why we need load balancer in front of api gateway
Relying on API gateway like kong, apigee as a single entry point to your application introduces a potential single point of failure. If the API gateway goes down, it can indeed prevent access to your entire application, affecting availability and reliability. However, there are strategies and best practices to mitigate this risk and ensure high availability and resilience.
1. High Availability Setup
Deploying Kong in a high availability (HA) configuration is crucial. This usually means running multiple instances of Kong across different servers or data centers. These instances can share the load, and if one instance fails, the others can continue to handle API requests without interruption.
2. Load Balancing
A load balancer sits in front of your Kong instances to distribute incoming traffic evenly across them. This not only helps in efficiently utilizing resources but also ensures that if one Kong instance goes down, the load balancer can redirect traffic to the remaining healthy instances. Cloud providers offer managed load balancers that can be configured to monitor the health of Kong instances and automatically reroute traffic as needed.
3. Auto-Scaling
Auto-scaling ensures that the number of Kong instances can dynamically increase or decrease based on the traffic load. This capability helps handle sudden spikes in traffic and improves the resilience of the system by automatically replacing failed instances with new ones.
4. Active Monitoring and Alerting
Continuous monitoring of Kong's health and performance metrics is essential. Monitoring tools and services can help detect anomalies or failures early and trigger alerts. In some cases, automated responses, such as spinning up new instances or restarting failed services, can be initiated in response to these alerts.
5. Disaster Recovery Planning
A comprehensive disaster recovery plan should include strategies for backing up and restoring Kong's configuration and data. In the event of a major failure, being able to quickly restore Kong's state to a new environment or data center can be critical for minimizing downtime.
6. Decoupling Services
While not specific to Kong, designing your microservices architecture to degrade gracefully in the event of certain failures can help maintain partial functionality even if the API gateway layer is experiencing issues. This might mean having fallbacks or cached responses in client applications.
Example Scenario
Imagine you have Kong deployed in an HA configuration across three different servers in different availability zones. A load balancer distributes incoming traffic among these Kong instances. Suddenly, one instance fails due to a hardware issue. The load balancer detects this failure and stops sending traffic to the failed instance, redirecting it to the remaining healthy instances instead. Behind the scenes, an auto-scaling group detects the reduction in capacity and launches a new Kong instance to replace the failed one. Monitoring tools send alerts about the incident to the operations team, but the overall impact on the application is minimal as the system continues to operate normally.
By implementing these strategies, you can significantly reduce the risks associated with relying on API gateway as a critical component of your infrastructure.