[SOLVED] SER334 Module 7 Implementing Load Balancing

Arizona State University SER334: Operating Systems & System Programming
TA Khan, Asst. Teaching Professor Acua Revised 4/1/2023
Implementing Load Balancing
Summary: In this homework, you will be implementing the main multi-threaded logic for doing batchbased
server load balancing using mutexes.
1 Background
In this assignment, you will write a batch-based load balancer. Consider a server that handles data processing
based on user requests. In general, a server has only a xed set of hardware resources that it can use to
satisfy user requests. This is problematic since servers can become overloaded. One common scaling feature
that is implemented is load batching (a form of load balancing). On modern platforms, it is possible to
spin up a virtual instance server using a cloud environment (e.g., AWS, Microsoft Azure, Google Cloud) to
handle specic needs. The idea of cloud computing has gained traction as a way to deal with scalability and
maintenance issues. Examples include internet-based storage, computing, or services, which are accessed by
client-based devices or by web browsers. As more requests are made, more servers instance are spawned.
This gives the ability to seamlessly scale up to peaks in user requests. Although this provides a good way
to scale resources, the cost of spinning up a new server is non-trivial. Thus, gateway servers tend to collect
a batch of requests before starting a server instance. Your goal in this assignment is to implement the
multi-threaded load balancer server logic that will mimic the process of creating server instances to process
batches of requests as they come in. Note that while this system is conceptually a network situation, we will
be modeling it as a set of functions spread across three les.
At a high level, the load balancer server waits for a specic number of requests to be made before spawning
an instance server in a cloud-like environment, and initializing the instance with the appropriate work. We
call the number of requests that should be serviced the batch size, and assume that the server instances are
designed so they can handle exactly batch size number of requests at a time. The load balancer starts to
form a batch as soon as it receives as least one request and continues to add requests to the batch until
the batch is full (i.e., the batch size is reached). At that point, the load balancer will spawn a new server
instance using the instance host to begin processing the batch. The load balancer makes sure that server
instances are only initialized when enough requests have been made. Internally, the load balancer will add
requests to a list which is then forwarded to an instance server once it reaches the appropriate size. As the
requests are handled by the individual server instances, each instance will store the result into an output
location given by the creator of the request.
This document is separated into ve sections: Background, System Architecture, Requirements, Include
Files, and Submission. You have almost nished reading the Background section already. In System Architecture,
we discuss the conceptual view of the system as the interactions between users, a load balancer, and
an instance host. In Requirements, we will discuss what is expected of you in this homework. In Include
Files, we discuss the the various libraries and function calls you may nd useful in the assignment. Lastly,
Submission discusses how your source code should be submitted on Canvas.
2 System Architecture
Conceptually, the system is divided into three main components: users, the load balancing server, and the
server instance host. Figure 1 shows these components and how they are related.
1. User: A user is a person who utilizes the system to get a job done. Users make requests to the load
balancer server. A request consists of the id of the user, some data payload, and a place to store the
result of processing. A request is also called a job. On completion of the request from the server, the
result (which will be computed by some instance) will be stored in the location specied in the request.
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2. Load Balancer Server: The load balancer server acts as a gateway that is a middle layer between
server instances and the users, it is used to distribute incoming trac to dierent servers capable of
fullling those requests in a manner that maximizes throughput, and ensures that no one server is
overworked.
3. Server Instance Host: The server instance host is a cloud-like environment that can dynamically
create server instances to deliver resources (e.g., compute time) on demand. Changes to one server
instance do not have any eect on other instances. Unlimited server instances can be run within a host
environment at any given time. Each server instance takes a batch of requests, and processes it.
Figure 1: Structural overview of the system containing users, a load balancer, and a server host.
Figure 2 shows an overview of the system ow. Behaviorally, the load balancer rst receives requests from
users. Once the load balancer has received enough requests, it adds the requests to a batch, instantiates a
new server instance, and sends the batch to it. After a batch has been received, it is processed, and the
results are saved where the user specied.
Figure 2: Behavioral overview depicting how system elements communicate.
2.1 System Model
For this scenario, we will not be implementing a full networked solution of dierent programs running across
multiple computers, but rather model it as a set of functions spread across dierent les. The implementation
will be done using three les that provide the functionality needed by each of the system components. For
example, we will have a le called InstanceHost.c which contains a function called host_request_instance().
When the load balancer in our system needs to create an instance, it will simply call host_request_instance()
from InstanceHost.c. It will not make any sort of network connection. The goal is simply to use C functions
that t into the overall conceptual framework given by the problem.
