MAKE) $(_db_copy8_targets)
 	$(MAKE) stop

check.sh

@@ -56,8 +56,18 @@ run_check() {
 mysql_run_check() {
     container_name="$1"
     mysql_probe="SELECT EXISTS(SELECT 1 FROM mysql.user WHERE user = 'root')"
+    # The use of `--protocol tcp` forces MySQL to connect over TCP rather than
+    # via a UNIX socket. This is needed because when MySQL starts for the first
+    # time in a new container, it starts a "temporary server" that runs for a
+    # few seconds and then shuts down before the "real" server starts up. The
+    # temporary server does not listen on the TCP port, but if the mysql
+    # command is not told which server to use, it will first try the UNIX
+    # socket and only after that will it try the default TCP port.
+    #
+    # By specifying that mysql should use TCP, we won't get an early false
+    # positive "ready" response while the temporary server is running.
     run_check "${container_name}_query" "$container_name" \
-        "docker compose exec -T $(printf %q "$container_name") mysql -uroot -se $(printf %q "$mysql_probe")"
+        "docker compose exec -T $(printf %q "$container_name") mysql --protocol tcp -uroot -se $(printf %q "$mysql_probe")"
 }
 
 if should_check mysql57; then

provision.sh

@@ -128,25 +128,10 @@ if needs_mongo "$to_provision_ordered"; then
 	docker compose up -d mongo
 fi
 
-# Ensure the MySQL5 server is online and usable
-echo "${GREEN}Waiting for MySQL 5.7.${NC}"
-make dev.wait-for.mysql57
-
-# Ensure the MySQL8 server is online and usable
-echo "${GREEN}Waiting for MySQL 8.0.${NC}"
-make dev.wait-for.mysql80
-
-# In the event of a fresh MySQL container, wait a few seconds for the server to restart
-# See https://github.com/docker-library/mysql/issues/245 for why this is necessary.
-sleep 10
-
-echo "${GREEN}Waiting for MySQL 5.7 to restart.${NC}"
-make dev.wait-for.mysql57
-echo -e "${GREEN}MySQL5 ready.${NC}"
-
-echo "${GREEN}Waiting for MySQL 8.0 to restart.${NC}"
-make dev.wait-for.mysql80
-echo -e "${GREEN}MySQL8 ready.${NC}"
+# Ensure the MySQL server is online and usable
+echo -e "${GREEN}Waiting for MySQL.${NC}"
+make dev.wait-for.mysql57+mysql80
+echo -e "${GREEN}MySQL is ready.${NC}"
 
 # Ensure that the MySQL databases and users are created for all IDAs.
 # (A no-op for databases and users that already exist).