Logging Beyond Local Files

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For local development or simple batch R scripts run manually, writing log messages to a file for later inspection (with file_appender) is quite convenient. However, for deployed R applications (like Shiny apps and Plumber APIs) or automated scripts it is more likely that all an organization's logs will be aggregated in one central place (perhaps with a commercial tool or service[^1]) for searching and monitoring. It can be annoying or impossible to upload log files in these cases.

If your organization's platform supports reading log messages from regular program output,[^2] you can just use the default setup, which uses the console_appender(). Otherwise, log4r includes three additional appenders to facilitate shipping logs off to an aggregator:

Writing to the System Log

The Unix "System log" (syslog) dates to the mid-1980s, and is still widely used. Almost all log aggregation services support ingesting a server's syslog messages, so often the easiest way to get your logs to these services is to make your R talk to the local syslog.

To use the syslog_appender, all you need is an identifier for your R app or script:

logger <- logger(appenders = syslog_appender("my-R-script"))

Requires the rsyslog package.

Sending Logs over HTTP

If you're not already forwarding syslog messages (or need to send logs from Windows), the next most-common approach is to send them over HTTP. Log aggregation services usually provide an HTTP API endpoint to facilitate this:

logger <- logger(appenders = http_appender("http://logging.example.local"))

Some services use GET or PUT requests instead of the more intuitive POST, which you can opt into as follows:

logger <- logger(
  appenders = http_appender("http://logging.example.local", method = "GET")

Finally, if you need complete control over the HTTP request (for example, to send a specific header or use authentication), you can pass additional parameters to the underlying httr verb function:

logger <- logger(
  appenders = http_appender(
    method = "GET",
    layout = default_log_layout(),
    httr::add_headers(`X-Custom-Header` = 1),

Requires the httr package.

Writing Directly to TCP Connections

For some workloads, the send-and-receive structure of HTTP requests may be undesirable, so many log aggregators also accept messages directly at a TCP port:

logger <- logger(
  appenders = tcp_appender("tcp://logging.example.local", port = 9551)

[^1]: Such as Splunk or Loggly. There is also are also many open-source options, such as the ELK Stack or Graylog.

[^2]: For example, when running as a Docker container in a cluster with all logs forwarded automatically, or when scripts are wrapped up as SystemD unit files.

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log4r documentation built on Nov. 4, 2021, 9:09 a.m.