A large number of scheduling and allocation policies are proposed in literature. While, scheduling is required for speeding up the execution, allocation policy is used for proper resource management and improving resource performance. The strength of the load balancing algorithm is determined by the efficacy of the scheduling algorithm and the allocation policy .

If you’re watching a Netflix video, it doesn’t matter that you have two or three cellular connections plus the RV park’s WiFi, unless you can use them all at the same time. Also it provides a layer of abstraction to the user and prevents him from being affected even if particular servers in the group are changed or removed from the group. There is cool engineering involved in ensuring proper TCP connection tracking across multiple Load Balancer nodes. It solves an in-memory distributed consensus problem across all customer defined NLBs with million TPS possible per NLB. Katran is the component that decides the final destination of a packet addressed to a VIP so the network needs to route packets to Katran first. This requires the network topology to be L3 based, e.g., packets are routed by IP rather than by MAC addresses.

Task Load balancing is the act of distribution of tasks across the VMs from overloaded machines to under loaded machines. Server LB is proper distribution of total incoming load in a datacenter or a server farm across the servers. Network LB is concerned with management of incoming traffic without use of complex protocols. Further on the basis of mode of execution of tasks, dynamic algorithms are grouped as offline mode also called as batch mode and online mode or live mode as shown in Fig.3. In batch mode, the task is allocated only at some predefined instances where as in online mode the user task is mapped to a VM as soon it enters the scheduler. Dynamic load balancing algorithms are comparatively complex algorithms in contrast with their counterparts that handle incoming traffic flow at run time and can change state of a running task at any point of time.

Citrix ADC goes beyond load balancing to provide holistic visibility across multi-cloud, so organizations can seamlessly manage and monitor application health, security, and performance. A load balancer, or the ADC that includes it, will follow an algorithm to determine how requests are distributed across the server farm. There are plenty of options in this regard, ranging from the very simple to the very complex. Load balancers should ultimately deliver the performance and security necessary for sustaining complex IT environments, as well as the intricate workflows occurring within them. In this method, the load balancer looks at the bandwidth consumption of servers in Mbps for the last fourteen seconds.

How The Http Load Balancer Works

There is a variety of load balancing methods, which use different algorithms best suited for a particular situation. The load balancer merely passes an encrypted request to the web server. But organizations that require extra security may find the extra overhead worthwhile. This is why load balancers are an essential part of an organization’s digital strategy. When you insert NGINX Plus as a load balancer in front of your application and web server farms, it increases your website’s efficiency, performance, and reliability.

Figure3 shows the load balancing taxonomy on the basis of nature and state of algorithm. From the sticky information, the load balancer plug-in first determines the instance to which the request was previously forwarded. If that instance is found to be healthy, the load balancer plug-in forwards the request to that specific application server instance.

A relatively simple algorithm, the least bandwidth method looks for the server currently serving the least amount of traffic as measured in megabits per second . Similarly the least packets method selects the service that has received the fewest packets in a given time period. The ability to divert traffic to a passive server temporarily also allows developers the flexibility to perform maintenance work on faulty servers. You can point all traffic to one server and set the load balancer in active mode.

Least Connections

Finally section “Conclusion and future work” concludes our work and points out some future directions. An ADC with load balancing capabilities helps IT departments ensure scalability and availability of services. Its advanced traffic management functionality can help a business steer requests more efficiently to the correct resources for each end user. An ADC offers many other functions that can provide a single point of control for securing, managing, and monitoring the many applications and services across environments and ensuring the best end-user experience.

The RQ4 tries to answer time complexity of the algorithm being used in load balancing process and should be considered as a benchmark to determine performance of a load balancing algorithm. However, as a matter of concern we could not find enough literature determining the algorithmic complexity of an approach being used in the process. Out of top 35 studies conducted in this research only 7 studies considers the algorithmic complexity in their work which accounts to only 20% and the figure may drop as we increase the search space. For example, each client must be able to send and receive data over the course of a session. The simplest is round-robin, where incoming requests are distributed in turn to each resource. Or, the LB can choose the optimal destination, where the definition of “optimal” can be based on several possible criteria (e.g., the smallest current workload, the least latency, the fewest active connections, etc.).

  • Further on the basis of mode of execution of tasks, dynamic algorithms are grouped as offline mode also called as batch mode and online mode or live mode as shown in Fig.3.
  • Virtual — Virtual load balancing aims to mimic software-driven infrastructure through virtualization.
  • Load balancing has a variety of applications from network switches to database servers.
  • Finally Table4 presents the essential load balancing metrics analyzed in the existing approaches.
  • Load balancing is the process by which network or application traffic is distributed across multiple servers in a server farm or server pool.

From DNS requests to web servers, load balancing can mean the difference between costly downtime and a seamless end user experience. Further, from the study carried out in this work, it is investigated that majority of the works primarily focus on certain metrics and avoids other main metrics. Considering these metrics in future works is also one of the insights for future researchers.

What Are Some Of The Common Load Balancing Algorithms?

Even a full server failure won’t impact the end user experience as the load balancer will simply route around it to a healthy server. A frontend server receives the request and determines where to forward it. Various algorithms can be used to determine where to forward a request, with some of the more basic algorithms including random choice or round robin. If there are no available backend servers, then the frontend server performs a predetermined action such as returning an error message to the user. Two of the most critical requirements for any online service provider are availability and redundancy.

How Load Balancing Works

The time it takes for a server to respond to a request varies by its current capacity. If even a single component fails or is overwhelmed by requests, the server is overloaded and both the customer and the business suffer. Ensuring optimal end-user experiences on your network through balanced speeds and performance requires a load balancer to manage heavy traffic and application usage.

