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Creating Knative services
Knative Services are used to deploy an application. Each Knative Service is defined by a Route and a Configuration, which have the same name as the Service, contained in a YAML file. Every time the Configuration is updated, a new Revision is created.
Knative Service Revisions are each backed by a deployment with 2 Kubernetes Services.
For more information about Kubernetes Services, see the Kubernetes documentation.
Before you begin
To create a Knative Service, you will need:
- A Kubernetes cluster with Knative installed.
- Custom domains set up for Knative Services.
Creating a Knative Service
To create an application, you need to create a YAML file that defines a Knative Service. This YAML file specifies metadata about the application, points to the hosted image of the app and allows the Service to be configured.
This guide uses the Hello World sample app in Go to demonstrate the structure of a Service YAML file and the basic workflow for deploying an app. These steps can be adapted for your own application if you have an image of it available on Docker Hub, Google Container Registry, or another container image registry.
The Hello World sample app does the following:
- Reads an environment variable
TARGET
. - Prints
Hello ${TARGET}!
. IfTARGET
is not defined, it will useWorld
as theTARGET
.
Procedure
- Create a new file named
service.yaml
containing the following information.
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
name: helloworld-go
namespace: default
spec:
template:
spec:
containers:
- image: gcr.io/knative-samples/helloworld-go
env:
- name: TARGET
value: "Go Sample v1"
apiVersion
: The current Knative version.name
(metadata): The name of the application.namespace
: The namespace that the application will use.image
: The URL to the image of the application.name
(env): The environment variable printed out by the sample application.
Note: If you’re deploying an image of your own app, update the name of the app and the URL of the image accordingly.
- From the directory where the new
service.yaml
file was created, deploy the application by applying theservice.yaml
file.
kubectl apply --filename service.yaml
Now that your app has been deployed, Knative will perform the following steps:
- Create a new immutable revision for this version of the app.
- Perform network programming to create a route, ingress, service, and load balancer for your app.
- Automatically scale your pods up and down based on traffic, including to zero active pods.
Modifying Knative Services
Any changes to specifications, metadata labels, or metadata annotations for a Service must be copied to the Route and Configuration owned by that Service. The serving.knative.dev/service
label on the Route and Configuration must also be set to the name of the Service. Any additional labels or annotations on the Route and Configuration not specified above must be removed.
The Service updates its status
fields based on the corresponding status
value for the owned Route and Configuration.
The Service must include conditions ofRoutesReady
and ConfigurationsReady
in addition to the generic Ready
condition. Other conditions can also be present.
What’s next?
- For more information about the Knative Service object, see the Resource Types documentation.
- For more information about getting started with deploying a Knative application, see the Getting Started with App Deployment documentation.
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