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niklas 2011-05-12 13:08:00 +02:00
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8
bibliography.bib
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@ -192,6 +192,14 @@
URL = "http://www.theesa.com/facts/index.asp"
}
@article {Dictionary.com2011,
title = {Merriam-Webster's Dictionary},
month = {May},
day = {12},
year = {2011},
url = {http://dictionary.reference.com/browse/fault+tolerance},
}
@article{Armstrong:2010:ERL:1810891.1810910,
author = {Armstrong, Joe},

132
report.lyx
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@ -662,7 +662,14 @@ textbf{Software failiure}}{A failiure in software (the GGS, the operating
\end_layout
\begin_layout Section
Background
Background
\begin_inset CommandInset label
LatexCommand label
name "sec:Background"
\end_inset
\end_layout
\begin_layout Standard
@ -2310,7 +2317,7 @@ The GGS is a game server.
A game should not only be able to vary in terms of genre, graphics, gameplay
etc, but also in the way the game is implemented for example in different
programming languages.
The GGS should be OS independent and run on Windows, OSX and Linux.
The GGS should be OS independent and run on Windows, OS X and Linux.
The GGS can be run as a listen server on the players computer and host
games locally.
It could also be a dedicated server running on dedicated independent hardware.
@ -2319,18 +2326,29 @@ The GGS is a game server.
\end_layout
\begin_layout Standard
Another aspect was the desire to let a client upload the source code of
the game it would like to play on the GGS.
Another aspect is the desire to let a client upload the source code of the
game it would like to play on the GGS.
This way every client could connect to the server and install the game
through a
\begin_inset CommandInset nomenclature
LatexCommand nomenclature
symbol "API"
description "Application programming interface"
through a API without the need of installation through the server provider
or maintainer.
\end_layout
\begin_layout Standard
\begin_inset ERT
status open
\begin_layout Plain Layout
\backslash
nomenclature{
\backslash
textbf{API}}{Application programming interface}
\end_layout
\end_inset
without the need of installation through the server provider or maintainer.
\end_layout
\begin_layout Section
@ -2345,17 +2363,36 @@ name "sec:Fault-Tolerance"
\end_layout
\begin_layout Standard
Fault tolerance is an important factor in all servers, a server that is
fault tolerant should be able to follow a given specification when parts
of the system fails.
Merriam-Webster’s dictionary
\begin_inset CommandInset citation
LatexCommand citeyearpar
key "Dictionary.com2011"
\end_inset
defines fault tolerance as:
\end_layout
\begin_layout Quotation
1.
The ability of a system or component to continue normal operation despite
the presence of hardware or software faults.
This often involves some degree of redundancy.
\end_layout
\begin_layout Quotation
2.
The number of faults a system or component can withstand before normal
operation is impaired.
\end_layout
\begin_layout Standard
Fault tolerance is an important factor in servers, a server that is fault
tolerant should be able to follow a given specification when parts of the
system fail.
This means that fault tolerance is different in each system depending on
what specification they have.
A system could be fault tolerant in different aspects, one is where the
system is guaranteed to be available but not safe and it could also be
reversed, that the system is safe but not guaranteed to be available.
Depending on the system one property may be more important.
A system could also have non existent fault tolerance or it could be both
safe and guaranteed to be available.
what specification it has.
It should be noted that it is not possible to achieve complete fault tolerance,
a system will always have a certain risk of failure.
With this in mind the goal is to make the GGS prototype as fault tolerant
@ -2365,14 +2402,14 @@ Fault tolerance is an important factor in all servers, a server that is
\begin_layout Standard
In order to make the GGS prototype fault tolerant the programming language
Erlang has been used.
Erlang will not guarantee a fault tolerant system but it has features that
support and encourage the development of fault tolerant systems.
In the GGS it is important that the system overall is fault tolerant and
not small parts only.
Erlang will not guarantee a fault tolerant system, however it has features
that support and encourage the development of fault tolerant systems.
In the GGS it is important that the complete system is fault tolerant,
not only small parts.
Crashes of the whole system should be avoided as this would make the system
unusable for a time.
