Coder's Desiderata

Out of Phase: Global Game Jam 2015

This is the first post in a series that will reflect on the project from various stages, covering pros and cons of the creative process and implementation of the game. This review is a long time coming, it was originally started right after the 2015 Global Game Jam.

In January I broke a lull by participating in the annual 48 hour Global Game Jam. Prior to this jam, it had been some time since prototyping a game of my own. Game jams in general are a great opportunity to break creators block and start fresh.

I started a project called Out of Phase. The original idea was to create a two player game that involved a series of puzzles contained within chambers, similar to Portal 2. There was a twist, where the environment was slightly different between the two players, requiring them to communicate between each other to solve the puzzles.

At the end of the 48 hour jam, I produced the first version. While not complete, it still gave an example of the general concept with a couple puzzle examples. Two players were supported through a local co-op mode, where chracters were toggled by hitting the tab key.

For this post, I’ll give a general overview of the tools and design ideas that took place at the Global Game Jam.

Framework

It’s a good rule of thumb in game jams not to build your own framework. Your focus is on producing a game, not a toolset. Phaser.io is a real snazzy HTML5 game engine/framework. It comes with a tilemap loader, collision detection, WebGL support, and a plethora of other goodies to make life easier.

Another guideline with jams is to know your toolset so that you’re not wasting time figuring out how to use the tools. I only had a little experience with Phaser.io prior to the jam, so I didn’t follow this one completely. However being very experienced with JavaScript and the concepts that Phaser.io is built on, I was able to get started very quickly and iterate through ideas easily.

One problem I ran into early on was selecting the wrong physics engine for collision detection. This set me back a little, but helped me learn the differences between the P2 and Arcade systems. In Phaser.io, you can actually have more than one system active, so they’re not exclusive to each other.

Continue Reading »

Keep your server running with monitoring services

In a world of 99.999% up time, keeping a service running is a big deal. How do you compete? That is where monitoring and automated server management comes into play.

It is a good idea to use both a local and remote monitoring solutions, with the remote service being a fail-safe that will send out a notification when a website or service  is unreachable or has poor latency.

With remote monitoring, there are many options that will scale to different needs. For example, I use 24×7 by Zoho for basic port monitoring. This service will send a notification if an app is no longer reachable from the internet. There are many monitoring services out there, so it would be worthwhile to search around and compare.

The next step is something that runs locally, has more granular monitoring, and will take actions to resolve a problem when it is detected. Monnit will do just this. It is a daemon that runs on the server and monitors resources and processes. It has the ability to restart programs and send notifications under specific conditions, such as when memory or CPU consumption exceeds a given threshold, and low disk space. It can also detect a continually failing applications by tracking the PID.

Here are some configuration examples of monnit for Apache, MySQL, and SOLR. Comments have been added to describe what they do. Each example uses an alert directive, which requires a recipient to be configured. This is done by setting the following in the config file:

set alert example@email.com

APACHE

## Custom Apache2 setup
check process apache2 with pidfile /var/run/apache2.pid
group www
start program = "/etc/init.d/apache2 start"
stop program = "/etc/init.d/apache2 stop"

# Send alert if Apache isn't listening to specified port
if failed host localhost port 80 then alert

# Restart daemon if children processes > 250
if children > 250 then restart

# Alert if load avg stays high with given criteria
if loadavg(5min) greater than 80 for 8 cycles then alert

# Stop trying to restart daemon if restarts aren't working
if 3 restarts within 5 cycles then timeout

MySQL

## Custom MySQLD setup
check process mysqld with pidfile /var/run/mysqld/mysqld.pid
group root
start program = "/etc/init.d/mysql start"
stop program = "/etc/init.d/mysql stop"

# Send alert if MYSQLD isn't listening to specified port
if failed host localhost port 3306 then alert

SOLR

## SOLR Check
check process solr with pidfile /var/run/solr.pid
group root
start program = "/etc/init.d/solr start"
stop program = "/etc/init.d/solr stop"

# Send alert if SOLR isn't listening to specified port
if failed host localhost port 8983 then alert

# Restart daemon if SOLR isn't listening to specified port
if failed host localhost port 8983 then restart

# Stop trying to restart if restarts aren't working
if 5 restart within 5 cycles then timeout

In each of these, Monnit has at least a check that the app is listening on a designated port. If it is not, a restart of the service is attempted. With Apache, if it is running too many children, the service will be restarted to fix this. (Note: Apache does have a setting in Apache conf that set max children threads that should help avoid triggering the children processes check) In some cases the service will be shutdown if it is running hot for too long.

