How to handle a 'Configuration error[Cannot connect to database [...]]' - scala

Question

I am implementing a web service with the Play Framework, that uses multiple databases. All databases are configured in the conf/application.conf by specifying the db.database1..., db.database2... properties.
At startup, play will try to establish connections to all databases configured in the database and if one connection fails, the service will not start.
In my case, not all databases are necessary to start the web service, but the web service can still run with limited functionality, if some databases are not available. Since not all databases are under my control, it is crucial for my web service to handle a connection error.
Therefore my question:
Is there a way to either
handle the connection error by overriding some 'onError' method or insert a try-catch at the right place or
manually create the Datasources at runtime to handle the error when they are created
I would prefer solution 2.
I am using play version 2.4.2 with scala version 2.11.7.
Since the whole exceptions fills multiple pages, I only insert the first lines here:
CreationException: Unable to create injector, see the following errors:
1) Error in custom provider, Configuration error: Configuration error[Cannot connect to database [foo]]
while locating play.api.db.DBApiProvider
while locating play.api.db.DBApi
for field at play.api.db.NamedDatabaseProvider.dbApi(DBModule.scala:80)
while locating play.api.db.NamedDatabaseProvider
at com.google.inject.util.Providers$GuicifiedProviderWithDependencies.initialize(Providers.java:149)
at play.api.db.DBModule$$anonfun$namedDatabaseBindings$1.apply(DBModule.scala:34):
Binding(interface play.api.db.Database qualified with QualifierInstance(#play.db.NamedDatabase(value=appstate)) to ProviderTarget(play.api.db.NamedDatabaseProvider#1a7884c6)) (via modules: com.google.inject.util.Modules$OverrideModule -> play.api.inject.guice.GuiceableModuleConversions$$anon$1)
Caused by: Configuration error: Configuration error[Cannot connect to database [foo]]
at play.api.Configuration$.configError(Configuration.scala:178)
at play.api.Configuration.reportError(Configuration.scala:829)
at play.api.db.DefaultDBApi$$anonfun$connect$1.apply(DefaultDBApi.scala:48)
at play.api.db.DefaultDBApi$$anonfun$connect$1.apply(DefaultDBApi.scala:42)
at scala.collection.immutable.List.foreach(List.scala:381)
at play.api.db.DefaultDBApi.connect(DefaultDBApi.scala:42)
at play.api.db.DBApiProvider.get$lzycompute(DBModule.scala:72)

Answer 1

I remember that exists a Global Settings configuration file to catch errors when the application starts.
Take a look here: https://www.playframework.com/documentation/2.0/ScalaGlobal I know you are using a more recent play version but you will get a more general idea how it works.
In play 2.4.x this file was removed and uses DI now (https://www.playframework.com/documentation/2.4.x/GlobalSettings).

Answer 2

To solve my problem, I ended up writing my own wrapper for BoneCP. This way the initialization of the ConnectionPools were in my hands and I could handle connection errors.
Instead of using the db prefix, I use the prefix database (so that Play will not automatically parse its content) in a new config file database.conf.
object ConnectionPool {
private var connectionPools = Map.empty[String, BoneCP]
val config = ConfigFactory.parseFile(new File("conf/database.conf"))
private def dbConfig(dbId: String): ConfigObject = {
config.getObject("database." + dbId).asInstanceOf[ConfigObject]
}
def createConnectionPool(dbId: String): BoneCP = {
val dbConf = dbConfig(dbId)
val cpConfig: BoneCPConfig = new BoneCPConfig()
cpConfig.setJdbcUrl(dbConf.get("url").unwrapped().toString)
cpConfig.setUsername(dbConf.get("user").unwrapped().toString)
cpConfig.setPassword(dbConf.get("password").unwrapped().toString)
new BoneCP(cpConfig)
}
def getConnectionPool(dbId: String): BoneCP = {
if(!connectionPools.contains(dbId)) {
val cp = createConnectionPool(dbId)
connectionPools = (connectionPools + (dbId -> cp))
}
connectionPools(dbId)
}
def getConnection(dbId: String): Connection = {
getConnectionPool(dbId).getConnection()
}
def withConnection[T](dbId: String)(fun: Connection => T): T = {
val conn = getConnection(dbId)
val t = fun(conn)
conn.close()
t
}
}