promcron

promcron

promcron is cron service which can also export prometheus metrics.

Because promcron uses a simple and robust time keeping algorithm, it is not suited for thousands of jobs, but in exchange is able to detect time keeping anomalies which are exported as a metric.

How promcron handles some edge cases:

• If a job is overdue, promcron logs it, but does not run it.
• If time jumps forward more than 30 seconds, promcron may miss jobs but attempts to log them and export time anomaly metrics.
• If time jumps backwards more than 30 seconds, promcron may run jobs multiple times, but attempts to log them and export time anomaly metrics.

Example

/etc/promcron:

# All fields are mandatory
#         ┌───────────── minute (0 - 59)
#         │ ┌───────────── hour (0 - 23)
#         │ │ ┌───────────── day of the month (1 - 31)
#         │ │ │ ┌───────────── month (1 - 12, jan-dec)
#         │ │ │ │ ┌───────────── day of the week (0 - 6, mon-sun) 
#         │ │ │ │ │
#         │ │ │ │ │
job-label 0 * * * * echo 'An hour has passed'
# Repeat and range syntax
job2 */10 * * * * echo 'Every 10 minutes'
job3 0-5  * * * * echo 'First 5 minutes of each hour'

Run promcron:

$ promcron -prometheus-metrics 127.0.0.1:1234 -f /etc/promcron

Example of exported metrics

The table:

job1 0/2 * * * * echo hello
job2 1/2 * * * * sleep 300

produces the following exported metrics:

...
promcron_job_duration_seconds{job="job1"} 0.003607821
promcron_job_duration_seconds{job="job2"} 300.006504244
promcron_job_failure_count{job="job1"} 0
promcron_job_failure_count{job="job2"} 0
promcron_job_maxrss_bytes{job="job1"} 5.2236288e+07
promcron_job_maxrss_bytes{job="job2"} 2.3601152e+07
promcron_job_overdue_count{job="job1"} 0
promcron_job_overdue_count{job="job2"} 2
promcron_job_running{job="job1"} 0
promcron_job_running{job="job2"} 1
promcron_job_stime_seconds{job="job1"} 0.001138
promcron_job_stime_seconds{job="job2"} 0.003096
promcron_job_success_count{job="job1"} 5
promcron_job_success_count{job="job2"} 1
promcron_job_utime_seconds{job="job1"} 0.002276
promcron_job_utime_seconds{job="job2"} 0.003096