Conclusion

Keeping a daemon running and gathering information about it before something goes wrong is crucial in maintaining a quality application or service. Monitoring tools like 24×7 and Monnit make this easier and are a must on any IT toolbelt.

Manage Your Daemons With Upstarts

I am finding the need for custom Linux service scripts more and more. This is in the case where a program I want to run in the background does not already have one for one reason or another. Maybe I’m compiling instead of using apt, or sometimes I am creating my own app.

In the past I’ve used the traditional init script format that exists in /etc/init.d. This proved to be tedious. Unless I already had the init script on hand, I would need to code it out in bash script, like so:

#!/bin/bash
#
# Debug SMTP Service
#
case "$1" in
start)
if [ -f "/var/run/debugsmtp.pid" ]
then
    echo "Service already running"
else
    echo "Starting service..."
    python -m smtpd -n -c DebuggingServer localhost:25 &
    echo "$!" > /var/run/debugsmtp.pid
    echo "Service started"
fi
;;
stop)
if [ -f "/var/run/debugsmtp.pid" ]
then
    PID=`cat /var/run/debugsmtp.pid`
    kill -9 "$PID"
    rm /var/run/debugsmtp.pid

if [ ! -f "/var/run/debugsmtp.pid" ]
then
    echo "Service stopped"
fi
else
    echo "Service not running"
fi
;;
*)
echo "Service"
echo $"Usage: $0 {start|stop|status}"
exit 1
esac
exit 0

As you can see, there are sections to handle different commands, in this case it is just start and stop. With other programs there may also be restart, status and reload.

Start checks if the process is already running by checking if a PID file exists. If it does, then the service is assumed to already be running. If not, the script goes on to start the process and stuffs the process ID into a newly created pid file at the same location.

Stop is similar, as in it works on the PID file. It will check if the process is running by checking the pid file, and if it does, it will run a kill command on the process.

Phew.

Setting this up for multiple systems is a pain, and it is more technical than I would like to be doing on a routine basis. Specifically, managing processes with PIDs and using the kill command makes me a little nervous.

But there are other problems I could run into that would run into some shortcomings of init.d. One being the ability to base the daemon’s start on the network interface being up, or the filesystem being ready. This would apply to applications such as web and SMTP servers.

Enter upstart.

Upstart came into play in 2006 (at least in the Ubuntu world). It is a replacement of the previously mentioned init system where scripts are placed in /etc/init.d and /etc/rc*.d folders. It has a more accurate boot sequence through event based start up, and take less effort to implement due to some tasks like PID management being automatically handled.

Upstarts are configured with stanzas.  Two of those being start and stop, where you use runlevels or events (network up, filesystem ready) to define when the daemon should be started and shutdown. When it’s all set it looks like this:

description “nginx http daemon”

# Start daemon when filestyem and network interface is up
start on (filesystem and net-device-up IFACE=lo)

# Stop daemon when runlevel is not specified levels
stop on runlevel [!2345]

# Daemon binary location
env DAEMON=/usr/sbin/nginx

# Daemon pid location
env PID=/var/run/nginx.pid

# Indicate daemon has child processes
expect fork

# Restart if daemon ends prematurely
respawn

# Max respwans
respawn limit 10 5

# Commands to run before daemon starts
pre-start script
$DAEMON -t
if [ $? -ne 0 ]
then exit $?
fi
end script

# Run daemon
exec $DAEMON

Conclusion

So there you have it. Upstarts make life easier by cutting your daemon initialization scripts in half with more control, and less being in the weeds. It’s ideal for custom or compiled applications (packages often install their own init scripts) and removes the need to boot up a daemon every time you start your machine.

A S.O.L.I.D Design

As mentioned in a previous post, I just recently led the launch of a search focused web application. It’s time now to reflect a bit on the techniques and technology used.

From the start I was looking for a supporting framework that was conducive for rapid development that did not sacrifice stability,  integrity, or consistency. I wanted a set of tools that not only allowed our developers to quickly build out features, but also avoid getting stuck “in the trenches” building out core function. My approach to accomplish this was leveraging a collection of object-oriented  principles, frameworks, and debugging tools. I’m going to break this up between those three since they are each interesting and important, starting with the principles I used for the project.

