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 service1) for searching and
monitoring. It can be annoying or impossible to upload log files in
If your organization’s platform supports reading log messages from
regular program output,2 you can just use the default setup, which
log4r includes three additional appenders to facilitate
shipping logs off to an aggregator:
syslog_appender: For writing messages to the system
log on Linux, macOS, and other Unix-like operating systems.
http_appender: For sending log messages as HTTP
tcp_appender: For writing log messages to TCP
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(appenders = syslog_appender("my-R-script"))logger
Requires the rsyslog package.
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(appenders = http_appender("http://logging.example.local"))logger
Some services use
instead of the more intuitive
POST, which you can opt into
<- 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( "http://logging.example.local", method = "GET", layout = default_log_layout(), ::add_headers(`X-Custom-Header` = 1), httr::user_agent("my-r-script/1.0.0") httr ))
Requires the httr package.
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) )