Wednesday, May 07, 2014

RHQ 4.11 released

I am proud to announce the immediate availability of RHQ 4.11.

As always this release contains new features and bug fixes.

Notable changes are:

  • Plugins can now define plugin specific DynaGroup expressions, which can even be auto-activated
  • Further agent footprint reduction for jmx-clients (especially if the agent runs on jdk 1.6)
  • Much improved agent install via ssh from the RHQ UI.
  • Support for Oracle 12 as backend database
  • New login screen that follows

As always RHQ is available for download in form of a zip archive. If you want to try out RHQ without too much setup, you can also use a pre-created Docker image
from (the link contains setup information).

Please consult the release notes for further details and a download link.

If you only want to have a quick look, you can also consult a
running RHQ 4.11 instance that we have set up. User/Pass are guest / rhqguest

Special thanks goes to

  • Elias Ross
  • Michael Burman

for their code contributions for this release.

My first Netty-based server

Netty logo
RHQ logo

For our rhq-metrics project (and actually for RHQ proper) I wanted to be able to receive syslog messages, parse them and in case of content in the form of

type=metric thread.count=11 heap.permgen.size=20040000

forward the individual key-value pairs (e.g. thread.count=11) to a rest endpoint for further processing.

After I started with the usual plain Java ServerSocket.. code I realized that this may become cumbersome and that this would be the perfect opportunity to check out Netty. Luckily I already had an Early Access copy of Netty in Action lying around and was ready to start.

Writing the first server that listens on TCP port 5140 to receive messages was easy and modifying /etc/syslog.conf to forward messages to that port as well.

Unfortunately I did not get any message.

I turned out that on OS/X syslog message forwarding is only UDP. So I sat down, converted the code to use UDP and was sort of happy. I was also able to create the backend connection to the REST server, but here I was missing the piece on how to "forward" the incoming data to the rest-client connection.

Luckily my colleague Norman Maurer, one of the Netty gurus helped me a lot and so I got that going.

After this worked, I continued and added a TCP server too, so that it is now possible to receive messages over TCP and UDP.

The (current) final setup looks like this:

Overviw of my Netty app

I need two different decoders here, as for TCP the (payload) data received is directly contained in a ByteBuf while for UDP it is inside a DatagramPacker and needs to be pulled out into a ByteBuf for further decoding.

One larger issue I had during development (aside from wrapping my head around "The Netty Way" of doing things) was that I wrote a Decoder like

public class UdpSyslogEventDecoder extends

protected void decode(ChannelHandlerContext ctx, DatagramPacket msg, List<Object> out) throws Exception {

and it never got called by Netty. I could see that it was instantiated when the pipeline was set up, but for incoming messages it was just bypassed.

After I added a method

public boolean acceptInboundMessage(Object msg) throws Exception {
return true;

my decoder was called, but Netty was throwing ClassCastExceptions, but they were pretty helpful, as it turned out that the IDE automatically imported, which is not what Netty wants here. As Netty checks for the signature of the decode() and this did not match, Netty just ignored the decoder.

You can find the source of this server on GitHub.