Cannot connect to MySQL in Docker from .NET app (in docker)

Question

I have a docker stack with a .NET app and a MySQL server.

  mysql:
    image: mysql
    ports: 
      - 3306:3306
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: "Password@1234"
      MYSQL_DATABASE: "db"
  mongo:
    image: mongo
    restart: always
    environment:
      MONGO_INITDB_ROOT_USERNAME: "root"
      MONGO_INITDB_ROOT_PASSWORD: "Password@1234"
    ports:
      - 27017:27017
  app:
    image: ${DOCKER_REGISTRY-}app
    build:
      context: .
      dockerfile: ../App/Dockerfile
    ports:
      - 7040:443
    environment:
      - ASPNETCORE_URLS=https://+:443;
    depends_on:
        - mysql
        - mongo

When I try to connect to the server with the following connection string:

"Server=mysql;User=root;Pwd=Password@1234;Database=db"

I get an exception like so:

System.InvalidOperationException: An exception has been raised that is likely due to a transient failure. Consider enabling transient error resiliency by adding 'EnableRetryOnFailure()' to the UseMySq' call.
Inner Exception: MySqlException: Unable to connect to any of the specified MySQL hosts.

Quite weird since I can connect to the database from Azure Data Studio.

Can't figure out what's wrong here. Not sure how this is transient, since when I use DbContext.Database.CanConnect() it returns false.

Tried using different users in yaml, different values of the con string, adding SSL. Nothing worked.

Answer 1

Very stupid reason for the issue.

When using

options.UseMySql(ServerVersion.AutoDetect(conString))

I didn't add the con string as the first property. Now it works with this:

options.UseMySql(conString, ServerVersion.AutoDetect(conString))

I thought since

public static DbContextOptionsBuilder UseMySql([NotNull] this DbContextOptionsBuilder optionsBuilder, [CanBeNull] string connectionString, [NotNull] ServerVersion serverVersion, [CanBeNull] Action<MySqlDbContextOptionsBuilder> mySqlOptionsAction = null)

says that the ConString can be null it will somehow understand what the con string is but it was a baseless asumption.