The network will be modeled using three les. User.c will receive input for the amount of users making
requests, and the batch size. During execution, a thread will be generated to represent each user request.
Each request will be passed to LoadBalancer.c. LoadBalancer.c, after receiving requests from User.c, will
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construct a batch (a linked list). The batch will be passed to InstanceHost.c which will remove the requests
from the batch, and process it. Batches will be represented as a linked list of nodes, with nodes containing
the pieces of information (id, data, result address) required by each request. Note that a job will simply
consist of squaring a number.
3 Requirements [40 points]
For your submission will you create two new les: LoadBalancer.c (which includes LoadBalancer.h, and
InstanceHost.h), and InstanceHost.c (which includes InstanceHost.h). You will not need to make changes
to User.c, LoadBalancer.h, or InstanceHost.h. Your task is to implement the functionality as dened in
LoadBalancer.h and Instance.h in their respective .c les. As a base requirement, your program must
compile and run under Xubuntu (or another variant of Ubuntu) 22.04.
The number of requests (N) and batch size (K) will be provided as an input during execution. Each
request will run on an individual thread. Requests will be received by the load balancer which will instantiate
new server instances depending on batch size. The LoadBalancer will create a linked list (up to size K) as
requests are made and which will be protected by a mutex to ensure only one request is added at a time.
After a batch has been lled, the batch is sent to a new server instance. Once in a thread on the host, the
linked list’s requests are processed and the results are given as an output. Throughout the lifetime of the
program, create only one LoadBalancer and one InstanceHost object. Global variables not permitted for
LoadBalancer or InstanceHost.
1. LoadBalancer.c: A le containing a set of functions to simulate a load balancer. [21 points total]
(a) balancer* balancer_create(int batch_size): Initializes the load balancer. Takes batch size as parameter.
[3 points]
(b) void balancer_destroy(balancer** lb): Shuts down the load balancer. Ensures any outstanding
batches have completed. [3 points]
If there are leftover jobs (too few to have spawned an instance host normally), then create an
instance host to handle them. [5 points]
(c) void balancer_add_job(balancer* lb, int user_id, int data, int* data_return): Adds a job to the
load balancer. The linked list of jobs must be protected by a mutex. [6 points]
If enough jobs have been added to ll a batch, the load balancer will request a new instance
from InstanceHost. [5 points]
2. InstanceHost.c: A le containing a set of functions to simulate a cloud-like server instance host. [17
points total]
(a) host* host_create(): Initializes the host environment. [4 points]
(b) void host_destroy(host** h): Shuts down the host environment. Ensures any outstanding batches
have completed. [3 points]
(c) void host_request_instance(host* h, struct job_node* batch): Creates a new server instance (i.e.,
thread) to handle processing the items contained in a batch (i.e., a listed list of job_node). Server
instances are modeled as threads that process a list of jobs. [6 points]
Data must be processed (the data value squared) and returned to the user (using the result
pass-by-reference). [5 points]
You may add other helper functions as needed.
Sample Output
User #1: Wants to pr o c e s s data=77 and s t o r e i t at 0xb2a00470 .
LoadBalancer : Received new job from us e r #1 to pr o c e s s data=77 and s t o r e i t at 0xb2a00470 .
User #4: Wants to pr o c e s s data=49 and s t o r e i t at 0 xb2c00480 .
LoadBalancer : Received new job from us e r #4 to pr o c e s s data=49 and s t o r e i t at 0 xb2c00480 .
User #5: Wants to pr o c e s s data=62 and s t o r e i t at 0 x95f89c0 .
LoadBalancer : Received new job from us e r #5 to pr o c e s s data=62 and s t o r e i t at 0 x95f89c0 .
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User #8: Wants to pr o c e s s data=40 and s t o r e i t at 0 x95f89d0 .
LoadBalancer : Received new job from us e r #8 to pr o c e s s data=40 and s t o r e i t at 0 x95f89d0 .
User #3: Wants to pr o c e s s data=93 and s t o r e i t at 0 x95f89b0 .
LoadBalancer : Received new job from us e r #3 to pr o c e s s data=93 and s t o r e i t at 0 x95f89b0 .
LoadBalancer : Received batch and spinning up new ins t anc e .
User #9: Wants to pr o c e s s data=72 and s t o r e i t at 0xb2a004a0 .
LoadBalancer : Received new job from us e r #9 to pr o c e s s data=72 and s t o r e i t at 0xb2a004a0 .
User #7: Wants to pr o c e s s data=63 and s t o r e i t at 0 xb2c00490 .
