ce-go-template

README

Ce-go-template

Ce-go-template is a collection of services which process a CloudEvent with a go template. As the go-template includes the sprig functions you can use built-in functionality for collections, strings, math, security/encryption, etc. A main purpose is to use the services for building knative eventing primitives. We can group the services according to their role in an event processing chain:

Group	Knative eventing primitives
producers	ContainerSource,Sinkbinding
mappers	Sequence,Parallel,Sinkbinding
filters	Parallel

producers

@startuml
InputSource -> EventProducer: input
hnote over EventProducer : go-template transformation
EventProducer -> EventSink: cloud event
@enduml

Go-Template transforms an input data structure to a cloudEvent and sends them to an event sink. In knative a producer can be applied as an event source using a ContainerSource or a Sinkbinding

producer name	Input	Description
periodic-producer	void	Sends events frequently based on a configurable time period. See details
http-server-producer	HTTP-Request	Sends events based on an incoming http request. See details

mappers

A mapper transforms an incoming CloudEvent to an outgoing CloudEvent. Depending whether an event sink is present, the new event is either sent to the sink ( send mode), or is the payload of the http response (reply mode)

@startuml
EventSource -> EventMapper: cloud event
hnote over EventMapper : go-template transformation
EventMapper --> EventSource: transformed cloud event in respoonse
note right: if no `K_SINK`
EventMapper -> EventSink: transformed cloud event
note left: if `K_SINK` defined
@enduml

mapper name	Description
ce-go-template-mapper	Transforms events based on a go-template. See details
ce-go-template-http-client-mapper	Transforms an event to HTTP-Request and sends it to a HTTP server. The response is transformed to the outgoing cloud event. See details

filters

A filter replies with the incoming CloudEvent, if a predicate string built by a go-template resolves to "true". Otherwise the response has no content. In knative a filter can be applied in Flows like Parallel

@startuml
EventSource -> EventFilter: cloud event
hnote over EventFilter : go-template transformation
EventFilter --> EventSource:  cloud event in response
note right: if transformation is "true"

EventFilter --> EventSource:  no content in response
note right: if transformation is not "true"

@enduml

filter name	Description
ce-go-template-filter	Transforms events to a predicate string based on a go-template. See details
ce-go-template-http-client-filter	Transforms an event to HTTP-Request and sends it to a HTTP server. The response is transformed to the outgoing cloud event. See details

deployment options in knative

event producer as container source

# create event display
kn service create event-display --image gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display --cluster-local --scale-min 1
# create event source
kubectl apply -f deployments/producer-display-eventsource.yaml

event producer with sinkbinding

# create event display
kn service create event-display --image gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display --cluster-local --scale-min 1
# create the sink binding
kubectl apply -f deployments/producer-display-sinkbinding.yaml
# create producer service
kubectl create deployment event-producer --image=docker.io/alitari/ce-go-template-periodic-producer

event mapper in sequence

# create event display
kn service create event-display --image gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display --cluster-local --scale-min 1
# create event mapper in reply mode
kn service create event-mapper --image=docker.io/alitari/ce-go-template-mapper --cluster-local --scale-min 1
# create sequence
kubectl apply -f deployments/sequence.yaml
# create pingsource
kubectl apply -f deployments/pingsource-sequence.yaml

event mapper as subject

# create event display
kn service create event-display --image gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display --cluster-local --scale-min 1
# create the sink binding
kubectl apply -f deployments/mapper-display-sinkbinding.yaml
# create event mapper in send mode
kn service create event-mapper --image=docker.io/alitari/ce-go-template-mapper --scale-min 1
# make a request
MAPPER_URL=$(kubectl get ksvc event-mapper -o=json | jq -r .status.url)
http POST $MAPPER_URL "content-type: application/json" "ce-specversion: 1.0" "ce-source: http-command" "ce-type: http.demo" "ce-id: 123-abc" name=Hase