一开始用的mysql 8.0镜像，出现error establishing a database connection.
后面换成mysql:5.7
命令如下：
docker service create --name mysql --env MYSQL_DB_PASSWORD=root --env MYSQL_DATABASE=wordpress --mount type=volume,source=mysql-data,destination=/var/lib/mysql --network demo mysql:5.7

然后一直出现Detected task failure 。

通过 docker service logs -f mysql:
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01 11:24:04+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 5.7.28-1debian9 started.
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01 11:24:04+00:00 [Note] [Entrypoint]: Switching to dedicated user 'mysql’
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01 11:24:04+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 5.7.28-1debian9 started.
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.548549Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.550061Z 0 [Note] mysqld (mysqld 5.7.28) starting as process 1 …
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.552951Z 0 [Note] InnoDB: PUNCH HOLE support available
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.553030Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.553040Z 0 [Note] InnoDB: Uses event mutexes
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.553044Z 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.553047Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.11
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.553050Z 0 [Note] InnoDB: Using Linux native AIO
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.553290Z 0 [Note] InnoDB: Number of pools: 1
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.553396Z 0 [Note] InnoDB: Using CPU crc32 instructions
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.555395Z 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.562620Z 0 [Note] InnoDB: Completed initialization of buffer pool
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.565457Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01T11:24:04.577842Z 0 [ERROR] [FATAL] InnoDB: Table flags are 0 in the data dictionary but the flags in file ./ibdata1 are 0x4800!
mysql.1.p117gjv9o9rk@swarm-manager | 2020-01-01 11:24:04 0x7f4bca560740 InnoDB: Assertion failure in thread 139963493910336 in file ut0ut.cc line 918