fix: improve error handling in main

Cargo.toml

@@ -7,7 +7,6 @@ members = [
 resolver = "2"
 
 [workspace.package]
-rust-version  = "1.72.0"
 edition       = "2021"
 authors       = [ "Heiko Seeberger <[email protected]>" ]
 license       = "Apache-2.0"
@@ -27,6 +26,7 @@ opentelemetry-otlp    = { version = "0.12", default-features = false, features =
 prost                 = { version = "0.11" }
 serde                 = { version = "1.0", features = [ "derive" ] }
 serde_json            = { version = "1.0" }
+time                  = { version = "0.3", features = [ "formatting" ] }
 tokio                 = { version = "1", features = [ "macros", "rt-multi-thread", "signal" ] }
 tokio-stream          = { version = "0.1", features = [ "fs" ] }
 tonic                 = { version = "0.9" }

hello-tracing-backend/Dockerfile

@@ -1,4 +1,4 @@
-ARG RUST_VERSION=1.72.1
+ARG RUST_VERSION=1.73.0
 
 FROM rust:${RUST_VERSION}-bullseye AS builder
 RUN apt-get update && \

hello-tracing-backend/src/main.rs

@@ -2,27 +2,42 @@ mod api;
 
 use anyhow::{Context, Result};
 use configured::Configured;
-use hello_tracing_common::tracing::{init_tracing, TracingConfig};
+use hello_tracing_common::{
+    log_error,
+    tracing::{init_tracing, TracingConfig},
+};
 use serde::Deserialize;
+use std::panic;
 use tracing::{error, info};
 
 #[tokio::main]
-async fn main() -> Result<()> {
-    let config = Config::load().context("load configuration")?;
-    init_tracing(config.tracing.clone()).context("initialize tracing")?;
+async fn main() {
+    // Load configuration first, because needed for tracing initialization.
+    let config = match Config::load().context("load configuration") {
+        Ok(config) => config,
+        Err(error) => {
+            log_error(error);
+            return;
+        }
+    };
 
-    info!(?config, "starting");
+    // If tracing initialization fails, nevertheless emit a structured log event.
+    if let Err(error) = init_tracing(config.tracing.clone()) {
+        log_error(error);
+        return;
+    }
 
-    let result = api::serve(config.api).await;
+    // Replace the default panic hook with one that uses structured logging at ERROR level.
+    panic::set_hook(Box::new(|panic| error!(%panic, "process panicked")));
 
-    if let Err(error) = result {
+    // Run and log any error.
+    if let Err(error) = run(config).await {
         error!(
             error = format!("{error:#}"),
             backtrace = %error.backtrace(),
-            "hello-tracing-backend exited with ERROR"
+            "process exited with ERROR"
         );
     };
-    Ok(())
 }
 
 #[derive(Debug, Deserialize)]
@@ -31,3 +46,9 @@ struct Config {
     api: api::Config,
     tracing: TracingConfig,
 }
+
+async fn run(config: Config) -> Result<()> {
+    info!(?config, "starting");
+
+    api::serve(config.api).await
+}

hello-tracing-common/Cargo.toml

@@ -21,6 +21,7 @@ opentelemetry-otlp    = { workspace = true }
 prost                 = { workspace = true }
 serde                 = { workspace = true }
 serde_json            = { workspace = true }
+time                  = { workspace = true }
 tokio                 = { workspace = true }
 tonic                 = { workspace = true }
 tower                 = { workspace = true }

hello-tracing-common/src/lib.rs

@@ -1,2 +1,18 @@
+use serde_json::json;
+use std::fmt::Display;
+use time::{format_description::well_known::Rfc3339, OffsetDateTime};
+
 pub mod otel;
 pub mod tracing;
+
+pub fn log_error(error: impl Display) {
+    let now = OffsetDateTime::now_utc().format(&Rfc3339).unwrap();
+    let error = serde_json::to_string(&json!({
+        "timestamp": now,
+        "level": "ERROR",
+        "message": "process exited with ERROR",
+        "error": format!("{error:#}")
+    }));
+    // Not using `eprintln!`, because `tracing_subscriber::fmt` uses stdout by default.
+    println!("{}", error.unwrap());
+}

hello-tracing-common/src/tracing.rs

@@ -29,7 +29,7 @@ pub fn init_tracing(config: TracingConfig) -> Result<()> {
 
     tracing_subscriber::registry()
         .with(EnvFilter::from_default_env())
-        .with(fmt::layer().json())
+        .with(fmt::layer().json().flatten_event(true))
         .with(otlp_layer(config)?)
         .try_init()
         .context("initialize tracing subscriber")

hello-tracing-gateway/Dockerfile

@@ -1,4 +1,4 @@
-ARG RUST_VERSION=1.72.1
+ARG RUST_VERSION=1.73.0
 
 FROM rust:${RUST_VERSION}-bullseye AS builder
 RUN apt-get update && \

hello-tracing-gateway/proto

@@ -1 +1 @@
-../hello-tracing-backend/proto/
+../hello-tracing-backend/proto

hello-tracing-gateway/src/main.rs

@@ -4,28 +4,42 @@ mod backend;
 use crate::backend::Backend;
 use anyhow::{Context, Result};
 use configured::Configured;
-use hello_tracing_common::tracing::{init_tracing, TracingConfig};
+use hello_tracing_common::{
+    log_error,
+    tracing::{init_tracing, TracingConfig},
+};
 use serde::Deserialize;
+use std::panic;
 use tracing::{error, info};
 
 #[tokio::main]
-async fn main() -> Result<()> {
-    let config = Config::load().context("load configuration")?;
-    init_tracing(config.tracing.clone()).context("initialize tracing")?;
+async fn main() {
+    // Load configuration first, because needed for tracing initialization.
+    let config = match Config::load().context("load configuration") {
+        Ok(config) => config,
+        Err(error) => {
+            log_error(error);
+            return;
+        }
+    };
 
-    info!(?config, "starting");
+    // If tracing initialization fails, nevertheless emit a structured log event.
+    if let Err(error) = init_tracing(config.tracing.clone()) {
+        log_error(error);
+        return;
+    }
 
-    let backend = Backend::new(config.backend);
-    let result = api::serve(config.api, backend).await;
+    // Replace the default panic hook with one that uses structured logging at ERROR level.
+    panic::set_hook(Box::new(|panic| error!(%panic, "process panicked")));
 
-    if let Err(error) = result {
+    // Run and log any error.
+    if let Err(error) = run(config).await {
         error!(
             error = format!("{error:#}"),
             backtrace = %error.backtrace(),
-            "hello-tracing-gateway exited with ERROR"
+            "process exited with ERROR"
         );
     };
-    Ok(())
 }
 
 #[derive(Debug, Deserialize)]
@@ -35,3 +49,10 @@ struct Config {
     backend: backend::Config,
     tracing: TracingConfig,
 }
+
+async fn run(config: Config) -> Result<()> {
+    info!(?config, "starting");
+
+    let backend = Backend::new(config.backend);
+    api::serve(config.api, backend).await
+}