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Load Balancer

Categories​

Layer 4 (L4) Load Balancer​

  • A.K.A Network Load Balancing
  • Happens on Transport Layer
  • Decision will be based on the TCP or UDP ports that packets use along with their source and destination IP addresses.
  • Performs Network Address Translation (NAT) on the request packet.
  • Maximizes the utilization and availability by distributing the traffic across IP addresses, switches, and routers.

Layer 7 (L7) Load Balancer​

  • A.K.A Application Load Balancer / HTTP(S) Load Balancer
  • Happens on Application Layer
  • Uses information such as HTTP header, cookies, uniform resource identifier, SSL session ID, and HTML form data to decide the routing request across the servers.

Global Server Load Balancing (GSLB)​

  • Distribute across servers globally
  • DNS load balancing / CDN caching

Static Algorithms​

Round Robin​

  • Distributed across the servers in a sequential or rotational manner
  • Doesn’t consider the load already on a server so there is a risk that one of the servers receives a lot of requests and becomes overloaded

Weighted Round Robin​

  • Similar to round robin, plus each of the resources in a list is provided a weighted score
  • Some of the servers get a bigger share of the overall request.

Source IP Hash​

  • Request is sent to the server based on the client’s IP address.

URL Hash​

  • Request is sent to the server based on the client’s URL.
  • Cache the hash value and subsequent requests will map to the same server.

Randomized algorithm​

  • Maps requests to a random destination.
  • Works well with server cluster with similar configurations.

Dynamic Algorithms​

Least Connection​

  • Request will be directed to the server with the fewest number of requests or active connections.
  • Load balancer needs to do some additional computing to identify the server with the least number of connections.
  • Most useful when there is a huge number of persistent connections in the traffic unevenly distributed between the servers.

Weighted Least Connection​

  • Request will be directed to the server with the fewest number of requests or active connections and relative capacity of server.
  • Server are weighted based on processing capabilities

Least Response Time​

  • Request is forwarded to the server with the fewest active connections and the least average response time.