Flesh out readme.

README.md

@@ -1,8 +1,63 @@
-# node_exporter
+# Node exporter
 
-Prometheus exporter with pluggable metric collectors.
+Prometheus exporter for machine metrics, written in Go with pluggable metric
+collectors.
 
-## collectors
+## Available collectors
 
-Which collectors are used is controlled by the --enabledCollectors flag. To see
-all available collectors, use `--printCollectors`.
+By default the build will include the native collectors that expose information
+from /proc.
+
+Which collectors are used is controlled by the `--enabledCollectors` flag.
+
+### Enabled by default
+
+Name     | Description
+---------|------------
+attributes | Exposes attributes from the configuration file. Deprecated, use textfile module instead.
+diskstats | Exposes disk I/O statistics from /proc/diskstats.
+filesystem | Exposes filesystem statistics, such as disk space used.
+loadavg | Exposes load average.
+meminfo | Exposes memory statistics from /proc/meminfo.
+netdev | Exposes network interface statistics from /proc/netstat, such as bytes transferred.
+netstat | Exposes network statistics from /proc/net/netstat. This is the same information as `netstat -s`.
+stat | Exposes various statistics from /proc/stat. This includes CPU usage, boot time, forks and interrupts.
+textfile | Exposes statistics read from local disk. The `--textfile.directory` flag must be set.
+time | Exposes the current system time.
+
+
+### Disabled by default
+
+Name     | Description
+---------|------------
+bonding | Exposes the number of configured and active slaves of Linux bonding interfaces.
+gmond | Exposes statistics from Ganglia.
+interrupts | Exposes detailed interrupts statistics from /proc/interrupts.
+lastlogin | Exposes the last time there was a login.
+megacli | Exposes RAID statistics from MegaCLI.
+ntp | Exposes time drift from an NTP server.
+runit | Exposes service status from [runit](http://smarden.org/runit/).
+
+## Textfile Collector
+
+The textfile collector is similar to the [Pushgateway](https://github.com/prometheus/pushgateway),
+in that it allows exporting of statistics from batch jobs. It can also be used
+to export static metrics, such as what role a machine has. The Pushgateway
+should be used for service-level metrics. The textfile module is for metrics
+that are tied to a machine.
+
+To use set the `--textfile.directory` flag on the Node exporter. The collector
+will pares all files in that directory matching the glob `*.prom` using the
+[text format](http://prometheus.io/docs/instrumenting/exposition_formats/).
+
+To atomically push completion time for a cron job:
+```
+echo my_batch_job_completion_time $(date +%s) > /path/to/directory/my_batch_job.prom.$$
+mv /path/to/directory/my_batch_job.prom.$$ /path/to/directory/my_batch_job.prom
+```
+
+To statically set roles for a machine using labels:
+```
+echo 'role{role="application_server"} 1' > /path/to/directory/role.prom.$$
+mv /path/to/directory/role.prom.$$ /path/to/directory/role.prom
+```