The 12 factor rule for logging says that an app "should not attempt to write to or manage logfiles. Instead, each running process writes its event stream, unbuffered, to stdout." The execution environment should take care of capturing the logs and perform further processing with it. Funnel is this "execution environment".

All you have to do from your app is to print your log line to stdout, and pipe it to funnel. You can still use any logging library inside your app to handle other stuff like log level, structured logging etc. But don't bother about the log destination. Let funnel take care whether you want to just write to files or stream your output to Kafka. Think of it as a fluentd/logstash replacement(with minimal features!) but having only stdin as an input.

• Basic use case of logging to local files:
  • Rolling over to a new file
  • Deleting old files
  • Gzipping files
  • File rename policies
• Prepend each log line with a custom string
• Supports other target outputs like Kafka, ElasticSearch. More info below.
• Live reloading of config on file save. No more messing around with SIGHUP or SIGUSR1.

Grab the binary for your platform from here.

To run, just pipe the output of your app to the funnel binary. Note that, funnel only consumes from stdin, so you might need to redirect stderr to stdout.

$/etc/myapp/bin 2>&1 | funnel

P.S. You also need to drop the funnel binary to your $PATH.

In the [service] section of your file, add these lines -

[Service]
EnvironmentFile=/path/to/env/file (Can contain funnel environment flags)
ExecStart=/bin/sh -c '/path/to/binary 2>&1 | funnel'
ExecStop=/usr/bin/pkill -TERM -f "/path/to/binary"

Output	Description	Log format
File	Writes to local files	No format needed.
Kafka	Send your log stream to a Kafka topic	No format needed.
Redis pub-sub	Send your log stream to a Redis pub-sub channel	No format needed.
ElasticSearch	Index, Search and Analyze structured JSON logs	Logs have to be in JSON format
Amazon S3	Upload your logs to S3	No format needed.
InfluxDB	Use InfluxDB if your app emits timeseries data which needs to be queried and graphed	Logs have to be in JSON format with tags and fields as the keys
NATS	Send your log stream to a NATS subject	No format needed.

Further details on input log format along with examples can be found in the sample config file.

The config can be specified in a .toml file. The file is part of the repo, which you can see here. All the settings are documented and are populated with the default values. The same defaults are embedded in the app itself, so the app can even run without a config file.

To read the config, the app looks for a file named funnel.toml in these locations one by one -

• /etc/funnel/funnel.toml
• $HOME/.config/funnel/funnel.toml
• ./funnel.toml (i.e. in the current directory of your target app)

You can place a global file in /etc/funnel/ and have separate files in each app directory to have config values overriding the global ones.

Environment variables are also supported and takes the highest precedence. To get the env variable name, just capitalize the config variable. For eg-

• logging.directory becomes LOGGING_DIRECTORY
• rollup.file_rename_policy becomes ROLLUP_FILE_RENAME_POLICY

In the case that you don't intend to use the Elasticsearch, InfluxDB, Kafka, Redis or S3 features, e.g. you just want to use the log rotation features, you can reduce the size of the binary by using build tags.

The build tags are:

• disableelasticsearch
• disableinfluxdb
• disablekafka
• disableredis
• disables3
• disablenats

e.g., to build without any of the above outputs:

go build -tags "disableelasticsearch disableinfluxdb disablekafka disableredis disables3 disablenats" ./cmd/funnel

Funnel logs its internal errors to syslog. As syslog is not supported on windows, funnel doesn't work on windows - https://golang.org/pkg/log/syslog/#pkg-note-BUG

To make it work on windows, just replace the syslog writer with another logging library which atleast has an Err() method implemented.