feat(lambda-lite): detect Lambda Lite environment and write mini agent sentinel file

.gitignore

@@ -1,3 +1,4 @@
 /target
 /.idea
+/.worktrees
 

Cargo.toml

@@ -15,6 +15,7 @@ repository = "https://github.com/DataDog/serverless-components"
 
 [profile.release]
 opt-level = "z"
-lto = true
+lto = "fat"
 codegen-units = 1
-strip = true
+strip = "symbols"
+panic = "abort"

crates/datadog-trace-agent/src/http_utils.rs

@@ -114,6 +114,23 @@ pub fn verify_request_content_length(
     None
 }
 
+/// Environment variable set by the Lambda runtime to indicate the initialisation type.
+/// Lambda Lite (web function / snap-start mode) sets this to `"native-http"`;
+/// standard on-demand invocations set it to `"on-demand"`.
+const ENV_LAMBDA_INIT_TYPE: &str = "AWS_LAMBDA_INITIALIZATION_TYPE";
+
+/// Returns true if the current environment is Lambda Lite (web function / snap start mode).
+///
+/// Determined by checking [`ENV_LAMBDA_INIT_TYPE`]` == "native-http"`. This is used to gate
+/// behaviour specific to long-running web server deployments on Lambda Lite.
+pub fn is_lambda_lite() -> bool {
+    is_lambda_lite_from_env(std::env::var(ENV_LAMBDA_INIT_TYPE).ok().as_deref())
+}
+
+fn is_lambda_lite_from_env(val: Option<&str>) -> bool {
+    val == Some("native-http")
+}
+
 /// Builds a reqwest client with optional proxy configuration and timeout.
 /// Uses rustls TLS by default. FIPS-compliant TLS is available via the fips feature
 pub fn build_client(
@@ -135,8 +152,29 @@ mod tests {
     use hyper::StatusCode;
     use libdd_common::hyper_migration;
 
+    use super::is_lambda_lite_from_env;
     use super::verify_request_content_length;
 
+    #[test]
+    fn test_is_lambda_lite_native_http() {
+        assert!(is_lambda_lite_from_env(Some("native-http")));
+    }
+
+    #[test]
+    fn test_is_lambda_lite_on_demand() {
+        assert!(!is_lambda_lite_from_env(Some("on-demand")));
+    }
+
+    #[test]
+    fn test_is_lambda_lite_empty_string() {
+        assert!(!is_lambda_lite_from_env(Some("")));
+    }
+
+    #[test]
+    fn test_is_lambda_lite_unset() {
+        assert!(!is_lambda_lite_from_env(None));
+    }
+
     fn create_test_headers_with_content_length(val: &str) -> HeaderMap {
         let mut map = HeaderMap::new();
         map.insert(header::CONTENT_LENGTH, val.parse().unwrap());

crates/datadog-trace-agent/src/mini_agent.rs

@@ -31,6 +31,10 @@ const PROFILING_ENDPOINT_PATH: &str = "/profiling/v1/input";
 const TRACER_PAYLOAD_CHANNEL_BUFFER_SIZE: usize = 10;
 const STATS_PAYLOAD_CHANNEL_BUFFER_SIZE: usize = 10;
 const PROXY_PAYLOAD_CHANNEL_BUFFER_SIZE: usize = 10;
+/// Sentinel file written on startup in Lambda Lite mode.
+/// dd-trace (Node.js) checks this path via DATADOG_MINI_AGENT_PATH in constants.js
+/// to decide whether to switch from LogExporter (stdout) to AgentExporter (HTTP :8126).
+const LAMBDA_LITE_SENTINEL_PATH: &str = "/tmp/datadog/mini_agent_ready";
 
 pub struct MiniAgent {
     pub config: Arc<config::Config>,
@@ -147,6 +151,18 @@ impl MiniAgent {
             now.elapsed().as_millis()
         );
 
+        // Write a sentinel file so that Node.js dd-trace detects a running agent and
+        // switches from LogExporter (stdout) to AgentExporter (HTTP :8126).
+        // Only written for Lambda Lite; standard Lambda invocations use the Lambda
+        // Extension path (/opt/extensions/datadog-agent) instead.
+        // /opt is read-only in Lambda Lite, so we use /tmp/datadog/ (created by the
+        // serverless-compat JS layer before spawning this binary).
+        if crate::http_utils::is_lambda_lite() {
+            if let Err(e) = std::fs::write(LAMBDA_LITE_SENTINEL_PATH, b"") {
+                debug!("Could not write mini agent sentinel file: {}", e);
+            }
+        }
+
         if let Some(pipe_name) = pipe_name_opt {
             // Windows named pipe transport
             #[cfg(all(windows, feature = "windows-pipes"))]