Principles

For me, commonly accepted design theories are ideas put to practice that have been vetted and adopted by the consensus. While it’s still important to be innovative and be a free-thinker, I believe in standing on the shoulders of giants; building from what is known to work. This does not limit the ability to be creative or do something different, but instead empowers by laying out benefits and avoided caveats through comprehending the principles.

Object-oriented design can be nebulous and feel vague, but this is the spirit of object-oriented architecture. Concepts are  abstract and isolated, which allow them to be  independently combined to make a whole. What’s important to take away is they are a means to an end: a solidly structured application that can efficiently be extended and maintained.

With that said, it is time to go over the concepts I went with, which can be place into three groups: S.O.L.I.D, MVC, and ORM. Both MVCs and ORMs seem to follow the S.O.L.I.D pattern, so there is overlay, but that doesn’t mean they are required to follow any of the S.O.L.I.D principles. As said before, object-oriented concepts are intended to be independently applied.

S.O.L.I.D

S.O.L.I.D has been around for about a decade. Practice of these concepts are prominent in many areas of application development. The easiest to identify for me are Java frameworks such as Struts and Spring, but I can also see  partial application in front-end web development, starting with the separation of HTML, JavaScript, and CSS. More modern JavaScript frameworks have carried the torch, achieving full application, and in turn evolving web pages into full-fledged web applications. While the application I built was server-side oriented, these concepts may still be applied to front-end web applications.

To me, what this all means is you have a system comprised of objects that each have a unique role.  They play nice with each other, and don’t get greedy and take over another components role. This is an awesome design pattern, because it keeps roles encapsulated and extensible. It reduces the chances of rogue code lying in wait. And by separating out roles and keeping objects decoupled, it is much easier to build new features without modifying core code that would results in testing and bugs.

MVC

Organizing the three key layers of a web application is essential to to keeping an orderly, and reusable codebase. Logic can be separate into at least three basic “buckets” by role: Model, View, and Controller. This structuring isn’t meant to be taken as absolute, and does not directly translate into a specific file structure.  There is code that will fall outside the model, controller, and view role,  such as components that handle routing and security. Instead, like other OO principles, it is a set of guidelines to help achieve a better codebase.

A basic web example of this is moving database queries into code that is under the model section of the application, and not mixing it in with HTML. Another example of  separating elements by role would be what became standard practice for front-end web development with the use of CSS, and external JavaScript files.

ORM

The interface in which data is accessed can dictate many design factors of the web application. An ORM allows data to be accessed and manipulated as normal objects. All business logic is encapsulated within the data object, instead of being strewn about the application. This means that data is accessed consistently throughout the application through a set of centralized objects and tools . While this concept introduces a level of complexity compared to straight queries or a light wrapper, the ability to work with data as a collection of objects is very powerful and clean.

Summary

This project was a test of how necessary it was to create a S.O.L.I.D application. The organization of code, and separation of roles had enormous benefits that kept me sane. Our course was not without trial and error. There were times these principles weren’t followed, and it resulted in fragile and inflexible components that haunted us later in the project.

There is a quote that I like that goes “There is no problem in computer science that cannot be solved by adding another layer of indirection, except having too many layers of indirection”. There is a conundrum of simplicity vs extensibility. Adding that extra layer all depends on what the desired endgame will be for the application, and it can be a difficult  judgement call.

Game Jam #7

Reeeally late in posting this, but I’m determined to post about my game jam back in July where the theme was time manipulation. The dynamic was a little different, I had an “idea person” to help move the creative process along and blocks. I was paired up with Jacq, sound engineer and creative mind. After a few iterations of rehashing the fundamentals of our game, we finally came up with a platformer that fit  the theme. From this experience I had some takeaways to apply to my next jam.

Idea People are AWESOME
Having a person to handle the brainstorming while you’re coding has its benefits. It’s easier to cut and run when hitting a wall, as the other person has already been thinking into alternatives, opposed to wasting time on something that just isn’t working because you don’t have any better ideas.

Skillsets can become dusty
This was a frustrating lesson to learn. After not touching Flixel for a month and a half, working with basics like movement and sprite placement was more difficult than it should have been.

There’s an easier way to prototype
My toolset has been pretty low level. I use ActionScript, and while I utilize the Flixel framework with libraries, it still requires a lot of coding. At the end of the jam I surmized I would have developed my prototype faster with a prototyping framework such as Construct 2 or Stencyl.  Both allow the rapid prototyping of platformers, such as this one without coding.

For those interested, the source and demo can be found here:
Source
Demo

« Go Back — View more posts »