Serverless Rust with Tide, Appsody and Knative

Introduction

This was originally posted in the Appsody Website

This tutorial was created following feedback from the Appsody on OpenShift presentation and will cover how to scaffold, then build a serverless rust application with Appsody and deploy it into a knative environment.

Prerequisites

Install Docker

The instructions for installing docker on your OS are available here.

Install the Appsody CLI

Follow the Installing Appsody guide to install the CLI for your platform.

Create a Knative Environment

Choose one of the options below to create a Knative environment. If you don't have a Knative environment the quickest way to get going is to choose the IBM Cloud option.

You can also use the appsody build in any Knative environment if you already have one with your favourite cloud provider.

Create Your Application

Open a terminal window.
Create a directory named appsodyrusttide:
```
mkdir appsodyrusttide
```
Navigate to that directory:
```
cd appsodyrusttide
```

List the available Appsody stacks with:

appsody list

You should see the rust-tide stack (and template) listed:

REPO            ID                              VERSION         TEMPLATES               DESCRIPTION

...
*experimental      rust-tide                     	0.1.0    	*default                	Tide web framework for Rust 
...

Scaffold a Rust Tide application in the current directory by using the appsody init command as follows:

appsody init experimental/rust-tide

The output should look similar to the following:

Running appsody init...
Downloading rust-tide template project from experimental/rust-tide.v0.1.0.templates.default.tar.gz
Download complete. Extracting files from /home/anton/test/appsodyrusttide/rust-tide.tar.gz
Setting up the development environment
Your Appsody project name has been set to appsodyrusttide
Using local cache for image experimental/appsody/rust-tide:0.1
Running command: docker run --rm --entrypoint /bin/bash experimental/appsody/rust-tide:0.1 -c "find /project -type f -name .appsody-init.sh"
Successfully added your project to /home/anton/.appsody/project.yaml
Your Appsody project ID has been set to 20200601194200.47030643
Successfully initialized Appsody project with the experimental/rust-tide stack and the default template.

The most important lines to make note of are:

Your Appsody project name has been set to `appsodyrusttide`

and

Successfully initialized Appsody project with the rust-tide stack and the default template.

Now open this project in your favorite IDE.
The basic structure of the application looks like this:

rust_tide_appsody_template_files_1.png

One important file is the Appsody configuration file for your project, .appsody-config.yaml:
```
project-name: appsodyrusttide
stack: experimental/rust-tide:0.1
```
It defines the name of your project, and the stack on which it is based.
The source code for the application is located in the src directory.

rust_tide_appsody_template_files_2.png
This basic application only defines one API endpoint '/' in the file src/lib.rs
```
pub fn app() -> tide::Server<()> {    
    let mut api = tide::new();
    api.at("/").get(|_| async move { Ok("Hello, world!") });
    api
}
```
The initial application is very similar to the example application, but it's a library that is loaded by a server at runtime. This helps reduce the cognitive noise for the developer as well as ensuring that best practices are applied in a template format.

Building Your Application

The template application is only a starting point, you will now modify and build this service.

Firstly, you are going to modify the endpoint so it reads an environment variable which is then returned as JSON. This is based on the tide json example but uses an environment variable rather than a POST to demonstrate some of the Knative capabilities.

Update the Cargo.toml to reference serde libraries. This gives our project JSON capaibilities.

[dependencies]
tide = { version = "0.9" }
serde = "1.0.102"
serde_json = "1.0.41"

Now we will update lib.rs to read the environment variable and return a Cat struct to the user.

    use std::env;
    use serde::{Deserialize, Serialize};
    use tide::{Response, StatusCode};

    #[derive(Deserialize, Serialize)]
    struct Cat {
        name: String,
    }

    pub fn app() -> tide::Server<()> {   
        
        let mut api = tide::new();
        api.at("/").get(|_| async move {
            let env_my_name = env::var("MY_NAME").unwrap_or_else(|_| "Not Provided".to_string());
            let cat = Cat {
                name: env_my_name.into(),
            };
            Ok(Response::new(StatusCode::Ok).body_json(&cat)?)
        });
        api
    }

Once the code changes are complete you can run the service with:
```
appsody run --docker-options "--env MY_NAME=tibbs"
```
--docker-options passes the environment settings to the container
The service will be available at http://localhost:8000/ and accessing it in a browser will return:
```
    {
        "name" : "tibbs"
    }
```
Now we need to create a production build for the application. Make sure you are logged into docker hub before running it.
```
$ appsody build -t YOUR_DOCKER_USER/appsodyrusttide:v1.0.0 --publish --knative
```

Deploy Your Application

This section will be split into three sub-sections:

Deploy to Knative on IBM Cloud
Deploy to Minikube
Deploy to Openshift

Deploy to Knative on IBM Cloud

Ensure that you have created a project for the service, then run the following command:

$ ibmcloud coligo application create --name appsodyrusttide --image YOUR_DOCKER_USER/appsodyrusttide:v1.0.0 --env MY_NAME=tibbs

Deploy to Minikube

Create a service definition in the application folder:

apiVersion: serving.knative.dev/v1 # Current version of Knative
kind: Service
metadata:
    name: appsodyrusttide # The name of the app
    namespace: default # The namespace the app will use
spec:
template:
    spec:
    containers:
        - image: docker.io/YOUR_DOCKER_USER/appsodyrusttide:v1.0.0 # The URL to the image of the app
          env:
            - name: MY_NAME # The environment variable printed out by the sample app
              value: "tibbs"

Push the service:
```
$ kubectl apply --filename service.yaml
```
:

Deploy to OpenShift
Deploying to OpenShift is very straight forward and just requires:
```
$ appsody deploy --no-build --knative 
```

Validate Your Application

Get the list of services using the kn cli:

$ kn service list

NAME              URL                                                                     LATEST                     AGE    CONDITIONS   READY   REASON
appsodyrusttide   http://appsodyrusttide.604053c7-2682.us-south.knative.appdomain.cloud   appsodyrusttide-s4lwr5-3   2d7h   3 OK / 3     True

Test the URL returned in the list.

$ curl http://appsodyrusttide.604053c7-2682.us-south.knative.appdomain.cloud 
{
  "name":"tibbs"  
}

Summary

This tutorial was a starter to get a simple service up and running. In the future there will be examples of debugging and connecting to backend systems such as databases.