Simple Docker Compose for MariaDB status unhealthy; but database seems fine

The Docker Compose healthcheck fails, but I can login to database just fine. What have I missed?

$ docker ps 
CONTAINER ID   IMAGE                   COMMAND                  CREATED         STATUS                     PORTS                                         NAMES
bc192ff6496f   mariadb:10.11.10-ubi9   "docker-entrypoint.s…"   4 minutes ago   Up 4 minutes (unhealthy)   0.0.0.0:4306->3306/tcp, [::]:4306->3306/tcp   spring-boot-db-1

The healthcheck command is:

$ mysql -u spring -P 4306 -pspring spring -Bse 'SELECT 1'
1

Logging in from command line:

$ mysql -u spring -P 4306 -pspring spring 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 4
Server version: 10.11.10-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [spring]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| spring             |
+--------------------+
2 rows in set (0.001 sec)

And compose.yml

services:
  db:
    image: mariadb:10.11.10-ubi9
    volumes:
      - mysqldata:/var/lib/mysql
    ports:
      - 4306:3306
    restart: unless-stopped
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_USER: spring
      MYSQL_PASSWORD: spring
      MYSQL_DATABASE: spring
    healthcheck:
      test: "mysql -u spring -P 4306 -pspring spring -Bse 'SELECT 1'"
      start_interval: 3s
      start_period: 15s
      interval: 2m
      retries: 3
      timeout: 5s

volumes:
  mysqldata:

Turns out the health check is done from inside the container, so I need to be using the internal port, not the mapped port, ie, 3306, nor 4306.

So the health check command should be

"mysql -u spring -P 3306 -pspring spring -Bse 'SELECT 1'"