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Triggers

OpenFaaS functions can be triggered easily by any kind of event. The most common use-case is HTTP which acts as a lingua franca between internet-connected systems.

Connectors map one or more topics, subjects or queues from a stateful messaging system or event-source to a number of functions in your cluster.

Can't find the event-source or trigger that you were looking for? Contact us for more info

Cron

Looking to trigger a function on a schedule?

The cron-connector can be used to trigger a function on a schedule, by adding a couple of annotations to your stack.yml file.

Kubernetes also supports a CronJob mechanism, which you can use as an alternative.

See also: Scheduling function runs for more information.

HTTP / webhooks

This is the default, and standard method for interacting with your Functions.

The function URL follows the pattern of:

https://<gateway URL>:<port>/function/<function name>

Async / NATS Streaming

You can execute a function or microservice asynchronously by replacing /function/ with /async-function/ when accessing the endpoint via the OpenFaaS gateway.

The function URL follows the pattern of:

https://<gateway URL>:<port>/async-function/<function name>

You can also pass an X-Callback-Url header with the URL of another endpoint for the response.

More on async: Async Functions

CLI

Trigger a function using the faas-cli by using the function name

echo "triggered" | faas-cli invoke figlet

CLI invocation can also be async by passing the -a flag to the invoke call

Find out more: faas-cli on GitHub

Other Event Sources

Event-connector pattern

The OpenFaaS connector-pattern allows you to create a broker or separate microservice which maps functions to topics and invokes functions via the OpenFaaS Gateway meaning that the OpenFaaS code does not need to be modified per trigger/event-source.

Event-connector pattern

Pictured: Event-connector pattern. One topic, subject or queue can be broadcast to multiple functions.

Add your own event source

If you'd like to add an event source which is not listed below you can fork the OpenFaaS event connector SDK which is written in Go and use this to connect your pub/sub topics or message queues to functions in OpenFaaS.

Apache Kafka (OpenFaaS Pro)

Connect your function(s) to Apache Kafka topics.

See also: Staying on topic: trigger your OpenFaaS functions with Apache Kafka

Request more info

AWS SQS (OpenFaaS Pro)

Trigger your functions from AWS SQS queues.

Request more info

Cron Connector

The cron-connector is an OpenFaaS event-connector which can be used to trigger functions on a timed-basis. It works with all OpenFaaS Providers.

MQTT Connector

The MQTT Connector can be used in conjunction with an MQTT broker such as emitter.io or similar to respond to events from IoT devices and MQTT message producers.

Example usage: Drone tracking project for Packet.com's session CES 2020.

NATS Pub/sub

OpenFaaS has a built-in queue system with NATS Streaming, however you can also invoke functions using the pub/sub mechanism of NATS.

View the nats-connector

Minio / S3

You can trigger OpenFaaS functions using Minio's webhook or Kafka integration.

AWS SNS

AWS SNS subscriptions can be used to trigger OpenFaaS functions. The approach does not require any separate connector. You can subscribe to an SNS topic and confirm the subscription via HTTP.

The AWS SDKs can be used to manage the subscription and to verify messages.

CloudEvents

CloudEvents is a specification for describing event data in a common way.

No connector is required to trigger OpenFaaS functions using CloudEvents.

Follow this example to learn how to trigger functions using the Azure EventGrid and CloudEvents: johnmccabe/cloudevents-slack-demo

RabbitMQ (third-party project)

Invoke functions from RabbitMQ topics. This is a third party project.

More information in the repository: templum/rabbitmq-connector

IFTTT

You can trigger OpenFaaS functions using webhooks sent via the (if this, then that) service.

An example may be triggering a function which forwards Tweets about your brand or project to a given Slack channel. For this combination use the "Twitter search" Applet and have it trigger the "Make a web request" Applet giving the public URL of your OpenFaaS gateway and the receiver function such as https://gw.my-company.com/function/slack-forwarder

See an example of a function built to forward Tweets from IFTTTT to Slack using Golang: filter-tweets.

Visit ifttt.com to learn more.

VMware vCenter

The vcenter-connector by OpenFaaS is an event connector built to consume events from VMware's vCenter product.

With this project your functions can subscribe to events generated by the changes in your vCenter installation - for instance a VM being created, turned on or deleted. By using the connector you can extend the behaviours and functionality of vCenter and create custom workflows for your platform.

Status: if you require support for this project, reach out to us for more info

Link: openfaas-vcenter-connector

Pushbullet (third-party project)

Invoke functions from Pushbullet channels. This is a third party project.

More information in the repository: MrSimonEmms/openfaas-pushbullet-connector