As the worlds of DevOps and NetOps collide and container environments subsume definitions traditionally used in the network, it seems prudent to explore the use of the often-confusing term "ingress" in terms of the data path and container environments.
Ingress and egress as terms have classically been used to describe the direction of traffic on the network from the perspective of the data center. Ingress is inbound, egress is outbound.
As container environments have matured, the term ingress has been applied to have a very specific, application focused definition.
Ingress. An API object that manages external access to the services in a cluster, typically HTTP. Ingress can provide load balancing, SSL termination and name-based virtual hosting.
It is important to pause and note that an ingress resource as defined in a Kubernetes environment describes capabilities assumed to execute within the container perimeter itself.
Each ingress is a reverse proxy that accepts external requests and, based on the rules specified by the Kubernetes ingress resource, directs those requests to the correct Kubernetes service. The service in turn load balances requests across a set of associated containers, usually by way of native layer 4 (TCP) load balancing algorithms. This is one of the ways a unified API is presented to the outside world. The ingress parses the API calls (the URI path) and distributes them to the appropriate container-hosted microservices inside the container cluster.
F5 provides the same capabilities as a classical Kubernetes ingress but adds additional capabilities in the form of SNI routing and layer 4 (TCP) load balancing. The ability to perform SNI (server name indicator) routing is a benefit for those desiring end-to-end TLS encryption of message exchanges, as it enables F5 to properly route requests based on information in the headers without decrypting the actual payload/message. While this restricts the range of functionality that can be applied to the request – for example, it cannot be scanned for malicious content – it provides the necessary support for architectures in which content must remain encrypted for regulatory or operational reasons. Layer 4 (TCP) load balancing is often used external to a container environment to scale Kubernetes style ingress services.
F5 is typically deployed external to the container environment. It's often used as a load balancing solution to expose clusters externally, i.e. provide public access to services comprised of a container cluster. A CNCF survey found that 67% of respondents choose a load balancer option to expose cluster services externally, with another 33% leveraging ingress (L7) capabilities.
In order for us to provide the same capabilities as a Kubernetes ingress, a container-native "connector" is used to facilitate updates to the policies that define traffic policies. This connector resides inside and integrates with the container orchestrator (typically Kubernetes but Red Hat OpenShift is also popular). Communication with F5 ingress is accomplished via API. Updates include changes to ingress resource definitions (HTTP routing policies) as well as changes to configuration such as the launch or removal of a container instance that impacts a current service definition.
The advantage of using F5 over simple ingress services is the ability to apply advanced capabilities to inbound and outbound traffic. Security, header enrichment, and client-specific performance optimizations can be applied when using F5 without modifying the container environment or architecture or the application itself.