LoadBalancer : Received new job from us e r #7 to pr o c e s s data=63 and s t o r e i t at 0 xb2c00490 .
User #6: Wants to pr o c e s s data=90 and s t o r e i t at 0xb2a00490 .
LoadBalancer : Received new job from us e r #6 to pr o c e s s data=90 and s t o r e i t at 0xb2a00490 .
User #0: Wants to pr o c e s s data=83 and s t o r e i t at 0 xb2c00470 .
LoadBalancer : Received new job from us e r #0 to pr o c e s s data=83 and s t o r e i t at 0 xb2c00470 .
User #2: Wants to pr o c e s s data=86 and s t o r e i t at 0xb2a00480 .
LoadBalancer : Received new job from us e r #2 to pr o c e s s data=86 and s t o r e i t at 0xb2a00480 .
LoadBalancer : Received batch and spinning up new ins t anc e .
User #0: Received r e s u l t from data=83 as r e s u l t =6889.
User #3: Received r e s u l t from data=93 as r e s u l t =8649.
User #6: Received r e s u l t from data=90 as r e s u l t =8100.
User #1: Received r e s u l t from data=77 as r e s u l t =5929.
User #8: Received r e s u l t from data=40 as r e s u l t =1600.
User #5: Received r e s u l t from data=62 as r e s u l t =3844.
User #4: Received r e s u l t from data=49 as r e s u l t =2401.
User #7: Received r e s u l t from data=63 as r e s u l t =3969.
User #2: Received r e s u l t from data=86 as r e s u l t =7396.
User #9: Received r e s u l t from data=72 as r e s u l t =5184.
This output was generated with 10 user requests and a batch size of 5. Since the users make requests
after waiting a random amount of time your output will dier. To get this output, you will need to add two
lines to your lines:
// as f i r s t l i n e o f balancer_add_job :
p r i n t f (” LoadBalancer : Received new job from us e r #%d to pr o c e s s data=%d and
s t o r e i t at %p . \ n” , user_id , data , data_return ) ;
// as f i r s t l i n e o f hos t_r eque s t_ins tanc e :
p r i n t f (” LoadBalancer : Received batch and spinning up new ins t anc e . \ n ” ) ;
3.1 Basecode
For this assignment, three base les are provided: User.c, LoadBalancer.h, and InstanceHost.h. These les
together make up the logic of our system.
1. User.c: A program to simulate multiple users simultaneously requesting work (a “job”) to be carried
by a load balancing server and returned to the user. A job is to compute the square of a number.
(a) int main(): Entry point to simulation.
(b) void* simulate_user_request(void* user_id): simulates a user requesting work to be done a
server.
2. LoadBalancer.h: A le containing denitions for a set of functions to simulate a load balancer.
(a) void balancer_init(int batch_size): Initializes the load balancer.
(b) void balancer_shutdown(): Shuts down the load balancer.
(c) void balancer_add_job(int user_id, int data, int* data_return): Adds a job to the load balancer.
3. InstanceHost.h: A le containing denitions for a set of functions to simulate a cloud-like server
instance host.
(a) void host_init(): Initializes the host environment.
(b) void host_shutdown(): Shuts down the host environment.
(c) void host_request_instance(struct job_node* batch): Creates a new server instance to handle
processing the items contained in a batch.
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4 Include Files
To complete this assignment, you may nd the following include les useful:
pthread.h: Denes functionality for manipulating mutexes.
 Useful functions
* int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *attr): function
initializes the mutex referenced by mutex with attributes specied by attr.
* int pthread_mutex_lock(pthread_mutex_t *mutex): The mutex object referenced by mutex
is locked by calling pthread_mutex_lock(). If the mutex is already locked, the calling thread
blocks until the mutex becomes available.
* int pthread_mutex_unlock(pthread_mutex_t *mutex): The pthread_mutex_unlock() function
releases the mutex object referenced by mutex.
* int pthread_mutex_destroy(pthread_mutex_t *mutex): The pthread_mutex_destroy() function
shall destroy the mutex object referenced by mutex; the mutex object becomes, in eect,
uninitialized.
5 Submission
The submission for this assignment has one part: a source code submission. The le should be attached to
the homework submission link on Canvas.
Writeup: For this assignment, no write up is required.
Source Code: Please name your classes as “LastnameLoadBalancer.c”, and LastnameInstanceHost.c
(e.g., “KhanLoadBalancer.c”, and KhanInstanceHost.c). (If you require additional .c or .h les, please
check with the instructor or TA rst.)
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