Solving Four Kubernetes Networking Challenges

One of the main responsibilities of Kubernetes is to share nodes between applications. Networking is a prerequisite because these applications need to communicate with each other and with the outside world.

Architecture of distributed applications hosted by Kubernetes

Typically, requests from outside the Kubernetes cluster pass through a router or API gateway that is responsible for passing them on to the appropriate services. The responsibility of Kubernetes networks is to provide the underlying communication layer, allowing requests to reach their intended destinations.

Distributed applications have spread across many nodes. When there are multiple replicas of each application, Kubernetes handles service discovery and communication between the service and Pods. Inside the capsule, the containers can communicate easily and transparently. Within the cluster, Pods can communicate with other Pods, which is made possible through a combination of virtual network interfaces, bridges, and routing rules through an overlay network.

Despite the transparent handling, Kubernetes networks are more complex than they seem. Deploying across multiple clouds, maintaining multiple environments, and ensuring reliable and scalable network policies are major challenges. Not all of these complexities were originally addressed by Kubernetes. In this article, we’ll look at how to tackle these challenges.

Kubernetes Networking Basics

In Kubernetes, Pods are responsible for handling connections from one container to another. Pods make use of network namespaces through their network resources (interfaces and routing tables). Within the Pod, containers share these resources, allowing them to communicate via localhost.

Pod-to-Pod connections must meet the following Kubernetes requirements:

  • Pods need to communicate without Network Address Translation (NAT).
  • Nodes must be able to communicate with pods without NAT.
  • The IP address that a Pod assigned to itself can see must match the IP that other Pods see.

The Container Network Interface (CNI) includes a specification for writing network plug-ins to configure network interfaces. This allows you to create overlay networks that meet the requirements of a Pod-to-Pod connection.

The service is a Kubernetes abstraction that allows Pods to detect and receive requests. Provides service discovery mechanism through Pod labels and basic load balancing capabilities. Apps running inside Pods can easily use services to connect to other apps running in the group. Requests from outside the group can be routed through access controllers. These controllers will use access resources to configure routing rules, and typically make use of services to facilitate routing to the correct applications.

Non-trivial challenges

While these network capabilities provide the building blocks for workloads managed by Kubernetes, the dynamic and complex nature of cloud-native systems presents many challenges.

Reliability of service-to-service communications

In distributed systems, business functions are broken down into multiple independent services that operate across a set of nodes, pods, and containers. Microservices architecture introduces the need for services to communicate over a network.

The volatile and resilient nature of the cloud requires continuous monitoring of the Kubernetes cluster and redirection in the event of failure. With ephemeral pods and constant redirection of resources, reliable service-to-service communication is never a given.

Effective load balancing algorithms need to map traffic to available replicas and isolate those that are overloaded. Likewise, a service failure means that client requests need to be retried and gracefully timed out. Complex scenarios may need circuit breakers and load separation techniques to handle increases in demand and failures.

Detailing multi-cloud deployments

Complex and large-scale systems are often divided into multiple environments, with different parts deployed on different cloud platforms. These heterogeneous environments need to communicate with each other.

Even within the same cloud lease – or on-premises – the same workload can run in different environments (development, staging, production). Although these environments are separated, sometimes they need to communicate with each other. For example, a staging environment may need to simulate a production workload and rigorously test the application before it goes live. With successful testing, both code and data may need to be migrated from.

Smooth migration can be challenging in such cases. Also, there may be cases where the team simultaneously supports both VM and Kubernetes hosted services. Or, perhaps a team designs systems that support multi-cloud – or at least multi-zone – deployments for reliability, defining complex network configurations and establishing entry and exit rules.

service discovery

When Kubernetes runs in cloud-native environments, it is easy to scale services by producing multiple replicas across multiple nodes. These application replicas are ephemeral – they are instantiated and destroyed as Kubernetes deems necessary. It is not easy for the microservices in the application to keep track of all these changes to IP addresses and ports. However, these microservices need an efficient way to find service replicas.

Network rule scalability

Security best practices and industry regulations such as the Payment Card Industry Data Security Standard (PCI DSS) enforce strict network rules. These rules impose strict limits on communication between services.

Kubernetes has the concept of network policies. These allow you to control traffic at the IP address or port level. You can define rules that enable Pod to communicate with other services using labels and identifiers.

As your system of microservices grows to hundreds or thousands of services, managing network policy becomes a complex, tedious, and error-prone process.

How can a Kong entry controller help

The Kubernetes Ingress Controller (KIC) from Kong is an Ingress implementation of Kubernetes. Powered by Kong Gateway, this Ingress console acts as a native, unrestricted, and scalable, cloud-native API gateway. It is designed for hybrid and multicloud environments and optimized for small services and distributed architectures.

KIC allows configuration of routing rules, health checks, and load balancing, and it supports a variety of plug-ins that provide advanced functionality. This wide range of capabilities can help meet the challenges we’ve discussed.

Reliable communication between service and service

Kubernetes services provide simple round robin capabilities. One of the primary features of KIC is load balancing between replicas of the same application. It can use algorithms like weighted connections or less connections, or even complex custom applications. These algorithms take advantage of the KIC service history to provide efficient routing.

With KIC, you can easily configure retries when a service is down, reasonable timeouts, forward requests to healthy service instances, or handle errors. You can also implement failure patterns such as circuit breakers and load separations to smooth and throttle traffic.

Simpler deployments for multiple clouds

Multi-environment and heterogeneous infrastructure deployments require complex network policies and routing configurations. The Kong Gateway, which is integrated into KIC, addresses many of these challenges.

Kong Gateway allows the Service to be registered independently of where the Services are posted. With a registered service, you will be able to add tracks, and KIC will be ready for agent requests to serve you. Additionally, while complex systems can sometimes communicate with different protocols (REST vs gRPC), you can easily configure KIC to support multiple protocols.

The plugin system allows you to extend the functionality of KIC to more complex scenarios. The Kong Plugin Hub contains a powerful set of useful and battle-tested plugins, and KIC enables you to develop and use any plugin that suits your needs.

Enhanced Service Discovery

As mentioned, KIC keeps track of available editions by registering its services. With services integrated with KIC, they can self-register and report their availability. This registration can also be done through third party registration services. By utilizing the service history, KIC can assign client requests for appropriate backgrounds at any time.

Scalable network rules

Although enforcing network rules through network policies can be complex, KIC can easily integrate with service network applications such as CNCF’s Kuma or Istio with the Kong Istio Gateway, expanding the capabilities of network policies and ensuring additional security.

With authentication and authorization policies, you will be able to enhance network security in a secure, consistent and automated manner. Moreover, you can use network policies and service network policies together to provide a better security situation.

An additional benefit of service network integration is that it allows deployment patterns such as canary deployments and blue/green deployments. It also enhances the possibility of observation with reliable scales and traces.

conclusion

Kubernetes can handle common networking tasks, making it easier for developers and operators to provide services on board. However, with large and complex cloud-native systems, networking concerns are rarely simple. Organizations want to break down stacks into microservices, but need to address unique concerns such as effective load balancing or fault tolerance. Likewise, enabling migrations and smooth service transitions between different environments is not easy. The capabilities of the Kubernetes network must be expanded to support a wider range of scenarios.

KIC can efficiently address many of these challenges. It provides a wide range of functions, including advanced routing and load balancing rules, complex entry and exit rules, and fault tolerance procedures. You can greatly improve service discovery with KIC’s service log, which can keep track of all available instances of each service. Easy integration with KIC and service networks can help create robust network security policies and take advantage of different deployment patterns.

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