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Relay JDBC - Access JDBC data sources through an intermediate proxy server

Overview

Relay JDBC is a custom JDBC driver implementation that allows a target database to be accessed through various network transports different from that supported by the JDBC driver of the target database.

Instead of connecting to the database directly, using the JDBC driver of the target database, a client application uses the Relay JDBC driver to connect to the Relay JDBC server, which internally connects to the target database using the JDBC driver of the target database and relays all communication between the client application and the target database.

Both the client JDBC driver and the relay server are packaged into one JAR file allowing a very quick setup.

+--------------------+
| Client Application |
+--------------------+
          |      
+--------------------+
| Relay JDBC driver  |
+--------------------+
          |      
          |      
          |      
+--------------------+
| Relay JDBC Server  |
+--------------------+
          |      
+------------------------------+
| Target Database JDBC driver  |
+------------------------------+
          |      
+------------------------------+
|  Target Database Server      |
+------------------------------+

Running the server

Start the JAR file from command line and specify transport and its configuration.

  1. Create a configuration file similar to the following and save it to relayjdbc-config.xml in the current working directory
<relayjdbc-configuration>
	<connection
		id="h2db"
		driver="org.h2.Driver"
		url="jdbc:h2:mem:test"
		user="sa"
       	password="">
    	<connection-pool
                   maxActive="4"
                   maxIdle="1"
                   maxWait="10000"
                   timeBetweenEvictionRunsMillis="5000"
                   minEvictableIdleTimeMillis="10000"/>
	</connection>
</relayjdbc-configuration>

  1. Start the JAR file as a single JAR application, specifying the transport used and its configuration. For example, the following will start the HTTP transport with HTTP listening on port 8080 and HTTPS on port 8443: java -jar relay-jdbc-*.jar http 8080

  2. Add the RelayJDBC JAR and the actual delegate driver JARs to the client application and use RelayJDBC connection URL to connect to the relay. For example: jdbc:relayjdbc:http://localhost:8080#h2db

NOTE: if there are more than one connections defined in the connection file, the URL should reference the id attribute of the connection (here, in the sample: id="h2db") at the end of the connection URL (here, in the sample URL: ...#h2db).

Transports and their configuration

HTTP Transport

This transport starts an embedded Servlet container that will listen to incoming HTTP requests.

Starting the relay server

Start command: http <http port>

  • Command line argument: http
  • Configuration arguments
    • http port: the port to listen on for incoming HTTP requests (required)
    • https port: the port to listen on for incoming HTTPs requests (optional)

Examples:

  1. java -jar relay-jdbc-*.jar http 8080 This will start the HTTP transport with HTTP listening on port 8080 and NO HTTP listener

JDBC URL to connect with

For the HTTP transport, the following URL format is to be used: jdbc:relayjdbc:http://<host name>:<port number>#<connection ID>

Where the placeholders are:

  • host name: the host to connect to (required)
  • port number: the port to connect to (required)
  • connection ID: the value of the ID attribute of the connection tag (optional)

Sample URL: jdbc:relayjdbc:http://localhost:8080#h2db

Limitations of HTTP Transport

At the moment, HTTP transport does not have any authentication or encryption built-in. The Relay JDBC Server will simply pass authentication to the database server. You will have to ensure that only authorized users can connect to the service by implementing firewall settings.

BASE64PIPE / SSHPIPE Transport

BASE64PIPE transport starts a listener, that awaits incoming messages from the standard input and responds to the standard output. All protocol messages are Base64 encoded, allowing this transport to be used through text-only piping mechanisms.

CAUTION: this transport is NOT an SSH tunnel! Unlike an SSH tunnel, this transport works solely via transmitting connection payload data through the established SSH session and does not open a forwarded port. The remote server is started as a sub-process of the remote SSH shell session.

While theoretically, a number of client transports could use this connection type, in practice, only the sshpipe client connection type is used: that is, the Relay JDBC driver establishes a SSH connection to a remote system, starts a Relay JDBC Server with BASE64PIPE transport then connects to the server through standard I/O pipes.

Starting the relay server

Start command: base64pipe <configuration file> [properties file]

  • Command line argument: base64pipe
  • Configuration arguments
    • configuration file: the RelayJDBC configuration file (required)
    • properties file: the RelayJDBC properties file (optional)

Examples:

  1. java -jar relay-jdbc-*.jar base64pipe config.xml This will start the BASE64PIPE transport using the config.xml configuration file

  2. java -jar relay-jdbc-*.jar base64pipe config.xml settings.properties This will start the BASE64PIPE transport using the config.xml configuration file and settings.properties file

JDBC URL to connect with

For the BASE64PIPE transport, the following URL format is to be used: jdbc:relayjdbc:sshpipe://<host name>:<port number>

Where the placeholders are: * host name: the host to connect to (required)
* port number: the port to connect to (required)

Sample URL: jdbc:relayjdbc:sshpipe://localhost:2222

Mandatory properties to be passed

The following properties must be passed to the connection establish call (e.g. java.sql.DriverManager.getConnection(java.lang.String, java.util.Properties)) when using this connection type:

  • ssh.username: the username for the SSH authentication
  • ssh.password: the password for the SSH authentication
  • ssh.remoteCommand: the remote command to execute, which will start the BASE64PIPE transport server

NOTE: ssh.remoteCommand is the actual OS command that starts the Relay JDBC Server on the remote machine. You probably want create a shell script to perform these steps. Remember: if you use this transport mechanism, you will have to disable logging to the console as that would conflict with the messages emitted to the standard output pipe. (Otherwise the client will attempt -- and fail to -- un-marshall the console log messages emitted by the remote server)

Optional properties to be passed

The following properties can be passed to the connection establish call (e.g. java.sql.DriverManager.getConnection(java.lang.String, java.util.Properties)) when using this connection type:

  • ssh.strictHostKeyChecking: enforce strict host key matching: yes/no - default is no

Limitations of BASE64PIPE / SSHPIPE Transport

Special log configuration requirement for BASE64PIPE

IMPORTANT NOTICE: Transport BASE64PIPE works by piping protocol message data through the standard input/output. If BASE64PIPE is used, console logging has to be disabled (e.g. redirect all logs to a file)

Single connection configuration per file

Unlike other transports, BASE64PIPE / SSHPIPE Transport does not support having multiple connection configurations in one configuration file. You have to use the the default connection type and cannot specify a connection Id in the Relay JDBC driver JDBC URL.

Log configuration

RelayJDBC uses log4j for logging and expects a log4j configuration file to be present in the current working directory called either relay-jdbc.log4j.xml (XML format) or relay-jdbc.log4j.properties (properties format).

Sample relay-jdbc.log4j.properties

# Root logger option
log4j.rootLogger=WARN, file

# Direct log messages to a log file
log4j.appender.file=org.apache.log4j.RollingFileAppender

log4j.appender.file.File=relay-jdbc.log
log4j.appender.file.MaxFileSize=2MB
log4j.appender.file.MaxBackupIndex=2
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

IMPORTANT NOTICE: Transport BASE64PIPE works by piping protocol message data through the standard input/output. If BASE64PIPE is used, console logging have to be disabled (e.g. redirect all logs to a file)

Download

Relay JDBC is available in Maven Central.

Maven Central