By using supervisor structures it is possible to crash and restart small
parts of the system, this is convenient as fault can be handled within
parts of the system, this is convenient as faults can be handled within
small modules thus never forcing a crash of the system.
\end_layout
@ -2479,7 +2516,7 @@ name "sec:Scalability"
\begin_layout Standard
Each instance of the GGS contains several tables.
Each table is an isolated instance of a game, for example a chess game
Each table is an isolated instance of a game, for instance a chess game
or a poker game.
The way that the GGS scales is to distribute these tables on different
servers.
@ -2490,11 +2527,11 @@ Each instance of the GGS contains several tables.
down at a new table, all within the same game session.
Therefore, the main focus of the GGS is not to move players among tables,
but to keep a player in a table, and to start new tables instead.
When a server has reached a certain number of players the performance will
start to decrease.
When a server reaches a certain number of players the performance will
start to decrease, or worse, the server may even crash.
To avoid this the GGS will start new tables on another server, using this
technique the players will be close to evenly distributed among the servers.
It is important to investigate and find out how many players that are optimal
It is important to investigate and find out how many players are optimal
for each server.
This approach makes it possible to use all resources with moderate load,
instead of having some resources with heavy load and some with almost no
@ -2502,16 +2539,23 @@ Each instance of the GGS contains several tables.
\end_layout
\begin_layout Standard
As mentioned in the purpose section there are two different types of scalability
, structural scalability and load scalability.
As mentioned in section
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:Background"
\end_inset
there are two different types of scalability, structural scalability and
load scalability.
To make the GGS scalable both types of scalability are needed.
Structural scalability means in our case that it should be possible to
add more servers to an existing cluster of servers.
By adding more servers the limits of how many users a system can have is
increased.
Load scalability in contrast to structural scalability is not about how
to increase the actual limits of the system.
Instead it means how good the system handles increased load.
to increase the actual limits of the system, rather it means how good the
system handles increased load.
The GGS should be able to scale well in both categories.
\end_layout
@ -2522,12 +2566,11 @@ Load balancing
\begin_layout Standard
The need for load balancing varies among different kind of systems.
Small systems that only use one or a couple of servers can cope with a
simple implementation of it, while in large systems it is critical to have
extensive and well working load balancing.
The need also depends on what kind of server structure that the system
works on.
A static structure where the number of servers are predefined or a dynamic
structure where the number varies.
simple implementation of load balancing, while in large systems it is useful
to have extensive and well working load balancing.
The need also depends on what kind of server structure the system works
on, a static structure where the number of servers are predefined or a
dynamic structure where the number varies.
\begin_inset ERT
status open
@ -2546,7 +2589,7 @@ textbf{Amazon EC2}}{A cloud computation service}
\end_layout
\begin_layout Standard
Load balancing and scaling is difficult in different scenarios.
Load balancing and scaling are difficult in different scenarios.
When running in a separate server park, there are a set number of servers
available, this means that an even distribution on all servers is preferable.
When running the GGS in a cloud, such as Amazon EC2, it is possible to
@ -2578,7 +2621,7 @@ How do we distribute load on these new servers?
\begin_layout Standard
Load balancing is a key component to achieve scalability in network systems.
The GGS is a good example of a system that needs to be scalable, to attain
this load balancing is necessary.
this, load balancing is necessary.
Optimization of the load balancing for a system is an important task to
provide a stable and fast load balancer.
There are certain persistence problems that can occur with load balancing,
@ -3061,18 +3104,19 @@ Security
\end_layout
\begin_layout Standard
We only support languages running in a sandboxed environment.
The GGS only supports languages running in a sandboxed environment.
Each game session is started in its own sandbox.
The sandboxing isolates the games in such a way that they cannot interfere
with each other.
If sandboxing was not in place, one game could potentially modify the contents
of a different game.
A similar approach is taken with the persistent storage we provide.
A similar approach is taken with the persistent storage provided by the
GGS.
In the storage each game has its own namespace, much like a table in a
relational database.
A game is not allowed to venture outside this namespace, and can because
this not modify the persistent data of other games.
of this not modify the persistent data of other games.
\begin_inset ERT
status open