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Singer logo   Singer

High-performance, reliable and extensible logging agent

Singer is a high performance logging agent for uploading logs to Kafka. It can also be extended to support writing to other message transporters or storage systems.

Singer runs as a standalone process on the service boxes. It monitors the log directories by listening to file system events, and uploads data once it detects new data. Singer guarantees at least one time delivery of log messages.

Key Features:

  • Support thrift log format and text log format out-of-box: Thrift log format provides better throughput and efficiency. We highly recommend you use thrift log format if your logs will not be consumed directly by humans. To facilitate thrift log format usage, we build a set of client libraries in Python, Java, and Go for converting text log messages into JSON and thrift formats.

  • At-least-once message delivery to Kafka: Singer will retry when it fails to upload a batch of messages. For each log stream, Singer uses a watermark file to track its progress. When Singer restarts, it processes messages from the watermark position.

  • Support logging in Kubernetes as a side-car service. Logging in Kubernetes as a daemonset. Singer can monitor and upload loads from log directories of multiple Kubernetes pods.

  • High throughput writes to Kafka: Singer uses multiple layers of thread pool to achieve maximum parallelism. Using thrift log format, Singer can achieve >100MB/second writing throughput to Kafka from one host. Singer can process text logs at 20MB/second.

  • Low latency logging: Singer supports configurable processing latency and batch sizes, it can achieve <5ms log uploading latency.

  • Flexible partitioning: Singer provides multiple partitioners for writing data to Kafka, including locality aware partitioners that can avoid producer traffic across availability zones and reduce data transfer costs. Singer also supports customized partitioner.

  • Heartbeat: Singer supports sending heartbeats to a kafka topic periodically based on the configuration. This allows the users to set up central monitoring of Singer instances across fleets.

  • Write auditing: Singer can write an audit message to another topic for each batch of messages that it writes to kafka. This allow users to audit Singer kafka writes.

  • Extensible design: Singer can be easily extended to support data uploading to custom destinations.

Detailed design

Please see docs/ on Singer design.


Get Singer code

git clone [git-repo-url] singer
cd singer

Build Singer binary

mvn clean package -pl singer -am -DskipTests

As there is no native support in JDK for file system events monitoring on Mac OSX, some tests that run fine in the Linux environment may fail intermittently on Mac OSX. Please use -DskipTests flag if you want to build Singer on macOS.

Build thift-logger client library

mvn clean package -pl thrift-logger -am


Singer has a set of unit tests that can be run through mvn test package -pl singer -am.

An end-to-end integration test that can be run through:

mvn clean package -pl singer -am 

Quick Start

The tutorial directory contains a demo that shows how to run Singer. Please see tutorial/ for details.


Use Singer client library to log data to local disk

Singer uses file inode + offset as the watermark position to track its progress, and writes the watermark info to disk after it writes a batch of messages to kafka. It resumes from the last watermark position after restarting. Because of this, Singer requires that a log stream is a sequence of append-only log files, and uses file renaming for log rotation.

Singer does not handle log streams that use file copy and truncation for log rotation, because Singer cannot use file inode + offset to uniquely identify log messages when a log file is copied and truncated.

For example, we have before rotation:

ls -li 
  1001    service.log      # service.log with inode 1001

after rotation

 ls -li 
   1001   service.log.2018-11-30   # service.log.2018-11-30 with inode 1001 (was renamed from the old service.log)
   1002   service.log              # (this was newly generated service.log)

For logged data in plaintext format, you can directly config Singer to upload those logs. Singer also support high throughput logging using thrift format. You can write data to local disk using thrift-logger library that Singer provides. Currently Singer has thrift_logger libraries in Python, Java, Go, and C++.

Samples on using thrift_logger libraies:

Config Singer to upload data from local disk to Kafka

Singer uploads data based on configuration settings. Singer configuration is composed of two parts: 1) that configures global Singer settings, e.g. size of thread pools, daily restart settings, heartbeat settings, etc. 2) log stream configuration: for each set of log streams, singer needs one log stream configuration to define log stream related settings.

Please see tutorial/etc/singer for singer configurations. docs/configuration_samples/sample_kubernetes has an example on Singer configuration for Kubernetes.

Run Singer

java -server  -cp $singer_home:$singer_home/lib/*:$singer_home/singer-$version.jar  \ -Dsinger.config.dir=$config_dir \

Package Singer as a debian package

tar xzvf singer-${VERSION}-bin.tar.gz --directory $SINGER_DIR

fpm -s dir -t deb -n singer -v $VERSION --deb-upstart ../singer.upstart  \
    --deb-default ../singer.default -- .

Singer Metrics

Singer exposes metrics using Twitter Ostrich framework. Singer stats can be checked using the following command. Here 2047 is the ostrich port that you define in singer.ostrichPort configuration.

curl -s localhost:2047/stats.txt


Singer is distributed under Apache License, Version 2.0.


A high-performance, reliable and extensible logging agent for uploading data to Kafka, Pulsar, etc.



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