Implementing keep-alive messages in Netty using WriteTimeoutHandler

I would suggest to add the IdleStateHandler and then add your custom implementation of IdleStateAwareUpstreamHandler which can react on the idle state. This works out very well for me on many different projects.

The javadocs list the following example, that you could use as the base of your implementation:

public class MyPipelineFactory implements ChannelPipelineFactory {

    private final Timer timer;
    private final ChannelHandler idleStateHandler;

    public MyPipelineFactory(Timer timer) {
        this.timer = timer;
        this.idleStateHandler = new IdleStateHandler(timer, 60, 30, 0);
        // timer must be shared.
    }

    public ChannelPipeline getPipeline() {
        return Channels.pipeline(
            idleStateHandler,
            new MyHandler());
    }
}

// Handler should handle the IdleStateEvent triggered by IdleStateHandler.
public class MyHandler extends IdleStateAwareChannelHandler {

    @Override
    public void channelIdle(ChannelHandlerContext ctx, IdleStateEvent e) {
        if (e.getState() == IdleState.READER_IDLE) {
            e.getChannel().close();
        } else if (e.getState() == IdleState.WRITER_IDLE) {
            e.getChannel().write(new PingMessage());
        }
    }
}

ServerBootstrap bootstrap = ...;
Timer timer = new HashedWheelTimer();
...
bootstrap.setPipelineFactory(new MyPipelineFactory(timer));
...

For Netty 4.0 and newer, you should extend ChannelDuplexHandler like in example from IdleStateHandler documentation :

 // An example that sends a ping message when there is no outbound traffic
 // for 30 seconds.  The connection is closed when there is no inbound traffic
 // for 60 seconds.

 public class MyChannelInitializer extends ChannelInitializer<Channel> {
     @Override
     public void initChannel(Channel channel) {
         channel.pipeline().addLast("idleStateHandler", new IdleStateHandler(60, 30, 0));
         channel.pipeline().addLast("myHandler", new MyHandler());
     }
 }

 // Handler should handle the IdleStateEvent triggered by IdleStateHandler.
 public class MyHandler extends ChannelDuplexHandler {
     @Override
     public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
         if (evt instanceof IdleStateEvent) {
             IdleStateEvent e = (IdleStateEvent) evt;
             if (e.state() == IdleState.READER_IDLE) {
                 ctx.close();
             } else if (e.state() == IdleState.WRITER_IDLE) {
                 ctx.writeAndFlush(new PingMessage());
             }
         }
     }
 }