fix: use environment variables to tune async init - and not system properties (#450)

Author: deki

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/AsyncInitializationWrapper.java

@@ -40,7 +40,7 @@
 public class AsyncInitializationWrapper extends InitializationWrapper {
     private static final int DEFAULT_INIT_GRACE_TIME_MS = 150;
     private static final String INIT_GRACE_TIME_ENVIRONMENT_VARIABLE_NAME = "AWS_SERVERLESS_JAVA_CONTAINER_INIT_GRACE_TIME";
-    private static final int INIT_GRACE_TIME_MS = Integer.parseInt(System.getProperty(
+    private static final int INIT_GRACE_TIME_MS = Integer.parseInt(System.getenv().getOrDefault(
             INIT_GRACE_TIME_ENVIRONMENT_VARIABLE_NAME, Integer.toString(DEFAULT_INIT_GRACE_TIME_MS)));
     private static final int LAMBDA_MAX_INIT_TIME_MS = 10_000;
 
@@ -75,7 +75,8 @@ public void start(LambdaContainerHandler handler) throws ContainerInitialization
             long curTime = Instant.now().toEpochMilli();
             // account for the time it took to call the various constructors with the actual start time + a grace time
             long awaitTime = (actualStartTime + LAMBDA_MAX_INIT_TIME_MS) - curTime - INIT_GRACE_TIME_MS;
-            log.info("Async initialization will wait for " + awaitTime + "ms");
+            log.info("Async initialization will wait for {}ms (init grace time is configured to {})",
+                    awaitTime, INIT_GRACE_TIME_MS);
             if (!initializationLatch.await(awaitTime, TimeUnit.MILLISECONDS)) {
                 log.info("Initialization took longer than " + LAMBDA_MAX_INIT_TIME_MS + ", setting new CountDownLatch and " +
                         "continuing in event handler");

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/model/ContainerConfig.java

@@ -28,7 +28,7 @@ public class ContainerConfig {
     private static final List<String> DEFAULT_FILE_PATHS = new ArrayList<String>() {{ add("/tmp"); add("/var/task"); }};
     private static final int DEFAULT_MAX_INIT_TIMEOUT_MS = 20_000;
     private static final String MAX_INIT_TIMEOUT_ENVIRONMENT_VARIABLE_NAME = "AWS_SERVERLESS_JAVA_CONTAINER_MAX_INIT_TIMEOUT";
-    private static final int MAX_INIT_TIMEOUT_MS = Integer.parseInt(System.getProperty(
+    private static final int MAX_INIT_TIMEOUT_MS = Integer.parseInt(System.getenv().getOrDefault(
             MAX_INIT_TIMEOUT_ENVIRONMENT_VARIABLE_NAME, Integer.toString(DEFAULT_MAX_INIT_TIMEOUT_MS)));
 
     public static ContainerConfig defaultConfig() {