prom_calc.py

#!/bin/env python3
#
# Gets the estimated space usage of prometheus
#
# usage: /opt/prom_calc.py 1y [optional number of samples per sec]
#    y = years
#    m = months
#    d = days
#
# If number of samples not provided, queries from prometheus on prometheus.mydomain.com:9090
#
# Author: Paul Reece 
# 2023-07-12

from datetime import timedelta
import sys
import re
import requests

PROMETHEUS='http://prometheus.mydomain.com:9090'

if re.search('[0-9]{1,4}y', sys.argv[1]):
    days = int(sys.argv[1].split('y')[0]) * 365
    retention_time_seconds = int(timedelta(days).total_seconds())
elif re.search('[0-9]{1,4}m', sys.argv[1]):
    days = int(sys.argv[1].split('m')[0]) * 30
    retention_time_seconds = int(timedelta(days).total_seconds())
if re.search('[0-9]{1,4}d', sys.argv[1]):
    days = int(sys.argv[1].split('d')[0])
    retention_time_seconds = int(timedelta(days).total_seconds())
else:
    retention_time_seconds = int(timedelta(days).total_seconds())

if len(sys.argv) > 2:
    ingested_samples_per_second = sys.argv[2]
else:
    r = requests.get(PROMETHEUS + '/api/v1/query?query=rate(prometheus_tsdb_head_samples_appended_total[24h])')
    r = r.json()
    if r['status'] != 'success':
        print("failed to query prometheus at " + PROMETHEUS)
        print("provide samples per second manually or change endpoint or run the script from another place that has access")
        os.exit(2)
    else:
        ingested_samples_per_second = int(r['data']['result'][0]['value'][1].split('.')[0])

bytes_per_sample = int(2) # from prometheus docs https://prometheus.io/docs/prometheus/latest/storage/

def sizeof_fmt(num, suffix="B"):
    for unit in ("", "Ki", "Mi", "Gi", "Ti", "Pi", "Ei", "Zi"):
        if abs(num) < 1024.0:
            return f"{num:3.1f}{unit}{suffix}"
        num /= 1024.0
    return f"{num:.1f}Yi{suffix}"

needed_disk_space = int(retention_time_seconds) * int(ingested_samples_per_second) * int(bytes_per_sample) # also from prom docs

print("Estimated disk space " + sizeof_fmt(needed_disk_space))