What is Kubernetes Ingress?

The concept of an Ingress exists outside of Kubernetes and extends to other open source platforms. For the process of implementing an Ingress, a set of rules must be established to assist with influencing incoming traffic. In its most basic essence, it relays an HTTP or HTTPS to a service. These services include routing users to a specific component or pod of a service based on how the link is required to interact with the defined rules. 

An Ingress acts as an entry point for incoming traffic into a system or platform. It provides a way to manage and control the routing of external requests to the appropriate internal services or resources. The Ingress is responsible for analyzing incoming requests based on predefined rules and forwarding them to the correct destination within the system.

The primary purpose of an Ingress is to simplify the management of traffic routing and load balancing for services exposed to the internet or other external networks. It acts as a single point of entry, eliminating the need to configure individual services with their own external IP addresses or load balancers.

Kubernetes itself is an open source platform used to containerize various components like software, applications, and more. These containers are defined as pods, and multiple pods are called a cluster. Using various services or types to define the cluster, the developer can choose how traffic is routed to the cluster or individual pods in specific ways. 

Ingress is a Kubernetes resource that manages external access to services within a cluster. It acts as a single entry point for incoming traffic, routing it to the appropriate services based on the rules the developer sets. Kubernetes Ingress provides a way to securely and efficiently expose services. It eliminates the need for manual management of load balancers or public IP addresses for individual services.

When using ingress to influence how traffic is routed to respective clusters, the developer can define a set of rules to enable specific directions for the incoming traffic. In a cluster, there can be multiple sets of pods that are defined as different services. Using the prior set of rules, specific links used by incoming traffic will send them to a corresponding service.  

The key components of Kubernetes Ingress are:

1. Ingress Controller: This is a specialized load balancer that watches the Ingress resource and processes the rules defined within it. It is responsible for routing incoming traffic to the appropriate services based on the Ingress rules.
2. Ingress Resource: This is a Kubernetes resource that defines the rules for routing incoming traffic. It specifies the hostname, path, and destination services for different types of requests.
3. Ingress Rules: These are the rules defined within the Ingress resource that determine how incoming traffic should be routed. Rules can be based on host, path, or other criteria

The difference between ingress and egress might be simpler than you think. Ingress refers to the traffic coming into a network boundary, while egress refers to the traffic leaving the network boundary. An easy way to remember the distinction is to look at the prefix. Ingress is the traffic coming into, while egress is the traffic exiting. Another easy analogy is the difference between immigration and emigration.

In the context of Kubernetes, Ingress specifically deals with managing incoming traffic from outside the cluster to services within the cluster. It acts as a single entry point, routing external requests to the appropriate services based on predefined rules.

On the other hand, egress in Kubernetes refers to the outgoing traffic from within the cluster to external destinations. It is the mechanism by which services or pods within the cluster can initiate and establish connections to resources outside the cluster, such as databases, APIs, or other external services.

While ingress and egress serve different purposes, they are both essential components for managing traffic flow in a Kubernetes environment. Ingress ensures that external traffic is properly routed and load-balanced across services within the cluster, while egress ensures that services within the cluster can communicate with external resources as needed.

It's important to note that while Ingress is a Kubernetes resource with dedicated controllers and configurations, egress is typically managed through network policies, firewall rules, or other networking configurations within the cluster or the underlying infrastructure.

While both Kubernetes Ingress and a load balancer share similarities, they also have some key distinctions. Both K8s Ingress and a load balancer are responsible for directing traffic to a service, but there is a component where they do differ.

A load balancer is only able to direct toward one service, while K8s Ingress can direct toward multiple services in a cluster. The other main difference is that Kubernetes Ingress natively exists inside the cluster, while a load balancer exists outside.

A load balancer is a standalone component that distributes incoming network traffic across a group of backend servers or services. It acts as a reverse proxy, forwarding client requests to one of the available servers based on a load balancing algorithm. Load balancers are typically used to improve application availability, scalability, and performance by spreading the workload across multiple servers.

While a load balancer can distribute traffic to a single service, Kubernetes Ingress can route traffic to multiple services within the cluster based on predefined rules, such as host, path, or other criteria. This allows for more complex routing scenarios and enables features like name-based virtual hosting and path-based routing.

While both Kubernetes Ingress and a load balancer serve the purpose of managing and distributing incoming traffic, Kubernetes Ingress is a more specialized and integrated solution for managing external access to services within a Kubernetes cluster. It offers advanced routing capabilities, seamless integration with other Kubernetes resources, and additional features tailored for containerized applications running in a Kubernetes environment.

Gateway API is the future of Kubernetes Ingress so they share many similarities in the way they are implemented, but have some distinct differences in their intended application. Kubernetes Ingress works for the HTTP to a cluster, or more specifically, a service within a cluster. While Ingress provides a centralized way to manage external access to services, it has limitations in terms of protocol support (primarily HTTPS), advanced traffic management features, and lack of standardization across different implementations.

The Gateway API project introduces a new set of portable network management resources beyond traditional Kubernetes Ingress capabilities. Gateway API defines a common set of Kubernetes resource objects and usage patterns that all compliant gateways must support, including support for both L4 and L7 protocols, built-in capabilities for advanced traffic management like canary rollouts and request mirroring, and expanded routing customization based on arbitrary headers. Gateway API is more generalized in how it accesses the cluster, and specializes more in having more utility and application with the implementation of API in the HTTP process. It can modify the routing to a Kubernetes cluster in a safe way using a reverse proxy. This addresses the limitations of Ingress and aims to provide a standardized and more feature-rich approach to managing traffic within Kubernetes clusters.

In summary, Kubernetes Ingress provides a centralized and efficient way to manage external access to services running within a Kubernetes cluster. By defining rules for routing incoming traffic based on host, path, or other criteria, Ingress simplifies the process of exposing multiple services through a single entry point. It offers valuable features like load balancing, SSL/TLS termination, name-based virtual hosting, and path-based routing. While sharing some similarities with traditional load balancers, Kubernetes Ingress is specifically designed for Kubernetes environments, enabling advanced traffic management capabilities tailored for containerized applications. As the project continues to evolve, with the introduction of the Gateway API aiming to provide a more standardized and feature-rich approach, Kubernetes Ingress remains an essential component for deploying and managing production-ready applications in Kubernetes clusters.

Continued Learning & Related Content

• Gateway to the Future: A Brief History of Kubernetes Ingress
• Making Kong Cloud-Native with the Kong Ingress Controller
• The Difference Between API Gateways and Kubernetes Ingress
• Enhancing APIOps with decK for Kong Ingress Controller Users
• Gateway API vs Ingress: The Future of Kubernetes Networking
• Managing Docker Apps With Kubernetes Ingress Controller