In my environment, there are OS environment variables called OPENSHIFT_DB_HOST and OPENSHIFT_DB_PORT. These variables can be used to build the address pointing to a MySQL server. Both variables have sensible values (e.g. OPENSHIFT_DB_HOST = 127.0.0.1 .... OPENSHIFT_DB_PORT = 3306 ) In a logback XML configuration file, I'm configuring a DBAppender. I'm using logback's variable substitution in the following line. <url>jdbc:mysql://${OPENSHIFT_DB_HOST}:${OPENSHIFT_DB_PORT}/mydb?useUnicode=true&characterEncoding=UTF-8</url> As you can see, I'm using both OS environment variables to build the address, separated by a colon (":"). The resulting URL should therefore look like "jdbc:mysql://127.0.0.1:3306/mydb?useUnicode=true&characterEncoding=UTF-8" When logback parses my logback XML configuration file, I get the following exception: ~~~Begin: Exception stack trace~~~ 18:44:06,288 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - About to instantiate appender of type [ch.qos.logback.classic.db.DBAppender] 18:44:06,299 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - Naming appender as [db] 18:44:07,180 |-WARN in ch.qos.logback.core.db.DataSourceConnectionSource@12c662b - Could not get a connection to discover the dialect to use. com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Cannot load connection class because of underlying exceptio n: 'java.lang.NumberFormatException: For input string: "${OPENSHIFT_DB_PORT}"'. at com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Cannot load connection class because of underlying exception: 'java.lang.NumberFormatException: For input string: "${OPENSHIFT_DB_PORT}"'. at at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) at at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at at java.lang.reflect.Constructor.newInstance(Constructor.java:525) at at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) at at com.mysql.jdbc.Util.getInstance(Util.java:386) at at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1014) at at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:988) at at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:974) at at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:919) at at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:343) at at com.mysql.jdbc.jdbc2.optional.MysqlDataSource.getConnection(MysqlDataSource.java:443) at at com.mysql.jdbc.jdbc2.optional.MysqlDataSource.getConnection(MysqlDataSource.java:141) at at com.mysql.jdbc.jdbc2.optional.MysqlDataSource.getConnection(MysqlDataSource.java:111) at at ch.qos.logback.core.db.DataSourceConnectionSource.getConnection(DataSourceConnectionSource.java:72) at at ch.qos.logback.core.db.DataSourceConnectionSource.start(DataSourceConnectionSource.java:46) at at ch.qos.logback.core.joran.action.NestedComplexPropertyIA.end(NestedComplexPropertyIA.java:167) at at ch.qos.logback.core.joran.spi.Interpreter.callEndAction(Interpreter.java:318) at at ch.qos.logback.core.joran.spi.Interpreter.endElement(Interpreter.java:197) at at ch.qos.logback.core.joran.spi.Interpreter.endElement(Interpreter.java:183) at at ch.qos.logback.core.joran.spi.EventPlayer.play(EventPlayer.java:62) at at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:157) at at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:143) at at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:106) at at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:56) at at ch.qos.logback.classic.util.ContextInitializer.configureByResource(ContextInitializer.java:75) at at ch.qos.logback.classic.util.ContextInitializer.autoConfig(ContextInitializer.java:148) at at org.slf4j.impl.StaticLoggerBinder.init(StaticLoggerBinder.java:84) at at org.slf4j.impl.StaticLoggerBinder.<clinit>(StaticLoggerBinder.java:54) at at org.slf4j.LoggerFactory.bind(LoggerFactory.java:128) at at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:107) at at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:295) at at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:269) at at org.eclipse.jetty.util.log.Slf4jLog.<init>(Slf4jLog.java:38) at at org.eclipse.jetty.util.log.Slf4jLog.<init>(Slf4jLog.java:32) at at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) at at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at at java.lang.reflect.Constructor.newInstance(Constructor.java:525) at at java.lang.Class.newInstance0(Class.java:372) at at java.lang.Class.newInstance(Class.java:325) at at org.eclipse.jetty.util.log.Log.initialized(Log.java:161) at at org.eclipse.jetty.util.log.Log.getLogger(Log.java:435) at at org.eclipse.jetty.util.log.Log.getLogger(Log.java:425) at at org.eclipse.jetty.xml.XmlConfiguration.<clinit>(XmlConfiguration.java:72) at at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at at java.lang.reflect.Method.invoke(Method.java:601) at at org.eclipse.jetty.start.Main.invokeMain(Main.java:468) at at org.eclipse.jetty.start.Main.start(Main.java:616) at at org.eclipse.jetty.start.Main.main(Main.java:92) Caused by: java.lang.NumberFormatException: For input string: "${OPENSHIFT_DB_PORT}" at at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at at java.lang.Integer.parseInt(Integer.java:481) at at java.lang.Integer.parseInt(Integer.java:527) at at com.mysql.jdbc.NonRegisteringDriver.port(NonRegisteringDriver.java:866) at at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:334) at ... 41 common frames omitted ~~~End: Exception stack trace~~~ As you can see, logback seems to have not substituted the second variable called ${OPENSHIFT_DB_PORT}, and instead took the raw string "${OPENSHIFT_DB_PORT}" to pass it to the underlying URL parser. Can it be that * logback has problems substituting two (and more?) variables in a single expression? * logback has problems when two variables are separated by a colon? Cheers