slokit

An SLO and error-budget engine for Rust.

slokit does two things the existing tools (all Go or Python) do not do together:

1. Library core with no serde, YAML, or CLI dependencies, so error-budget and burn-rate math embeds directly inside your services (for example, an Axum handler that reports live budget status).
2. A generator that reads a sloth-compatible YAML spec and emits Prometheus recording rules, metadata rules, and multi-window multi-burn-rate (MWMBR) page/ticket alerts as a single static binary.

It is drop-in compatible with the sloth prometheus/v1 spec, so existing specs work unchanged, and the generated metrics use the same slo:... names and sloth_* labels, so your Grafana dashboards keep working.

Install

cargo install slokit          # the CLI
cargo add slokit              # the library (add `--no-default-features` for the lean core)

CLI

# Generate Prometheus rules from a spec
slokit generate -i slos.yaml -o rules.yaml

# Generate a Prometheus Operator PrometheusRule instead
slokit generate -i slos.yaml --format operator

# Validate a spec without generating
slokit validate -i slos.yaml

# Do the error-budget math from the terminal
slokit calc --objective 99.9 --period 30d --total 1000000 --bad 250

calc output:

Objective:    99.9% over 30d
Error budget: 0.1000% of events
Total events: 1000000
Allowed bad:  1000.00
Observed bad: 250
Burn rate:    0.25x
Consumed:     25.0000%
Remaining:    75.0000%
Exhausted in: 89d 23h

Burn-rate alert thresholds (error ratio that fires each window):
  page   long=1h   short=5m   factor=14.4  threshold=1.4400%
  page   long=6h   short=30m  factor=6     threshold=0.6000%
  ticket long=1d   short=2h   factor=3     threshold=0.3000%
  ticket long=3d   short=6h   factor=1     threshold=0.1000%

Spec format

slokit reads the sloth prometheus/v1 spec, plus one extension: an optional per-SLO period (sloth only offers this as a global flag).

version: "prometheus/v1"
service: myservice
labels:
  owner: team-platform
slos:
  - name: requests-availability
    objective: 99.9
    period: 30d            # slokit extension; defaults to 30d
    sli:
      events:
        error_query: sum(rate(http_requests_total{code=~"5.."}[{{.window}}]))
        total_query: sum(rate(http_requests_total[{{.window}}]))
    alerting:
      name: MyServiceHighErrorRate
      page_alert:
        labels: { severity: page }
      ticket_alert:
        labels: { severity: ticket }

Library

The core has no serialization or CLI dependencies:

use slokit::{Objective, Slo, BurnRate, Window};

let slo = Slo::new(Objective::percent(99.9).unwrap(), Window::days(30));

// With a million events, 0.1% may fail: ~1,000 allowed failures.
let budget = slo.error_budget(1_000_000.0);
assert!((budget.allowed_bad_events() - 1_000.0).abs() < 1e-6);

// A sustained 1% error rate is a 10x burn against a 99.9% objective.
let burn = BurnRate::from_error_ratio(0.01, &slo);
assert!((burn.value() - 10.0).abs() < 1e-9);

Generation lives behind the default spec feature:

use slokit::spec::Spec;
use slokit::generate::generate_rules;

let spec = Spec::from_path("slos.yaml")?;
let ruleset = generate_rules(&spec)?;
println!("{}", ruleset.to_prometheus_yaml()?);
# Ok::<(), slokit::SlokitError>(())

Feature flags

For the lean math-only core: slokit = { version = "0.1", default-features = false }.

The MWMBR model

slokit implements the burn-rate alerting from the Google SRE Workbook. For a 30-day SLO period:

License

Licensed under either of Apache-2.0 or MIT at your option.