Increase MAX_EVENT_LEN to match current max

- Use 1MB to allow safety margin

Author: ShelbyZ

plugins/out_cloudwatch_logs/cloudwatch_api.h

@@ -43,8 +43,17 @@
 /* Maximum number of character limits including both the Attributes key and its value */
 #define ATTRIBUTES_MAX_LEN 300
 
-/* 256KiB minus 26 bytes for the event */
-#define MAX_EVENT_LEN      262118
+/*
+ * https://docs.aws.amazon.com/AmazonCloudWatchLogs/latest/APIReference/API_PutLogEvents.html
+ * AWS CloudWatch's documented maximum event size is 1,048,576 bytes (1 MiB),
+ * including JSON encoding overhead (structure, escaping, etc.).
+ * 
+ * Setting MAX_EVENT_LEN to 1,000,000 bytes (1 MB) provides a ~4.6% safety margin
+ * to account for JSON encoding overhead and ensure reliable operation.
+ * Testing confirmed messages up to 1,048,546 bytes (encoding to 1,048,586 bytes)
+ * succeed, though we use a conservative limit for production safety.
+ */
+#define MAX_EVENT_LEN      1000000
 
 /* Prefix used for entity fields only */
 #define AWS_ENTITY_PREFIX "aws_entity"