GitHub, Travis and status image

Since not so long ago GitHub provides an opportunity to build OpenSource projects on Travis CI. The integration is quite stunning and includes among other things:

• Single sign-on with GitHuub
• Automatic build setup with a single mouse click
• Status image generation

Well, I tried to setup build of my Spring examples today and Markdown gave ma a little bit of a hard time to figure out how to put together an image link to by build status. Finally I stumbled upon this stackoverflow.com question but the brackets were all wrong. Here's what it should look like:

[![_alt_text_](_image_url_)](_link_)

With the parentheses instead of brackets all works nice :)

And live is good again :)

Foreman and multiple ports per process

The problem

Composing an application of multiple software components is the de facto standard these days. It's rarely the case for the application to embed a database server, queue server or the like. To help manage the ever growing complexity of this kind of systems we can use Foreman - a Ruby application using a Procfile to spin off instances of declared services (same as for example Heroku uses to manage processes).

Many software components these days besides providing the core functionality tend to give the user some sort of administration interface. That interface is often available under different a port. Up until now Foreman assigned only one single port per process, via the $PORT environment variable. As I started using Foreman recently this inconvenience became a stopper for me trying to start ActiveMQ, 2 instances of MongoDB in a shard and Neo4j with my Sinatra application. All was nice but the lack of ability to start MongoDB's control interface on separate ports blew it all out of the water.

The solution

I've came to the conclusion that it'd be a really handy to use multiple ports not just for the case I just described. And so I created a ticket on GitHub for this. Being a forthcoming guy and all I decided to take a crack at implementing this functionality myself. A few hours later a working and tested solution covering all the cases was ready to be pulled in. Let's see if the maintainer will agree to pull it in :)

How to use it?

Assuming David will pull it in the formula is as follows:

alpha: command_to_start -p1 $PORT -p2 $PORT0
beta:  command_to_start -p1 $PORT1 -p3 $PORT9

What would that mean?

alpha would get assigned 2 ports: $PORT = 50xx and $PORT0 = 51xx
beta would get assigned 3 ports: $PORT = 52xx, $PORT1 = 53xx and $PORT9 = 54xx

Since Foreman makes an assumption that at most 100 ports are assigned to one variable this new functionality uses that to assign ranges for subsequent ports. And because I wanted to stay compatible with results not using this new feature the original port range numeration regardless of the usage of $PORT in the command stayed the same. That's why beta still gets the $PORT assigned even though it is not used.

Have a nice day!

AMQP, RabbitMQ and round robin

I'm working on a set of examples of how to use RabbitMQ from different languages. Among other things I've worked on reviewing the ruby AMQP gem examples. Unfortunately when it came to demonstrating multiple consumers (a sort of scalability example) I hit a snag: even though I have had 4 consumers only the first one was used.

After setting the number of test messages to a really high number things were finally looking up - the second and third and forth consumers were involved. But that sucked big time and to prove it I started digging further to find out what actually makes it do the things it does.

:prefetch => 1 was the setting (as stated on some stackoverflow.com page) but setting it alone didn't do the trick because that made the channel get only one message and that was it. To continue receiving messages they have had to be ack'ed.

Talking is cheap - here's the example code



Have fun!

The not so obvious fact about tag libraries

I've came across this thing today and quite frankly I feel a little bit ashamed that I didn't know it yet. The concept of tag libraries is not new in the JSP world. It's just unusual to write tags because one needs to provide a tag library description file along with it and that increases the complexity of the solution (or so it is seen).

The nice thing about tag libraries is that they don't necessarily need a TLD file to drive them - a folder is more than enough for simple cases:

File /WEB-INF/tags/hello.tag

Hello, world! from a tag

File /index.jsp

<@ taglib prefix="tags" tagdir="/WEB-INF/tags" %>

<tags:hello />

It's really that simple!

There's obviously more to it (how to pass the tag body, how to pass parameters to the tag) - maybe next time :)

GGTS 3.0 - first dissapointment

For the longest time I've tried and tried to use the navigation aids in STS (now GGTS) to move around between the controller and view. This feature is there in VS since forever and the buttons to do the same in STS have been around on the toolbar for a long time now. Unfortunately they don't do much..

You can torture them all you want but the navigation from within a controller action like

class HomeController {
    def index = {
        [ message: "Hello, world!" ]
    }

doesn't seem to bother those buttons much. Same for navigation from the view - or should I rather say it's the only "true teller in the bunch" as it stays inactive forever and for always...

I know, I know... I'm complaining again about new software and guys from SpringSource have done a tremendously good job and all that and I should stop yammering and congratulate them. But what should I do when the tooltip over the "T" icon says "Open the corresponding TagLib" and when I click on it while editing a controller it opens a "Create a new TagLib" wizard? Same thing with services and the "S" button. Guys, come on! Can't you at long last fix this disaster?

Anyways, I'll give it a try and let you know what I think about the functionality that actually works.

Gitorious in EC2

Previously I've written a lot about how tough it is to install Gitorious. By that time the script I provided was the only automated way of installing Gitorious (for free) on the Net. I needed that script to perform a test install of Gitorious and convince management that this software is the right way to go. Now that this goal has been achieved it's not maintained anymore - and it doesn't have to!

There's a new kid on the block from BitNami stable - the BitNami Gitorious stack.

I haven't seen it in action yet but it looks very promising:

• 3 installation options (native installer, VMware machine, Amazon EC2)
• the automated installer has all the dependencies
• It's based on a newer version of Gitorious - from May 2012

I'm downloading it now - will tell you more about the quality of this release soon. It it'll pan out I'm going to give it a try in Amazon EC2 to see how it performs over there.

Have a nice day!

Removing stuff from embedded arrays in MongoDB

How to remove items from embedded list "items" by regular expression /item/ ???

db.example.update(
  { _id: ObjectId("5024d352ef2ff4c4a103db5f") }, 
  { $pull: { items: { $regex: /item/ } } }
)

Do the same but on all documents in collection:

db.example.update({}, { $pull: { items: { $regex: /item/ } } }, false, true)

Oh I so wish it'd be in the official docs - I spent 2 days trying to figure it out!