Ladle: a method for unsupervised anomaly detection across log types

Abstract Log files can help detect and diagnose erroneous software behaviour, but their utility is limited by the ability of users and developers to sift through large amounts of text. Unsupervised machine learning tools have been developed to automatically find anomalies in logs, but they are usually not designed for situations where a large number of log streams or log files, each with its own characteristics, need to be analyzed and their anomaly scores compared. We propose Ladle, an accurate unsupervised anomaly detection and localization method that can simultaneously learn the characteristics of hundreds of log types and determine which log entries are the most anomalous across these log types. Ladle uses a sentence transformer (a large language model) to embed short overlapping segments of log files and compares new, potentially anomalous, log segments against a collection of reference data. The result of the comparison is re-centered by subtracting a baseline score indicating how much variation tends to occur in each log type, making anomaly scores comparable across log types. Ladle is designed to adapt to data drift and is updated by adding new reference data without the need to retrain the sentence transformer. We demonstrate the accuracy of Ladle on a real-world dataset consisting of logs produced by an endpoint protection platform test suite. We also compare Ladle’s performance on the dataset to that of a state-of-the-art method for single-log anomaly detection, showing that the latter is inadequate for the multi-log task.