logfileng - write a logfile with rotation

Writes a log file of the status of monitors. Rotates and deletes old log files based on size or age.

The logfile format is:

datetime monitor-name: status; VFC=vfc (message) (execution-time)

where the fields have the following meanings:

datetime: the datetime of the entry. Format is controlled by the dateformat configuration option.
monitor-name: the name of the monitor
status: either ok if the monitor succeeded, or failed since YYYY-MM-DD HH:MM:SS
vfc: the virtual failure count: the number of failures of the monitor beyond its tolerance. Not present for ok lines.
message: the message the monitor recorded as the reason for failure. Not present for ok lines.
execution-time: the time the monitor took to execute its check

filename

Type: string
Required: true

the filename to write to. Rotated logs have either .N (where N is an incrementing number) or the date/time appended to the filename, depending on the rotation mode.

rotation_type

Type: string
Required: true

one of time or size

when

Type: string
Required: false
Default: h

Only for rotation based on time. The units represented by interval. One of s for seconds, m for minutes, h for hours, or d for days

interval

Type: integer
Required: false
Default: 1

Only for rotation based on time. The number of when between file rotations.

max_bytes

Type: bytes
Required: yes, when rotation_type is size

the maximum log file size before it is rotated.

backup_count

Type: integer
Required: false
Default: 1

the number of old files to keep

only_failures

Type: boolean
Required: false
Default: false

set to have only monitor failures written to the log file (almost, but not quite, turning it into an alerter)