Load balancing is the process of distributing network traffic across multiple servers. This ensures no single server bears too much demand. By spreading the work evenly, load balancing improves application responsiveness. It also increases availability of applications and websites for users.
Load balancers?manage the flow of information between the server and an endpoint device (PC, laptop, tablet or smartphone). The server could be on-premises, in a?data centre?or the public cloud. The server can also be physical or virtualized. The load balancer helps servers move data efficiently, optimizes the use of?application delivery?resources and prevents server overloads.
In the seven-layer?Open System Interconnection (OSI) model, load balancing happens between layers four to seven (L4-Transport, L5-Session, L6-Presentation and L7-Application).
- Layer 4 load balancing, operating at the transport level, manages traffic based on network information such as application ports and protocols without visibility into the actual content of messages.
- This is an effective approach for simple?packet-level?load balancing. The fact that messages are neither inspected nor decrypted allows them to be forwarded quickly, efficiently, and securely.
- On the other hand, because layer 4 load balancing is unable to make decisions based on content, it’s not possible to route traffic based on media type, localization rules, or other criteria beyond simple algorithms such as round-robin routing.
- Layer 7 load balancing operates at the application level, using protocols such as HTTP and SMTP to make decisions based on the actual content of each message.
- Instead of merely forwarding traffic unread, a layer 7 load balancer terminates network traffic, performs decryption as needed, inspects messages, makes content-based routing decisions, initiates a new TCP connection to the appropriate upstream server, and writes the request to the server.
- While the need for encryption incurs a performance penalty for layer 7 processing, this can be largely reduced through the use of?SSL offload functionality.
- layer 7 load balancing provides the intelligence to handle protocols that piggyback or multiplex requests onto a single connection to optimize traffic and reduce overhead.
- Global Server Load Balancing?extends L4 and L7 capabilities to servers in different geographic locations.
- Global server loading balancing (GSLB)?refers to web traffic management and application delivery over multiple data centres and/or public or private clouds in various geographical areas.
- Passing user requests to the nearest servers minimizes network latency and network issues. GSLB ensures optimal website or service performance to clients in geographically distributed areas.
- Application high availability minimizes the impact of data centre or network failures. For instance, if a power outage affects California, the?load balancer?will redirect client requests to other servers hosted in multiple sites that are spread apart geographically.
- ?If applications are hosted in hybrid clouds, the GSLB system can “burst” to a public cloud to absorb unusually high load.
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