nats-connector

An OpenFaaS event-connector to trigger functions from NATS Core pub/sub topics.

Is the nats-connector or JetStream for OpenFaaS right for you?

At most once QoS: Core NATS offers an at most once quality of service. If a subscriber is not listening on the subject (no subject match), or is not active when the message is sent, the message is not received. This is the same level of guarantee that TCP/IP provides. Core NATS is a fire-and-forget messaging system. It will only hold messages in memory and will never write messages directly to disk.

From the NATS docs

If no nats-connector is available at the time of a message being published, it will not be delivered to any functions. Likewise, if the function is unavailable or crashing, it will not receive the message. NATS Core has no durability.

For production and commercial use, see: JetStream for OpenFaaS

Quick start

Deploy the connector to faasd

See the eBook Serverless For Everyone Else for instructions and sample YAML to add to your faasd host.

Or deploy the connector to Kubernetes

1. Deploy the connector using arkade

   arkade install nats-connector

   Alternatively, see the Helm chart

2. Deploy the two test functions

   git clone https://github.com/openfaas/nats-connector --depth=1
   cd nats-connector/contrib/test-functions

   Deploy the functions using stack.yml, see how the receive-message function has the topic=nats-test annotation? That's how a function binds itself to a particular NATS Subject.

   faas-cli template pull stack
   faas-cli deploy

3. Now publish a message on the nats-test topic.

   Invoke the publisher

   faas-cli invoke publish-message <<< "test message"

4. Verify that the receiver was invoked by checking the logs

   faas-cli logs receive-message
   
   2019-12-29T19:06:50Z 2019/12/29 19:06:50 received "test message"

Configuration

Configuration of the binary is by environment variable. The names vary for the values.yaml file in the Helm chart.

Variable	Description	Default
topics	Delimited list of topics	nats-test,
broker_host	The host, but not the port for NATS	nats
async_invocation	Queue the invocation with the built-in OpenFaaS queue-worker and return immediately	false
gateway_url	The URL for the OpenFaaS gateway	http://gateway:8080
upstream_timeout	Timeout to wait for synchronous invocations	60s
rebuild_interval	Interval at which to rebuild the map of topics <> functions	5s
topic_delimiter	Used to separate items in topics variable	,