Escalonamento, Migração de Recursos e
Balanceamento de carga
Carlos Ferrão Lopes nº M6935
Bruno Simões nº M6082
Celina Alexandre nº M6807
Paulo Cabral nº M6765
Quoc Nguyen-Trong nº M6831
Tecnologias de Cloud e Datacenter
Professor Doutor Nuno M. Garcia
Load Balancing
 Technology used to distribute service requests to resources.
 Load Balancing is an optimization technique in order to
increase utilization, yield, lowest latency, response time
reduction and prevent the system overload.
 This can be implemented in hardware – e.g.: F5 BigIP
Servers
 And can also be implemented in software – e.g.: Apache
mod_proxy_balancer extension
Load Balacing
 The following network resources can be load balanced:
 Network Interfaces and services such as DNS, FTP, and
HTTP
 Connections (using intelligent switches)
 Storage Resources
 Access to application instances
Load Balancing
 Without Loud Balancing would be very difficult to manage
the cloud (in a strand of requests VS resources).
 Load balancing provides redundancy needed to make an
unreliable system into trusted through the redirection of
resources by the machines.
 In addition a grouping with a failover mechanism provides an
increased tolerance to failures.
Load Balancing
 Operating principles
 In simpler load-balancing mechanisms:
 The Loud Balancing is listening on a network port for requests
for services
 When a client makes a request, it uses a scheduling algorithm
to allocate where the request shall be sent
Load Balancing
 Typical algorithms of timing:
 Round-Robin
 Weighted – Round Robin
 Dynamic Round Robin
 Fastest response Time
 Least Connections
Load Balancing - Algorithms
Fastest Response Time

The server is chosen based on the faster response time of a group of
servers.

This method can be particularly useful in environments where the servers
are distributed in different logical networks.
It’s possible only because of a good load
balancing mechanism…
/*Just for fun*/

[longman] Mechanism:
um sistema que se destina a
alcançar algo ou resolver
um problema
Load Balancing - Mechanisms
Internet
WAN
Firewall
 Balanceamento de carga é executadoSwitch
pelo balanceadores de carga,
usando algoritmos de agendamento.
Load balancer
LAN
Switch
Server 1
Server 2
Server 3
Load Balancing - Mechanisms
 Balanceamento de carga é executado pelo balanceadores de carga, usando
algoritmos de agendamento.
hardware-based
service-based
Load Balancing - Mechanisms
…exemplo do balanceador de carga baseada em hardware:
Load Balancing - Mechanisms
…service-based load balancer example:
Load Balancing - Mechanisms

Balanceamento de carga é executado pelo balanceadores de carga,
usando algoritmos de agendamento.
 Algoritmos de agendamento :

Estática: não há troca de informações entre o balanceador de carga e
cada nó de servidor, por isso tem um limite na condução correta do
balanceamento.

Dinâmica: rotear solicitações do cliente de acordo com as informações
dos nós do servidor.
Load Balancing - Algorithms
 Algoritmos de agendamento estáticos incluem (normalmente):



Round-Robin: atribui os pedidos para os servidores do modo Round-Robin
Least-Connection: encaminhar as solicitações para o servidor que tenha o
mínimo de conexões
Weighted Round-Robin and Weighted Least-Connection: Dá o “peso” de cada
nó de servidor
 Algoritmos de agendamento dinâmicos incluem (normalmente):



Agent-based Sophisticated and Scalable Scheduling Method (ABSS)
Agent-based Sophisticated Scheduling Mechanism by Using Memory
Utilization (ASSUM)
Dynamic Round-Robin
Load Balancing - Algorithms
Round-Robin
 Um dos métodos mais simples para distribuir solicitações do cliente
através de um grupo de servidores.

Round-Robin manner: O balanceador de carga encaminha as solicitações
de cliente para cada servidor á vez. Quando atingir o final da lista, o
balanceador de carga volta ao começo.
 Classificação do método Round-Robin :



Static
Weighted
Dynamic
Load Balancing - Algorithms
Static Round-Robin
 O balanceador de carga percorre uma fila circular
representativa de servidores, divide e envia as
solicitações do cliente para cada servidor antes de
chegar ao início da fila para começar de novo.
 Funciona bem quando todos os servidores têm a mesma
capacidade.
Load Balancing - Algorithms
Static Round-Robin
Client
A, B, C, A, B, C, and so on
Load
balancer
1
Server
A
2
Server
B
3
Server
C
Load Balancing - Algorithms
Weighted Round-Robin

É atribuída um peso para cada servidor com base em critérios escolhidos
pelo administrador.

O critério mais comumente usado é a capacidade de manipulação de tráfego
do servidor. O balanceador de carga faz uma solicitação HTTP e a medida
de quão rápida que um servidor responde a ele.

Quanto maior o peso, maior a proporção de solicitações de clientes o
servidor recebe.
Load Balancing - Algorithms
Weighted Round-Robin
Client
A, B, B, C, A, B, B, C, and so on
Load
balancer
1
Server
A
2
3
Server
B
4
Server
C
Load Balancing - Algorithms
Dynamic Round-Robin

Um peso é atribuído a cada servidor dinamicamente, com base em dados
em tempo real sobre o estado atual do servidor, portanto, o peso é
alterado continuamente.

Um método dinâmico de balanceamento de carga, distribuindo os pedidos
com base em vários aspetos da análise de servidor em tempo real, tais
como o número atual de conexões por servidor ou o mais rápido tempo
de resposta do servidor.
Load Balancing - Algorithms
Least Connections

With this method the system consider connections with a server that has
the least number of current connections.

Least Connections works best in environments where the servers and/or
equipment have similar capabilities.

Concluding, this algorithm only keeps track of the number of links
attached to each server.

Selecting the one with the fewest
Load Balancing - Algorithms
Observed

This method uses a combination of logic used in the Least connections
algorithms and Fastest response.

In this method the servers that have a better balance: fewer connections
and faster response time.

Receive a larger proportion of links
Load Balancing - Algorithms
Predictive

The Predictive uses the classification method used by the algorithm
Observed.

However, with this algorithm it is possible to analyze the trend of ranking
over time:


Determine whether the performance of one or more servers is improving or
getting worse.
The ranked servers with a better performance rating, rather than worsen,
receive a higher proportion of links.
Load Balancing - Algorithms
Random

This method of load balancing distributes randomly the load between
available servers.

Chooses random numbers (assigned to different servers) and sends the
current connection to the chosen.

This method is available in many implementations of load balancing.

However, his utility is questionable.
Load Balancing - Conclusions

Having examined the different balancing algorithms we can conclude:
 Load-balancing systems more sophisticated manage differently the
workload requested and/or allocated by customers based on different
factors:

Response time

Waiting lists

Connection latency and capacity
Load Balancing
Thank you
Obrigado