Update React / Spring / MySQL example (#99)

* Update README.md title from NodeJS to Spring

Signed-off-by: Friedrich Greiner <greinerfriedrich@gmail.com>

* Always restart spring backend service

Signed-off-by: Friedrich Greiner <greinerfriedrich@gmail.com>

* Also pass db-password secret to spring backend

Signed-off-by: Friedrich Greiner <greinerfriedrich@gmail.com>

* Add healthcheck to the mysql service

 - a start_period of 30s + 15s (interval * retries) should be long enough for mysql to initialize

Signed-off-by: Friedrich Greiner <greinerfriedrich@gmail.com>

react-java-mysql/docker-compose.yaml

@@ -2,19 +2,28 @@ version: "3.7"
 services:
   backend:
     build: backend
+    restart: always
+    secrets:
+      - db-password
     environment:
       MYSQL_HOST: db
     networks:
       - react-spring
       - spring-mysql
     depends_on:
-      - db
+      db:
+        condition: service_healthy
   db:
     environment:
       MYSQL_DATABASE: example
       MYSQL_ROOT_PASSWORD_FILE: /run/secrets/db-password
     image: mysql:8.0.19
     restart: always
+    healthcheck:
+      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "--silent"]
+      interval: 3s
+      retries: 5
+      start_period: 30s
     secrets:
       - db-password
     volumes: