Distributes queued requests across a dynamically sized pool of WebServer objects. More...

#include <LoadBalancer.h>

Public Member Functions
	LoadBalancer (std::string name, std::size_t initialServers, const ScalingPolicy &policy, const Firewall &firewall, std::size_t maxQueue, Logger &logger)
	Creates a load balancer with an initial server pool.
bool	admit (const Request &request, unsigned long cycle)
	Offers a request to the load balancer.
void	start ()
	Records the starting queue size and performs the first dispatch at time 0.
void	processCycle (unsigned long cycle, const std::vector< Request > &arrivals)
	Runs one clock cycle: complete work, admit arrivals, adjust capacity, dispatch.
void	recordSnapshot (unsigned long cycle)
	Saves a Snapshot of the current state for the periodic table in the log.
std::string	statusLine (unsigned long cycle) const
	Builds a one-line status: queue, servers (busy/idle/retiring), completed, rejected.
void	summarize (std::ostream &out) const
	Writes the end-of-run summary for this load balancer.
const std::string &	name () const
std::size_t	queueSize () const
std::size_t	liveServers () const
std::size_t	activeServers () const
std::size_t	busyServers () const
std::size_t	idleServers () const
std::size_t	retiringServers () const
std::size_t	inService () const
const LoadBalancerStats &	stats () const
const std::vector< ScaleEvent > &	scaleEvents () const
const std::vector< Snapshot > &	snapshots () const
const std::vector< WebServer > &	servers () const
const ScalingPolicy &	policy () const
const Firewall &	firewall () const

Detailed Description

Distributes queued requests across a dynamically sized pool of WebServer objects.

The load balancer owns a FIFO queue of pending Request values and a vector of WebServer objects. For each clock cycle, processCycle() performs these steps in order:

Complete work - every busy server advances one cycle; finished requests are counted and retiring servers that became idle are removed.
Admit arrivals - each new request passes through the Firewall; allowed requests join the back of the queue.
Adjust capacity - every ScalingPolicy::cooldownCycles cycles the queue size is compared with the number of active servers and one server may be added or retired.
Dispatch - the oldest queued requests are assigned to idle, non-retiring servers in server-id order.

Scale-down prefers removing an idle server. If every server is busy, one is marked retiring so that it finishes its request before removal; no request is ever lost when capacity shrinks.

Definition at line 116 of file LoadBalancer.h.

Constructor & Destructor Documentation

◆ LoadBalancer()

LoadBalancer::LoadBalancer	(	std::string	name,
		std::size_t	initialServers,
		const ScalingPolicy &	policy,
		const Firewall &	firewall,
		std::size_t	maxQueue,
		Logger &	logger )

Creates a load balancer with an initial server pool.

Parameters

name	Short name used in log lines, for example "LB" or "LB-P".
initialServers	Number of servers created at time 0 (at least 1).
policy	Scaling thresholds, cooldown and server limits.
firewall	Blocked IP ranges applied in admit().
maxQueue	Largest allowed queue size; 0 means unlimited.
logger	Destination for event and status messages.

Definition at line 15 of file LoadBalancer.cpp.

Member Function Documentation

◆ admit()

bool LoadBalancer::admit	(	const Request &	request,
		unsigned long	cycle )

Offers a request to the load balancer.

The request is rejected if its source IP is blocked, discarded if the queue is full, and otherwise appended to the queue.

Parameters

request	Request to admit.
cycle	Current clock cycle, for logging.

Returns: True if the request was queued.

Definition at line 36 of file LoadBalancer.cpp.

◆ start()

void LoadBalancer::start ( )

Records the starting queue size and performs the first dispatch at time 0.

Call once after the initial queue has been admitted and before the first processCycle().

Definition at line 61 of file LoadBalancer.cpp.

◆ processCycle()

void LoadBalancer::processCycle	(	unsigned long	cycle,
		const std::vector< Request > &	arrivals )

Runs one clock cycle: complete work, admit arrivals, adjust capacity, dispatch.

