Cuts logs in preparation for processing elsewhere.
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♫ I'm a lumberjack and I'm ok! I sleep when idle, then I ship logs all day! I parse your logs, I eat the JVM agent for lunch! ♫

(This project was recently renamed from 'lumberjack' to 'logstash-forwarder' to make its intended use clear. The 'lumberjack' name now remains as the network protocol, and 'logstash-forwarder' is the name of the program. It's still the same lovely log forwarding program you love.)

Questions and support

If you have questions and cannot find answers, please join the #logstash irc channel on freenode irc or ask on the mailing list.

What is this?

A tool to collect logs locally in preparation for processing elsewhere!

Resource Usage Concerns

Perceived Problems: Some users view logstash releases as "large" or have a generalized fear of Java.

Actual Problems: Logstash, for right now, runs with a footprint that is not friendly to underprovisioned systems such as EC2 micro instances; on other systems it is fine. This project will exist until that is resolved.

Transport Problems

Few log transport mechanisms provide security, low latency, and reliability.

The lumberjack protocol used by this project exists to provide a network protocol for transmission that is secure, low latency, low resource usage, and reliable.


logstash-forwarder is configured with a json file you specify with the -config flag:

logstash-forwarder -config yourstuff.json

Here's a sample, with comments in-line to describe the settings. Please please please keep in mind that comments are technically invalid in JSON, so you can't include them in your config.:

  # The network section covers network configuration :)
  "network": {
    # A list of downstream servers listening for our messages.
    # logstash-forwarder will pick one at random and only switch if
    # the selected one appears to be dead or unresponsive
    "servers": [ "localhost:5043" ],

    # The path to your client ssl certificate (optional)
    "ssl certificate": "./logstash-forwarder.crt",
    # The path to your client ssl key (optional)
    "ssl key": "./logstash-forwarder.key",

    # The path to your trusted ssl CA file. This is used
    # to authenticate your downstream server.
    "ssl ca": "./logstash-forwarder.crt",

    # Network timeout in seconds. This is most important for
    # logstash-forwarder determining whether to stop waiting for an
    # acknowledgement from the downstream server. If an timeout is reached,
    # logstash-forwarder will assume the connection or server is bad and
    # will connect to a server chosen at random from the servers list.
    "timeout": 15

  # The list of files configurations
  "files": [
    # An array of hashes. Each hash tells what paths to watch and
    # what fields to annotate on events from those paths.
      "paths": [ 
        # single paths are fine
        # globs are fine too, they will be periodically evaluated
        # to see if any new files match the wildcard.

      # A dictionary of fields to annotate on each event.
      "fields": { "type": "syslog" }
    }, {
      # A path of "-" means stdin.
      "paths": [ "-" ],
      "fields": { "type": "stdin" }
    }, {
      "paths": [
      "fields": { "type": "apache" }


  • Minimize resource usage where possible (CPU, memory, network).
  • Secure transmission of logs.
  • Configurable event data.
  • Easy to deploy with minimal moving parts.
  • Simple inputs only:
    • Follows files and respects rename/truncation conditions.
    • Accepts STDIN, useful for things like varnishlog | logstash-forwarder....

Building it

  1. Install go

  2. Compile logstash-forwarder

     git clone git://
     cd logstash-forwarder
     go build

Packaging it (optional)

You can make native packages of logstash-forwarder.

To build the packages, you will need ruby and fpm installed.

gem install fpm

Now build an rpm:

    make rpm


    make deb

Installing it (via packages only)

If you don't use rpm or deb make targets as above, you can skip this section.

Packages install to /opt/logstash-forwarder.

There are no run-time dependencies.

Running it


logstash-forwarder -config logstash-forwarder.conf

See logstash-forwarder -help for all the flags

The config file is documented further up in this file.

Key points

  • You'll need an SSL CA to verify the server (host) with.
  • You can specify custom fields for each set of paths in the config file. Any number of these may be specified. I use them to set fields like type and other custom attributes relevant to each log.

Generating an ssl certificate

Logstash supports all certificates, including self-signed certificates. To generate a certificate, you can run the following command:

$ openssl req -x509 -batch -nodes -newkey rsa:2048 -keyout logstash-forwarder.key -out logstash-forwarder.crt

This will generate a key at logstash-forwarder.key and the certificate at logstash-forwarder.crt. Both the server that is running logstash-forwarder as well as the logstash instances receiving logs will require these files on disk to verify the authenticity of messages.

Recommended file locations:

  • certificates: /etc/pki/tls/certs
  • keys: /etc/pki/tls/private

Use with logstash

In logstash, you'll want to use the lumberjack input, something like:

input {
  lumberjack {
    # The port to listen on
    port => 12345

    # The paths to your ssl cert and key
    ssl_certificate => "path/to/ssl.crt"
    ssl_key => "path/to/ssl.key"

    # Set this to whatever you want.
    type => "somelogs"

Implementation details

Below is valid as of 2012/09/19

Minimize resource usage

  • Sets small resource limits (memory, open files) on start up based on the number of files being watched.
  • CPU: sleeps when there is nothing to do.
  • Network/CPU: sleeps if there is a network failure.
  • Network: uses zlib for compression.

Secure transmission

  • Uses OpenSSL to verify the server certificates (so you know who you are sending to).
  • Uses OpenSSL to transport logs.

Configurable event data

  • The protocol supports sending a string:string map.

Easy deployment

  • The make deb or make rpm commands will package everything into a single DEB or RPM.

Future protocol discussion

I would love to not have a custom protocol, but nothing I've found implements what I need, which is: encrypted, trusted, compressed, latency-resilient, and reliable transport of events.

  • Redis development refuses to accept encryption support, would likely reject compression as well.
  • ZeroMQ lacks authentication, encryption, and compression.
  • Thrift also lacks authentication, encryption, and compression, and also is an RPC framework, not a streaming system.
  • Websockets don't do authentication or compression, but support encrypted channels with SSL. Websockets also require XORing the entire payload of all messages - wasted energy.
  • SPDY is still changing too frequently and is also RPC. Streaming requires custom framing.
  • HTTP is RPC and very high overhead for small events (uncompressable headers, etc). Streaming requires custom framing.


See LICENSE file.