Chapter 2. About Serverless

2.1. OpenShift Serverless overview

OpenShift Serverless provides Kubernetes native building blocks that enable developers to create and deploy serverless, event-driven applications on OpenShift Container Platform. OpenShift Serverless is based on the open source Knative project, which provides portability and consistency for hybrid and multi-cloud environments by enabling an enterprise-grade serverless platform.


Because OpenShift Serverless releases on a different cadence from OpenShift Container Platform, the OpenShift Serverless documentation does not maintain separate documentation sets for minor versions of the product. The current documentation set applies to all currently supported versions of OpenShift Serverless unless version-specific limitations are called out in a particular topic or for a particular feature.

For additional information about the OpenShift Serverless life cycle and supported platforms, refer to the Platform Life Cycle Policy.

2.1.1. Additional resources

2.2. Knative Serving

Knative Serving supports developers who want to create, deploy, and manage cloud-native applications. It provides a set of objects as Kubernetes custom resource definitions (CRDs) that define and control the behavior of serverless workloads on an OpenShift Container Platform cluster.

Developers use these CRDs to create custom resource (CR) instances that can be used as building blocks to address complex use cases. For example:

  • Rapidly deploying serverless containers.
  • Automatically scaling pods.

2.2.1. Knative Serving resources

The CRD automatically manages the life cycle of your workload to ensure that the application is deployed and reachable through the network. It creates a route, a configuration, and a new revision for each change to a user created service, or custom resource. Most developer interactions in Knative are carried out by modifying services.
The CRD is a point-in-time snapshot of the code and configuration for each modification made to the workload. Revisions are immutable objects and can be retained for as long as necessary.
The CRD maps a network endpoint to one or more revisions. You can manage the traffic in several ways, including fractional traffic and named routes.
The CRD maintains the desired state for your deployment. It provides a clean separation between code and configuration. Modifying a configuration creates a new revision.

2.3. Knative Eventing

Knative Eventing on OpenShift Container Platform enables developers to use an event-driven architecture with serverless applications. An event-driven architecture is based on the concept of decoupled relationships between event producers and event consumers.

Event producers create events, and event sinks, or consumers, receive events. Knative Eventing uses standard HTTP POST requests to send and receive events between event producers and sinks. These events conform to the CloudEvents specifications, which enables creating, parsing, sending, and receiving events in any programming language.

Knative Eventing supports the following use cases:

Publish an event without creating a consumer
You can send events to a broker as an HTTP POST, and use binding to decouple the destination configuration from your application that produces events.
Consume an event without creating a publisher
You can use a trigger to consume events from a broker based on event attributes. The application receives events as an HTTP POST.

To enable delivery to multiple types of sinks, Knative Eventing defines the following generic interfaces that can be implemented by multiple Kubernetes resources:

Addressable resources
Able to receive and acknowledge an event delivered over HTTP to an address defined in the status.address.url field of the event. The Kubernetes Service resource also satisfies the addressable interface.
Callable resources
Able to receive an event delivered over HTTP and transform it, returning 0 or 1 new events in the HTTP response payload. These returned events may be further processed in the same way that events from an external event source are processed.

2.3.1. Using Knative Kafka

Knative Kafka provides integration options for you to use supported versions of the Apache Kafka message streaming platform with OpenShift Serverless. Kafka provides options for event source, channel, broker, and event sink capabilities.


Knative Kafka is not currently supported for IBM Z and IBM Power.

Knative Kafka provides additional options, such as:

  • Kafka source
  • Kafka channel
  • Kafka broker
  • Kafka sink

2.3.2. Additional resources

2.4. About OpenShift Serverless Functions

OpenShift Serverless Functions enables developers to create and deploy stateless, event-driven functions as a Knative service on OpenShift Container Platform. The kn func CLI is provided as a plugin for the Knative kn CLI. You can use the kn func CLI to create, build, and deploy the container image as a Knative service on the cluster.

2.4.1. Included runtimes

OpenShift Serverless Functions provides templates that can be used to create basic functions for the following runtimes:

2.4.2. Next steps