cloudflare-domain-manager/apps/api/src/services/routing/failover.ts

import type { LbIpRow } from "./types.js";
import { isPoolMember } from "./health.js";

export function failoverDesired(rows: LbIpRow[]): string[] {
  if (rows.length === 0) return [];
  const live = rows.filter((r) => isPoolMember(r.health));
  const pool = live.length > 0 ? live : rows;
  const sorted = [...pool].sort(
    (a, b) => a.priority - b.priority || a.weight - b.weight,
  );
  const minPriority = sorted[0]!.priority;
  const primaries = sorted.filter((r) => r.priority === minPriority);
  if (live.length > 0) {
    return primaries.map((r) => r.ip);
  }
  return [sorted[0]!.ip];
}