monitor.check-status

export function aggregateStatus(statuses: readonly CheckStatus[], downQuorum: number): CheckStatus

export type CheckStatus = "up" | "degraded" | "down";

/** One probe outcome at a moment, the unit every monitor.* series is made of. */
export interface Check {
  /** Unix seconds when the probe ran */
  readonly at: number;
  readonly status: CheckStatus;
}

import { aggregateStatus } from "#fune/monitor.check-status@^1";

import { type CheckStatus } from "./monitor_check_status_types.ts";

/**
 * One status for a target probed from several places. Down needs a quorum,
 * so one location with a broken route cannot page anyone; a down vote below
 * the quorum still counts as degraded, because something is wrong somewhere.
 */
export function aggregateStatus(statuses: readonly CheckStatus[], downQuorum: number): CheckStatus {
  if (statuses.length === 0) throw new RangeError("statuses must not be empty");
  if (!Number.isSafeInteger(downQuorum) || downQuorum < 1 || downQuorum > statuses.length) {
    throw new RangeError(`downQuorum must be 1 to ${statuses.length}, received ${downQuorum}`);
  }
  let down = 0;
  let degraded = 0;
  for (const s of statuses) {
    if (s === "down") down += 1;
    else if (s === "degraded") degraded += 1;
    else if (s !== "up") throw new RangeError(`unknown check status: ${String(s)}`);
  }
  if (down >= downQuorum) return "down";
  return down > 0 || degraded > 0 ? "degraded" : "up";
}

Install

fune build

With that line in your source, in a TypeScript project (language typescript in fune.project), fune build resolves it and nothing else, pins them in fune.lock, downloads only the TypeScript package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add monitor.check-status

The manifest, vectors and README with only the TypeScript implementation. Install it without the registry with fune add ./monitor.check-status-1.0.0-typescript.fune, or fetch it from a terminal with fune pull monitor.check-status@1.0.0:typescript.

The whole function, every language, is one file too: monitor.check-status-1.0.0.fune, 9,013 bytes, sha256 be76e5bc993feafeee52850214d86b9e76091db0f91f029ed87fadc0576185ff. It installs into a project of any language.

// fune: before monitor.check-status

// fune: after monitor.check-status

// fune: step monitor.check-status after <n|label>

More from the author

## aggregateStatus

Monitoring services confirm an outage from more than one location before alerting, because a single probe location with a bad route is far more common than a real outage. The rule, in order:

1. At least `downQuorum` statuses are `down`: **down**. 2. Any `down` (below the quorum) or any `degraded`: **degraded**. Something is wrong somewhere, but not enough to call it an outage. 3. Otherwise **up**.

Degraded votes never add up to down, however many there are: a slow site is still serving.

## Errors

- `statuses must not be empty` - `downQuorum must be 1 to N` where N is the number of statuses: a quorum that can never be met would hide every outage. - `unknown check status: X`

Files