Add NATS connector blog

Signed-off-by: Vivek Singh <[email protected]>

_posts/2020-07-08-event-driven-functions-with-openfaas-and-nats.md

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+---
+title: "Event driven functions with OpenFaaS and NATS"
+description: Vivek outlines how you can make use of NATS to trigger your functions in OpenFaaS through the new connector-sdk component.
+date: 2020-07-08
+image: /images/kafka-connector/aluminium-building.jpg
+categories:
+  - NATS
+  - tutorial
+  - examples
+author_staff_member: vivek
+dark_background: true
+---
+
+In this blog post, I will show how you can invoke OpenFaaS function in response to messages sent on NATS topics in publish-subscribe model.
+OpenFaaS functions are accessible over HTTP endpoints via gateway service but OpenFaaS provides several other way to invoke OpenFaaS functions with help of [connector-sdk](https://github.com/openfaas-incubator/connector-sdk). 
+
+* [kafka-connector](https://github.com/openfaas-incubator/kafka-connector) connects OpenFaaS functions to Kafka topics.
+* [nats-connector](https://github.com/openfaas-incubator/nats-connector) an OpenFaaS event-connector to trigger functions from NATS. 
+* [mqtt-connector](https://github.com/openfaas-incubator/mqtt-connector) MQTT connector for OpenFaaS.
+* [cron-connector](https://github.com/openfaas-incubator/cron-connector) triggers OpenFaaS functions based on cron events. 
+* [VMware vCenter connector](https://github.com/openfaas-incubator/openfaas-vcenter-connector) an OpenFaaS event-connector built to consume events from vCenter and to trigger functions.
+
+There are several other connectors which allows you to trigger OpenFaaS functions based on events, are written and managed as a third party project. Please refer to this [link](https://docs.openfaas.com/reference/triggers/) for full list.
+
+## NATS
+
+[NATS](https://nats.io) is a simple, secure and high performance open source messaging system for cloud native applications, IoT messaging, and microservices architectures. In this blog post, I will be using NATS publish-subscribe concept where publishers publishes a message on a topic/subject and subscribers consumes that message by subscribing to that topic/subject.
+
+![NATS Publish Subscribe](/images/2020-openfaas-nats/nats-publish-subscribe.png)
+
+## Pre-requisite Installation
+
+* [k3d](https://github.com/rancher/k3d) to create a [k3s](https://github.com/rancher/k3s) cluster. k3s is lightweight distribution of kubernetes from Rancher Labs.
+* `kubectl` to manage kubernetes cluster.
+* `helm` to install `nats-connector` using helm chart
+* [arkade](https://github.com/alexellis/arkade) to install OpenFaaS. `arkade` is simple CLI tool to install helm charts and apps to your cluster in one command.
+* [faas-cli](https://github.com/openfaas/faas-cli) CLI tool to manage OpenFaaS functions.
+
+> Please make sure you have these tools installed before you proceed next.
+
+## Install Components
+
+#### Create a kubernetes cluster
+
+`k3d` is a tool to run `k3s` in docker. Create a single node `k3s` cluster.
+
+```
+k3d create
+```
+
+Follow instructions returned in the output of this command to configure KUBECONFIG to access the cluster using kubectl.
+
+#### Install OpenFaaS 
+Install OpenFaaS using `arkade`
+
+```
+arkade install openfaas --set basic_auth=true --set functionNamespace=openfaas-fn
+```
+
+Follow instructions printed to obtain the gateway password and login with `faas-cli`
+
+#### Install NATS connector using helm chart
+`nats-connector` is connector which invokes OpenFaaS function when a message is sent to a NATS topic.
+
+```
+helm repo add nats-connector  https://openfaas.github.io/faas-netes
+
+helm install nats-connector openfaas/nats-connector --namespace=openfaas
+
+```
+
+> NATS comes with OpenFaaS installation, so we are not setting up NATS here
+
+#### Login to OpenFaaS gateway using CLI
+
+Port forward the gateway service to access it. 
+
+```
+kubectl port-forward -n openfaas svc/gateway 8080:8080 &
+```
+
+Get the password
+
+```
+PASSWORD=$(kubectl get secret -n openfaas basic-auth -o jsonpath="{.data.basic-auth-password}" | base64 --decode; echo)
+```
+
+Login to the gateway
+
+```
+echo -n $PASSWORD | faas-cli login --username admin --password-stdin
+```
+
+
+## Deploy functions
+`nats-connector` repo comes with test functions to verify installation. It has two OpenFaas functions.
+
+`receive-message` function subscribes to NATS topic nats-test. On every new message on nats-test topic, receive-message will be invoked.
+
+`publish-message` function publishes message to nats-test topic.
+
+Deploy `receive-message` function
+
+```
+faas-cli deploy --name receive-message --image openfaas/receive-message:latest --fprocess='./handler' --annotation topic="nats-test"
+```
+
+Deploy `publish-message` function
+```
+faas-cli deploy --name publish-message  --image openfaas/publish-message:latest  --fprocess='./handler' --env nats_url=nats://nats.openfaas:4222
+```
+
+> Note: You can also build and deploy this function using the stack.yml and code present in nats-connector repository. But for simplicity, I am using pre built and published images of  these functions.
+
+Invoke `publish-message` function to publish a test message
+
+```
+faas-cli invoke publish-message <<< "test message"
+```
+
+When `publish-message` was invoked, it would have pushed `test-message` to the `nats-test` topic on NATS, which would have invoked `receive-message`. We can verify that by checking logs of `receive-message` function.
+
+```
+faas-cli logs receive-message
+
+ARNING! Communication is not secure, please consider using HTTPS. Letsencrypt.org offers free SSL/TLS certificates.
+Handling connection for 8080
+2020-05-29T15:41:17Z 2020/05/29 15:41:17 Started logging stderr from function.
+2020-05-29T15:41:17Z 2020/05/29 15:41:17 Started logging stdout from function.
+2020-05-29T15:41:17Z Forking - ./handler []
+2020-05-29T15:41:17Z 2020/05/29 15:41:17 OperationalMode: http
+2020-05-29T15:41:17Z 2020/05/29 15:41:17 Timeouts: read: 10s, write: 10s hard: 10s.
+2020-05-29T15:41:17Z 2020/05/29 15:41:17 Listening on port: 8080
+2020-05-29T15:41:17Z 2020/05/29 15:41:17 Writing lock-file to: /tmp/.lock
+2020-05-29T15:41:17Z 2020/05/29 15:41:17 Metrics listening on port: 8081
+2020-05-29T15:42:24Z 2020/05/29 15:42:24 stderr: 2020/05/29 15:42:24 received "test message"
+2020-05-29T15:42:24Z 2020/05/29 15:42:24 POST / - 200 OK - ContentLength: 28
+```
+
+### What Next ?
+
+If you are new to OpenFaaS, I would recommend you trying [OpenFaaS workshop](https://github.com/openfaas/workshop) .
+
+If you don't find connector for messaging platform you are using, checkout the [connector-sdk](https://github.com/openfaas-incubator/connector-sdk) which allows you to build event-connectors for OpenFaaS.
+
+If you are looking to contribute to open source project, please join OpenFaaS community [slack channel](https://docs.openfaas.com/community/) and start contributing.