feat: Health check command (#134)

This PR adds a `health-check` command to the CLI. You can call
`rss-funnel health-check` to check if the server is running and healthy.
The Docker image now also includes the `HEALTHCHECK CMD` directive.

Internally it does a simple GET request to the `/_health` endpoint.

Options:

- `-s`/`--server`/`RSS_FUNNEL_HEALTH_CHECK_SERVER` - The server to
check. Default: `http://127.0.0.1:4080`.

Closes #128.

Dockerfile

@@ -0,0 +1,6 @@
+FROM scratch
+COPY %RELEASE_BINARY% /rss-funnel
+ENTRYPOINT ["/rss-funnel"]
+EXPOSE 8080
+HEALTHCHECK CMD ["/rss-funnel", "health-check"]
+CMD ["server"]

Makefile

@@ -48,8 +48,11 @@ $(IMAGE_NAME)\:latest-% $(IMAGE_NAME)\:nightly-%: $(IMAGE_NAME)\:$(VERSION)-%
 	podman tag $< $@
 
 $(IMAGE_NAME)\:$(VERSION)-%: target/%/release/$(APP_NAME)
-	echo "FROM scratch\nCOPY $< /$(APP_NAME)\nENTRYPOINT [\"/$(APP_NAME)\"]\nCMD [\"server\"]\n" | \
-		podman build -f - . --platform $(PLATFORM_$*) -t $@
+	cat Dockerfile | \
+		sed -e "s|%RELEASE_BINARY%|$<|g" | \
+		podman build -f - . \
+			--format docker \
+			--platform $(PLATFORM_$*) -t $@
 
 # building multiarch manifest requires the image to be pushed to the
 # registry first.

src/cli.rs

@@ -23,11 +23,24 @@ pub struct Cli {
 enum SubCommand {
   /// Start the server
   Server(ServerConfig),
+  HealthCheck(HealthCheckConfig),
   /// Test an endpoint
   // boxed because of the clippy::large_enum_variant warning
   Test(Box<TestConfig>),
 }
 
+#[derive(Parser)]
+struct HealthCheckConfig {
+  /// The endpoint to test
+  #[clap(
+    long,
+    short,
+    default_value = "127.0.0.1:4080",
+    env = "RSS_FUNNEL_HEALTH_CHECK_SERVER"
+  )]
+  server: String,
+}
+
 #[derive(Parser)]
 struct TestConfig {
   /// The endpoint to test
@@ -115,6 +128,9 @@ impl Cli {
         test_endpoint(feed_defn, &test_config).await;
         Ok(())
       }
+      SubCommand::HealthCheck(health_check_config) => {
+        health_check(health_check_config).await
+      }
     }
   }
 }
@@ -144,3 +160,27 @@ async fn test_endpoint(feed_defn: RootConfig, test_config: &TestConfig) {
     println!("{}", feed.serialize(true).expect("failed serializing feed"));
   }
 }
+
+async fn health_check(health_check_config: HealthCheckConfig) -> Result<()> {
+  let mut server = health_check_config.server;
+  if !server.starts_with("http://") && !server.starts_with("https://") {
+    server = format!("http://{server}");
+  }
+
+  let url = Url::parse(&server)?.join("/_health")?;
+  match reqwest::get(url.clone()).await {
+    Ok(res) if res.status().is_success() => {
+      eprintln!("{server} is healthy");
+      Ok(())
+    }
+    Err(e) => {
+      eprintln!("failed to check health: {e}");
+      std::process::exit(1);
+    }
+    Ok(res) => {
+      let status = res.status();
+      eprintln!("{url} returned {status}");
+      std::process::exit(1);
+    }
+  }
+}

src/server.rs

@@ -137,7 +137,9 @@ impl ServerConfig {
       .layer(CompressionLayer::new().gzip(true));
 
     app = app
+      // deprecated, will be removed on 0.2
       .route("/health", get(|| async { "ok" }))
+      .route("/_health", get(|| async { "ok" }))
       .merge(image_proxy::router())
       .merge(feed_service_router)
       .layer(Extension(feed_service));