Print some instructions and information (#2)

These instructions include what the local address is, which endpoints there are, and how to use this with am.

It is also possible to change the listen address by exporting the LISTEN_ADDRESS environment variable, which defaults to 127.0.0.1:3000.

Author: hatchan

README.md

@@ -37,6 +37,10 @@ cargo run
 
 The application will start on a port 3000 by default and expose a metrics endpoint.
 
+NOTE: You can override the listen address by exporting the `LISTEN_ADDRESS`
+environment variable. Note that you have to use this same address in the next
+step.
+
 4. Start the Autometrics CLI and Explorer
 
 Start the Autometrics CLI and point it to the endpoint it can scrape metrics from.

src/main.rs

@@ -2,6 +2,7 @@ use axum::http::StatusCode;
 use axum::response::IntoResponse;
 use axum::routing::get;
 use axum::Router;
+use std::env;
 use std::time::Duration;
 use tokio::time::sleep;
 
@@ -20,7 +21,7 @@ const API_SLO: Objective = Objective::new("api")
     .latency(ObjectiveLatency::Ms250, ObjectivePercentile::P90);
 
 #[tokio::main]
-async fn main() {
+async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
     // Set up the exporter to collect metrics
     prometheus_exporter::init();
 
@@ -33,11 +34,29 @@ async fn main() {
             get(|| async { prometheus_exporter::encode_http_response() }),
         );
 
-    let addr = "[::]:3000".parse().unwrap();
-    axum::Server::bind(&addr)
-        .serve(app.into_make_service())
-        .await
-        .unwrap();
+    let addr = env::var("LISTEN_ADDRESS")
+        .unwrap_or_else(|_| "127.0.0.1:3000".to_string())
+        .parse()?;
+
+    let server = axum::Server::try_bind(&addr)?.serve(app.into_make_service());
+
+    let local_addr = server.local_addr();
+
+    eprintln!("Listening on: {local_addr}",);
+    eprintln!("");
+    eprintln!("The following endpoints are available: ");
+    eprintln!("");
+    eprintln!("- http://{local_addr}/        | static 200 response",);
+    eprintln!("- http://{local_addr}/slow    | same but it is delayed with 1 second",);
+    eprintln!("- http://{local_addr}/error   | static 500 response",);
+    eprintln!("- http://{local_addr}/metrics | Prometheus endpoint containing the metrics",);
+    eprintln!("");
+    eprintln!("To see the metrics in Explorer run: `am start {local_addr}`");
+
+    // Start accepting and handling requests
+    server.await?;
+
+    Ok(())
 }
 
 // our main handler function that is fine