Web Applications or APIs expose over the network are exposed to a potentially huge network traffic as well as a wide range of security threats. In order to deal with such scenarios, various steps are taken. On the back-end side; scalability is achieved by forming a cluster of servers as per the expected load. With multiple servers offering the same service; load balancing and API management related actions are also required to achieve a sophisticated, scalable, efficient architecture. API Gateway and Load Balancers are the prime choices in this regard. This API Gateway vs Load Balancer article discusses the two concepts in detail and explains the use cases for both.
What is a Load Balancer?
Load Balancer is a software or hardware solution which aims to distribute the load among multiple servers in such a way that client requests are entertained in the best possible manner without overloading any single server. The network load is balanced among multiple servers in a cluster based on some specific balancing algorithm. Load Balancer acts like a traffic cop on a road crossing to direct the cars which path to follow.
Load balancer can be a software or it can be a hardware. In either case, the primary purpose of a load balancer is to achieve better throughput, efficient resource utilization & improve availability. Other than ensuring an efficient distribution of network traffic among multiple servers, load balancers are also equipped with following additional capabilities:
- Most of the load balancers support sticky sessions through session persistence. It ensures that requests from a particular client are always routed to the same backend server, maintaining session state and ensuring a consistent user experience.
- Load balancer also serves the health check functionality. It checks the heart beat of all the servers in a pool and removes any non-responsive servers from the pool temporarily or permanently. This helps achieving fault tolerance as well.
- Load Balancers also provide SSL offloading (also known as SSL Termination) functionality. SSL based HTTPS traffic is subsequently routed towards backend servers without having SSL related extra overhead on the backend servers.
- Content based routing features are also available in load balancers. Such features are available in advanced modern load balancers. Content can be dynamically and smartly routed based on URL, headers or content specific conditions.
Load Balancer Algorithm Types
To balance the load efficiently among the available servers; load balancers can use any of the following algorithms:
- Round Robin: Network traffic is routed evenly among all available servers. Available servers are considered one by one in sequence for the client requests.
- Weighted Round Robin: Servers from the available pool are assigned a weight based on performance and the capacity. Requests are then routed based on the assigned weights–higher the weight, more traffic.
- Least Connections: This algorithm considers number of active connections for the routing of the client requests. Server with the least active connection is given a priority.
- Least Response Time: Using this algorithm, load balancer routes the traffic to the servers based on the response time. Server with the lowest response time is given a priority.
- IP Hash: The IP Hash algorithm uses the client’s IP address to determine which server to send the request to. Hash value is computed from the client’s IP address and used by the load balancer to select a server from the available pool. This ensures that requests from the same IP address are consistently routed to the same server, which can be useful for maintaining session persistence.
- Dynamic Adaptive: This load balancing algorithm makes dynamic intelligent routing decisions based on various key metrics like CPU resources utilization, health check, response time etc. Load is distributed in real time using such decisive factors.
- Random: This is the simplest (and dumbest as well) routing approach where network traffic is randomly distributed among the pool of available servers. The routing decision is made without consideration of any specific factors and hence, this algorithm might not efficiently balance the network traffic.
What is API Gateway?
An API Gateway is a software that acts as a gatekeeper by sitting at the entry points between the clients and the backend services. Various API Management functionalities are provided by an API Gateway. Access to the backend APIs is controlled, managed and governed by the use of API Gateway and its associated API management capabilities.
API Gateway can help achieving better performance by offloading backend servers from plenty of functionalities. Any API calls are intercepted at the entry point and different actions can be performed to segregate, aggregate, manage, control, throttle, enrich and filter the traffic before it is routed to the backend servers.
API Gateways as part of API Management Platforms are equipped with plenty of other features as well. You can configure different types of API Policies like rate limiting, throttling, authentication, authorization, Protocol transformation, data format transformation etc. at the gateway level. Most of the API Gateways also provide necessary security features as explained in this video.
API Gateway vs Load Balancer: What is the Difference Between API Gateway and Load Balancer?
API Gateway and Load balancer both play important role in specific use cases. Now that we have discussed both API Gateway and Load Balancer in detail, the difference between the two can be drawn easily.
Here are some of the major differences between API Gateway and Load Balancer.
- An API Gateway as an entry point provides a wide variety of API management features. On the other hand, Load Balancer’s primarily provide merely the network traffic routing functionality for balancing the load among multiple backend servers.
- An API Gateway is always a software solution while a load balancer can be either a software or a hardware.
- Most of the API Gateways provided by different API Management Platforms are equipped with Load Balancing as well. On the other hand, Load Balancers alone don’t provide any additional API management or governance features exclusively.
- API gateway and Load balancers differ from the context of purpose as well. An API gateway is considered for the use cases where you need to manage entire API Life cycle. On the other hand, Load Balancers are opted where balancing the load is the only major requirement.
- Typically, API Gateway is a preferred choice in Microservices architecture where you have to manage, monitor, govern and control the traffic for a set of APIs. Load balancer alone in such scenarios is not a preferred option.
Does API Gateway Need a Load Balancer?
With API management in place, there is typically no need of a separate software/hardware load balancer. Most of the API gateways are equipped with built-in load balancers. So essentially, API Gateway is itself containing a tiny Load Balancer. API traffic routing to the backend servers from the API gateway happens based on the routing algorithm configurations for each API.
When you configure API Gateway to handle high volumes of traffic or have multiple backend resources, it automatically scales and provisions the necessary resources to handle the load. This eliminates the need for an additional load balancer in front of API Gateway. Built-in load balancer in API Gateway are capable of providing both Load Balancing and Fault Tolerance features.
However, there can be specific use cases where you might still opt for a dedicated network level load balancer on top of API gateway. Different API Management platforms available in the market have different capabilities. There can be cases when you are using some API Management Platform which doesn’t provide enough load balancing capabilities. Having a dedicated Load Balancer can help you filling such a gap efficiently. In this situation, API traffic will be routed by the Load Balancer to the API Gateway Cluster. Subsequently traffic will flow towards the back-end servers.
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