Parameters

cycle	Clock cycle being simulated (1, 2, 3, ...).
arrivals	Requests generated during this cycle.

Definition at line 70 of file LoadBalancer.cpp.

◆ recordSnapshot()

void LoadBalancer::recordSnapshot ( unsigned long cycle )

Saves a Snapshot of the current state for the periodic table in the log.

Parameters

cycle Current clock cycle.

Definition at line 218 of file LoadBalancer.cpp.

◆ statusLine()

std::string LoadBalancer::statusLine ( unsigned long cycle ) const

Builds a one-line status: queue, servers (busy/idle/retiring), completed, rejected.

Parameters

cycle Current clock cycle.

Returns: Status text without color codes.

Definition at line 231 of file LoadBalancer.cpp.

◆ summarize()

void LoadBalancer::summarize ( std::ostream & out ) const

Writes the end-of-run summary for this load balancer.

Parameters

out	Stream to write to.

Definition at line 240 of file LoadBalancer.cpp.

◆ name()

const std::string & LoadBalancer::name ( ) const

Returns: Name used in logs.

Definition at line 297 of file LoadBalancer.cpp.

◆ queueSize()

std::size_t LoadBalancer::queueSize ( ) const

Returns: Requests waiting in the queue.

Definition at line 299 of file LoadBalancer.cpp.

◆ liveServers()

std::size_t LoadBalancer::liveServers ( ) const

Returns: All servers, including retiring ones.

Definition at line 301 of file LoadBalancer.cpp.

◆ activeServers()

std::size_t LoadBalancer::activeServers ( ) const

Returns: Servers that accept new work (not retiring).

Definition at line 303 of file LoadBalancer.cpp.

◆ busyServers()

std::size_t LoadBalancer::busyServers ( ) const

Returns: Servers currently processing a request.

Definition at line 308 of file LoadBalancer.cpp.

◆ idleServers()

std::size_t LoadBalancer::idleServers ( ) const

Returns: Servers with no request in progress.

Definition at line 313 of file LoadBalancer.cpp.

◆ retiringServers()

std::size_t LoadBalancer::retiringServers ( ) const

Returns: Servers marked for removal after their current request.

Definition at line 315 of file LoadBalancer.cpp.

◆ inService()

std::size_t LoadBalancer::inService ( ) const

Returns: Requests currently being processed.

Definition at line 320 of file LoadBalancer.cpp.

◆ stats()

const LoadBalancerStats & LoadBalancer::stats ( ) const

Returns: Run counters.

Definition at line 322 of file LoadBalancer.cpp.

◆ scaleEvents()

const std::vector< ScaleEvent > & LoadBalancer::scaleEvents ( ) const

Returns: Every change made to the server pool.

Definition at line 324 of file LoadBalancer.cpp.

◆ snapshots()

const std::vector< Snapshot > & LoadBalancer::snapshots ( ) const

Returns: Snapshots recorded with recordSnapshot().

Definition at line 326 of file LoadBalancer.cpp.

◆ servers()

const std::vector< WebServer > & LoadBalancer::servers ( ) const

Returns: The live servers in id order.

Definition at line 328 of file LoadBalancer.cpp.

◆ policy()

const ScalingPolicy & LoadBalancer::policy ( ) const

Returns: The scaling policy in use.

Definition at line 330 of file LoadBalancer.cpp.

◆ firewall()

const Firewall & LoadBalancer::firewall ( ) const

Returns: The firewall in use.

Definition at line 332 of file LoadBalancer.cpp.

The documentation for this class was generated from the following files:

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

◆ LoadBalancer()

Member Function Documentation

◆ admit()

◆ start()

◆ processCycle()

◆ recordSnapshot()

◆ statusLine()

◆ summarize()

◆ name()

◆ queueSize()

◆ liveServers()

◆ activeServers()

◆ busyServers()

◆ idleServers()

◆ retiringServers()

◆ inService()

◆ stats()

◆ scaleEvents()

◆ snapshots()

◆ servers()

◆ policy()

◆ firewall()