Layer 7 load balancers act at the application level, the highest in the OSI model. They can evaluate a wider range of data than L4 counterparts, including HTTP headers and SSL session IDs, when deciding how to distribute requests https://globalcloudteam.com/ across the server farm. As concurrent demand for software-as-a-service applications in particular continues to ramp up, reliably delivering them to end users can become a challenge if proper load balancing isn’t in place.

Ability to scale beyond initial capacity by adding more software instances. Global Server Load Balancing extends L4 and L7 load balancing capabilities to servers in different geographic locations. Actionable insights by load balancers that can help drive business decisions. Reduces Development of High-Load Systems the need to implement session-failover, as users are only sent to other servers if one goes offline. To make things worse, sites that become extremely popular have to deal with consistent increases in monthly traffic, which can slow down the experience for everyone involved.

Stateful Vs Stateless Load Balancing

Also majority of existing load balancing approaches have been implemented on simulator platforms which overall constitute 94.44%. Real time implementation of load balancing is very less (5.56) and should be encouraged in future works. On the basis of type, LB algorithms are classified as VM LB, CPU LB, task LB, server LB, network LB and normal cloud LB as shown in Fig.5. VM load balancing identifies over committed nodes and redistributes VMs from those nodes to under committed nodes. VMs are live migrated from a node exceeding threshold to a newly added node in failure cluster. CPU load balancing is the process of limiting the load on a CPU within its threshold limit.

Software load balancers provide predictive analytics that determine traffic bottlenecks before they happen. This allows routing decisions based on attributes like HTTP header, uniform resource identifier, SSL session ID and HTML form data. In the seven-layer Open System Interconnection model, network firewalls are at levels one to three (L1-Physical Wiring, L2-Data Link and L3-Network). Meanwhile, load balancing happens between layers four to seven (L4-Transport, L5-Session, L6-Presentation and L7-Application). Least Connection Method — directs traffic to the server with the fewest active connections. Most useful when there are a large number of persistent connections in the traffic unevenly distributed between the servers.

How Load Balancing Works

A DNS load balancer distributes traffic to several different IP addresses, whereas the hardware solution uses a single IP address and splits traffic leading to it on multiple servers. As for pricing, hardware load balancers require a large upfront cost whereas DNS load balancers can be scaled as needed. In a cloud environment with multiple web services, load balancing is essential. By distributing network traffic and information flows across multiple servers, a load balancer ensures no single server bears too much demand.

Global Server Load Balancing

The advantages and limitations of existing methods are highlighted with crucial challenges being addressed so as to develop efficient load balancing algorithms in future. The paper also suggests new insights towards load balancing in cloud computing. An application load balancer is one of the features of elastic load balancing and allows simpler configuration for developers to route incoming end-user traffic to applications based in the public cloud. In addition to load balancing’s essential functionality, it also ensures no single server bears too much demand. As a result, it enhances user experiences, improves application responsiveness and availability, and provides protection from distributed denial-of-service attacks.

The multi- criteria optimization is further classified as multi-attribute and multi-objective optimization. The multi- objective algorithms may be either machine learning based, nature inspired based, swarm based or mathematical derived based load balancing algorithms. Figure6 shows the load balancing algorithms on the basis of technique used. Load balancing helps businesses detect server outages and bypass them by distributing resources to unaffected servers. This allows you to manage servers efficiently, especially if they are distributed across multiple data centres and cloud providers.

How Load Balancing Works

Load balancers help solve the performance, economy, and availability problems. Aload balanceris also called the “traffic cop” because it monitors your servers and routes client requests across all servers capable of fulfilling those requests. They work to maximize speed, capacity utilization, and ensures that no one server is overworked, which could degrade performance. Load balancing technologies are needed to redirect traffic to available online servers if there are other servers that are down. Load balancing is needed in any high traffic site but to understand what load balancing is, we first have to take a look at a network system.

Activities Involved In Load Balancing

Network load balancing relies on layer 4 and takes advantage of network layer information to determine where to send network traffic. Network load balancing is the fastest load balancing solution, but it lacks in balancing the distribution of traffic across servers. A hardware-based load balancer is dedicated hardware with proprietary software installed. It can process large amounts of traffic from various application types.

Since one client can create a log of requests that will be sent to one server, hashing on source IP will generally not provide a good distribution. However, a combination of IP and port can create a hash value as a client creates individual requests using a different source pot. Elastic — Elastic Load Balancing scales traffic to an application as demand changes over time. TCP load balancing provides a reliable and error-checked stream of packets to IP addresses, which can otherwise easily be lost or corrupted.

Meanwhile, Milani et al. reviewed existing load balancing techniques, established on the survey; authors grouped existing algorithms into three broad domains as static, dynamic and hybrid. The authors formalized relevant questions towards load balancing and addressed key concern about importance, expectation level of metrics, role and challenges faced in load balancing. This gap in metric selection for analysis is overcome in this survey. In this section load balancing algorithms are classified based on various criteria. A top down approach is proposed and followed in classification process.

Reasonably simple to implement for experienced network administrators. Loads are broken up based on a set of predefined metrics, such as by geographical location, or by the number of concurrent site visitors. Load balancing can be performed at various layers in the Open Systems Interconnection Reference Model for networking.

To manage traffic at Facebook scale, we have deployed a globally distributed network of points of presence to act as proxies for our data centers. Section “Load balancing model background” features a brief description about load balancing model in cloud computing. The research methodology is discussed in section “Research methodology”. Section “Proposed classification of load balancing algorithms” proposes taxonomy based classification. The results are evaluated in section “Results and discussion” while section “Discussion on open issues on load balancing in cloud computing” discusses upon open issues in cloud load balancing.

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