Test database connection during app startup

[Ghurtchu]

Hi, @daniel-ciocirlan!

Currently we don't test the connection to database during the app startup. Could we add a simple logging in Application.scala, like this?

import doobie.implicits.*

  val appResource = for { 
    xa <- Database.makePostgresResource[IO](postgresConfig)
    _  <- sql"select 0"
          .query[Int]
          .unique
          .transact(xa)
          .flatTap(_ => logger.info("Managed to establish connection to database"))
          .onError(e => logger.error(e.getMessage))
          .toResource
    _ <- ...
  } yield ...
}

I discovered this when I realized that postgres-config.url in my application.conf was wrong.

I was getting this in the output:

Caused by: java.net.ConnectException: Connection refused
        at java.base/sun.nio.ch.Net.pollConnect(Native Method)
        at java.base/sun.nio.ch.Net.pollConnectNow(Net.java:672)
        at java.base/sun.nio.ch.NioSocketImpl.timedFinishConnect(NioSocketImpl.java:554)
        at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:602)
        at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:327)
        at java.base/java.net.Socket.connect(Socket.java:633)
        at org.postgresql.core.PGStream.createSocket(PGStream.java:231)
        at org.postgresql.core.PGStream.<init>(PGStream.java:95)
        at org.postgresql.core.v3.ConnectionFactoryImpl.tryConnect(ConnectionFactoryImpl.java:98)
        at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:213)
        ... 18 more