logging: support output to stderr (#5896)

(part of the getpage benchmarking epic #5771)

The plan is to make the benchmarking tool log on stderr and emit results
as JSON on stdout. That way, the test suite can simply take captures
stdout and json.loads() it, while interactive users of the benchmarking
tool have a reasonable experience as well.

Existing logging users continue to print to stdout, so, this change
should be a no-op functionally and performance-wise.

control_plane/src/bin/attachment_service.rs

@@ -286,6 +286,7 @@ async fn main() -> anyhow::Result<()> {
     logging::init(
         LogFormat::Plain,
         logging::TracingErrorLayerEnablement::Disabled,
+        logging::Output::Stdout,
     )?;
 
     let args = Cli::parse();

libs/remote_storage/tests/test_real_azure.rs

@@ -281,6 +281,7 @@ fn ensure_logging_ready() {
         utils::logging::init(
             utils::logging::LogFormat::Test,
             utils::logging::TracingErrorLayerEnablement::Disabled,
+            utils::logging::Output::Stdout,
         )
         .expect("logging init failed");
     });

libs/remote_storage/tests/test_real_s3.rs

@@ -210,6 +210,7 @@ fn ensure_logging_ready() {
         utils::logging::init(
             utils::logging::LogFormat::Test,
             utils::logging::TracingErrorLayerEnablement::Disabled,
+            utils::logging::Output::Stdout,
         )
         .expect("logging init failed");
     });

libs/utils/src/logging.rs

@@ -66,9 +66,17 @@ pub enum TracingErrorLayerEnablement {
     EnableWithRustLogFilter,
 }
 
+/// Where the logging should output to.
+#[derive(Clone, Copy)]
+pub enum Output {
+    Stdout,
+    Stderr,
+}
+
 pub fn init(
     log_format: LogFormat,
     tracing_error_layer_enablement: TracingErrorLayerEnablement,
+    output: Output,
 ) -> anyhow::Result<()> {
     // We fall back to printing all spans at info-level or above if
     // the RUST_LOG environment variable is not set.
@@ -85,7 +93,12 @@ pub fn init(
         let log_layer = tracing_subscriber::fmt::layer()
             .with_target(false)
             .with_ansi(false)
-            .with_writer(std::io::stdout);
+            .with_writer(move || -> Box<dyn std::io::Write> {
+                match output {
+                    Output::Stdout => Box::new(std::io::stdout()),
+                    Output::Stderr => Box::new(std::io::stderr()),
+                }
+            });
         let log_layer = match log_format {
             LogFormat::Json => log_layer.json().boxed(),
             LogFormat::Plain => log_layer.boxed(),

pageserver/src/bin/pageserver.rs

@@ -103,7 +103,11 @@ fn main() -> anyhow::Result<()> {
     } else {
         TracingErrorLayerEnablement::Disabled
     };
-    logging::init(conf.log_format, tracing_error_layer_enablement)?;
+    logging::init(
+        conf.log_format,
+        tracing_error_layer_enablement,
+        logging::Output::Stdout,
+    )?;
 
     // mind the order required here: 1. logging, 2. panic_hook, 3. sentry.
     // disarming this hook on pageserver, because we never tear down tracing.

pageserver/src/tenant.rs

@@ -3504,6 +3504,7 @@ pub(crate) mod harness {
                 // enable it in case the tests exercise code paths that use
                 // debug_assert_current_span_has_tenant_and_timeline_id
                 logging::TracingErrorLayerEnablement::EnableWithRustLogFilter,
+                logging::Output::Stdout,
             )
             .expect("Failed to init test logging")
         });

safekeeper/src/bin/safekeeper.rs

@@ -202,6 +202,7 @@ async fn main() -> anyhow::Result<()> {
     logging::init(
         LogFormat::from_config(&args.log_format)?,
         logging::TracingErrorLayerEnablement::Disabled,
+        logging::Output::Stdout,
     )?;
     logging::replace_panic_hook_with_tracing_panic_hook().forget();
     info!("version: {GIT_VERSION}");

storage_broker/src/bin/storage_broker.rs

@@ -434,6 +434,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     logging::init(
         LogFormat::from_config(&args.log_format)?,
         logging::TracingErrorLayerEnablement::Disabled,
+        logging::Output::Stdout,
     )?;
     logging::replace_panic_hook_with_tracing_panic_hook().forget();
     // initialize sentry if SENTRY_DSN is provided