feat: add environment variable support for runtime interface emulator address

Add support for RUNTIME_INTERFACE_EMULATOR_ADDRESS environment variable
to configure the emulator address without requiring CLI flags.

This enables easier configuration in containerized environments where
modifying the entrypoint script is not practical. The implementation
follows the same pattern as LOG_LEVEL handling.

Features:
- Environment variable RUNTIME_INTERFACE_EMULATOR_ADDRESS support
- CLI flag takes precedence over environment variable (AWS CLI pattern)
- Updated help text to document the environment variable
- Added integration tests for environment variable usage
- Added test for CLI flag precedence over environment variable

Fixes #120

Author: cnaples79

cmd/aws-lambda-rie/main.go

@@ -27,7 +27,7 @@ type options struct {
 	InitCachingEnabled bool   `long:"enable-init-caching" description:"Enable support for Init Caching"`
 	// Do not have a default value so we do not need to keep it in sync with the default value in lambda/rapidcore/sandbox_builder.go
 	RuntimeAPIAddress               string `long:"runtime-api-address" description:"The address of the AWS Lambda Runtime API to communicate with the Lambda execution environment."`
-	RuntimeInterfaceEmulatorAddress string `long:"runtime-interface-emulator-address" default:"0.0.0.0:8080" description:"The address for the AWS Lambda Runtime Interface Emulator to accept HTTP request upon."`
+	RuntimeInterfaceEmulatorAddress string `long:"runtime-interface-emulator-address" default:"0.0.0.0:8080" description:"The address for the AWS Lambda Runtime Interface Emulator to accept HTTP request upon. Can also be set by the environment variable 'RUNTIME_INTERFACE_EMULATOR_ADDRESS'."`
 }
 
 func main() {
@@ -49,6 +49,14 @@ func main() {
 
 	rapidcore.SetLogLevel(logLevel)
 
+	// Handle RuntimeInterfaceEmulatorAddress environment variable
+	// If CLI flag not provided, check environment variable
+	if opts.RuntimeInterfaceEmulatorAddress == "0.0.0.0:8080" {
+		if envAddress, envAddressSet := os.LookupEnv("RUNTIME_INTERFACE_EMULATOR_ADDRESS"); envAddressSet {
+			opts.RuntimeInterfaceEmulatorAddress = envAddress
+		}
+	}
+
 	if opts.RuntimeAPIAddress != "" {
 		_, _, err := net.SplitHostPort(opts.RuntimeAPIAddress)
 

test/integration/local_lambda/test_end_to_end.py

@@ -235,6 +235,30 @@ def test_port_override(self):
             self.assertEqual(b'"My lambda ran succesfully"', r.content)
 
 
+    def test_runtime_interface_emulator_address_env_var(self):
+        image, rie, image_name = self.tagged_name("rie_address_env_var")
+
+        # Use port 8081 inside the container and set via environment variable instead of CLI flag
+        params = f"--name {image} -d -v {self.path_to_binary}:/local-lambda-runtime-server -p {self.PORT}:8081 -e RUNTIME_INTERFACE_EMULATOR_ADDRESS=0.0.0.0:8081 --entrypoint /local-lambda-runtime-server/{rie} {image_name} {DEFAULT_1P_ENTRYPOINT} main.success_handler"
+
+        with self.create_container(params, image):
+            r = self.invoke_function()
+        
+            self.assertEqual(b'"My lambda ran succesfully"', r.content)
+
+
+    def test_runtime_interface_emulator_address_cli_precedence(self):
+        image, rie, image_name = self.tagged_name("rie_address_cli_precedence")
+
+        # Set environment variable but override with CLI flag - CLI should take precedence  
+        params = f"--name {image} -d -v {self.path_to_binary}:/local-lambda-runtime-server -p {self.PORT}:8082 -e RUNTIME_INTERFACE_EMULATOR_ADDRESS=0.0.0.0:8080 --entrypoint /local-lambda-runtime-server/{rie} {image_name} {DEFAULT_1P_ENTRYPOINT} main.success_handler --runtime-interface-emulator-address 0.0.0.0:8082"
+
+        with self.create_container(params, image):
+            r = self.invoke_function()
+        
+            self.assertEqual(b'"My lambda ran succesfully"', r.content)
+
+
     def test_custom_client_context(self):
         image, rie, image_name = self.tagged_name("custom_client_context")