Load balancer
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,
1.
load balancing improves
application responsiveness.
2.
Increases availability of applications
and websites for users.
Modern applications cannot run
without load balancers. Over time, software load balancers have added additional capabilities including application
security.
To utilize full scalability and redundancy, we can try to
balance the load at each layer of the system. We can add LBs at three places:
- Between the user and the web server
- Between web servers and an internal
platform layer, like application servers or cache servers
- Between internal platform layer and database.
What it does?
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 center 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.
Load balancers conduct
continuous health checks on servers to ensure they can handle requests. If
necessary, the load balancer removes unhealthy servers from the pool until they
are restored.
Some load balancers even
trigger the creation of new virtualized application servers to cope with
increased demand.
How does the load balancer choose the backend server?
Load balancers consider two factors before
forwarding a request to a backend server. They will first ensure that the
server they choose is actually responding appropriately to requests and then
use a pre-configured algorithm to select one from the set of healthy servers.
We will discuss these algorithms shortly.
Load Balancing Algorithms
There is a variety of load balancing methods, which use different algorithms best
suited for a particular situation.
- Least Response Time
Method — directs traffic to the server with the fewest active connections
and the lowest average response time.
- Round Robin Method — rotates servers by directing traffic to
the first available server and then moves that server to the bottom of the
queue. Most useful when servers are of equal specification and there are
not many persistent connections.
- IP Hash — the IP address of the client determines which server receives the request.
Benefits of Load Balancing
- Users
experience faster, uninterrupted service.
- Service
providers experience less downtime and higher throughput.
- Makes
system administrators job easy by handing incoming requests while
decreasing wait time for users.
- Smart load balancers provide benefits like predictive analytics that determine traffic bottlenecks before they happen.
References:
https://avinetworks.com/what-is-load-balancing/
https://www.educative.io/courses/grokking-the-system-design-interview/3jEwl04BL7Q
