# Hello World - Rust
A simple web app written in Rust that you can use for testing. It reads in an
env variable `TARGET` and prints "Hello \${TARGET}!". If
TARGET is not specified, it will use "World" as the TARGET.
## Prerequisites
- A Kubernetes cluster with Knative installed and DNS configured. Follow the
[Knative installation instructions](https://knative.dev/docs/install/) if you need to create
one.
- [Docker](https://www.docker.com) installed and running on your local machine,
and a Docker Hub account configured (we'll use it for a container registry).
## Steps to recreate the sample code
While you can clone all of the code from this directory, hello world apps are
generally more useful if you build them step-by-step. The following instructions
recreate the source files from this folder.
1. Create a new file named `Cargo.toml` and paste the following code:
```toml
[package]
name = "hellorust"
version = "0.0.0"
edition = "2018"
publish = false
[dependencies]
hyper = { version = "0.14.7", features = ["full"]}
tokio = { version = "1.5.0", features = ["macros", "rt-multi-thread"] }
pretty_env_logger = "0.4.0"
```
1. Create a `src` folder, then create a new file named `main.rs` in that folder
and paste the following code. This code creates a basic web server which
listens on port 8080:
```rust
use hyper::{
server::conn::AddrStream,
service::{make_service_fn, service_fn},
Body, Request, Response, Server,
};
use std::convert::Infallible;
use std::env;
#[tokio::main]
async fn main() {
pretty_env_logger::init();
let mut port: u16 = 8080;
match env::var("PORT") {
Ok(p) => {
match p.parse::<u16>() {
Ok(n) => {
port = n;
}
Err(_e) => {}
};
}
Err(_e) => {}
};
let addr = ([0, 0, 0, 0], port).into();
let make_svc = make_service_fn(|_socket: &AddrStream| async move {
Ok::<_, Infallible>(service_fn(move |_: Request<Body>| async move {
let mut hello = "Hello ".to_string();
match env::var("TARGET") {
Ok(target) => {
hello.push_str(&target);
}
Err(_e) => hello.push_str("World"),
};
Ok::<_, Infallible>(Response::new(Body::from(hello)))
}))
});
let server = Server::bind(&addr).serve(make_svc);
println!("Listening on http://{}", addr);
if let Err(e) = server.await {
eprintln!("server error: {}", e);
}
}
```
1. In your project directory, create a file named `Dockerfile` and copy the code
block below into it.
```docker
# Use the official Rust image.
# https://hub.docker.com/_/rust
FROM rust:1.51.0
# Copy local code to the container image.
WORKDIR /usr/src/app
COPY . .
# Install production dependencies and build a release artifact.
RUN cargo install --path .
# Run the web service on container startup.
CMD ["hellorust"]
```
1. Create a new file, `service.yaml` and copy the following service definition
into the file. Make sure to replace `{username}` with your Docker Hub
username.
```yaml
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
name: helloworld-rust
namespace: default
spec:
template:
spec:
containers:
- image: docker.io/{username}/helloworld-rust
env:
- name: TARGET
value: "Rust Sample v1"
```
## Build and deploy this sample
Once you have recreated the sample code files (or used the files in the sample
folder) you're ready to build and deploy the sample app.
1. Use Docker to build the sample code into a container. To build and push with
Docker Hub, enter these commands replacing `{username}` with your Docker Hub
username:
```bash
# Build the container on your local machine
docker build -t {username}/helloworld-rust .
# Push the container to docker registry
docker push {username}/helloworld-rust
```
1. After the build has completed and the container is pushed to Docker Hub, you
can deploy the app into your cluster. Ensure that the container image value
in `service.yaml` matches the container you built in the previous step. Apply
the configuration using `kubectl`:
```bash
kubectl apply --filename service.yaml
```
1. Now that your service is created, Knative will perform the following steps:
- Create a new immutable revision for this version of the app.
- Network programming to create a route, ingress, service, and load balance
for your app.
- Automatically scale your pods up and down (including to zero active pods).
1. To find the URL for your service, enter:
```bash
kubectl get ksvc helloworld-rust --output=custom-columns=NAME:.metadata.name,URL:.status.url
NAME URL
helloworld-rust http://helloworld-rust.default.1.2.3.4.sslip.io
```
1. Now you can make a request to your app and see the result. Replace
the URL below with the URL returned in the previous command.
```bash
curl http://helloworld-rust.default.1.2.3.4.sslip.io
Hello World!
```
## Removing the sample app deployment
To remove the sample app from your cluster, delete the service record:
```bash
kubectl delete --filename service.yaml
```