feat: add cheapest-region pricing mode for aws perf harness

Author: sqdshguy

docs/BENCHMARK.md

@@ -80,12 +80,14 @@ If you do not want to benchmark on your laptop/network, use the AWS CLI harness:
 
 Note: the runner clones from `origin` by default, so both refs must exist in the remote repository (push your branch/commit first if needed).
 Default region is `us-west-2`; pass `--region <aws-region>` to override.
+Use `--cheapest-region` to auto-pick the cheapest on-demand region for your selected instance type.
 
 The script:
 
 - Launches a short-lived EC2 instance with SSM (no inbound SSH required).
 - Runs the same benchmark scenarios for `--base-ref` and `--head-ref` on the same host.
 - Produces `tmp/aws-perf/<run-id>/summary.json` with per-scenario deltas and a pass/fail gate.
+- Produces `tmp/aws-perf/<run-id>/pricing.json` with on-demand and recent spot pricing info.
 - Terminates the instance automatically unless `--keep-instance` is passed.
 
 Useful options:
@@ -94,6 +96,13 @@ Useful options:
 - `--instance-type c6i.large` (default) for low cost and stable throughput.
 - `--threshold-pct 5` to set the regression gate.
 - `--scenarios 'wreq.session.get.small;wreq.session.get.4kb;wreq.isolated.get.small'` to limit scope.
+- `--cheapest-region` to choose the cheapest on-demand region automatically.
+
+Pricing-only check (no EC2 launch):
+
+```bash
+./scripts/aws-perf/ec2-compare.sh --instance-type c6i.large --cheapest-region --pricing-only
+```
 
 Safety cleanup:
 

scripts/aws-perf/ec2-compare.sh

@@ -13,6 +13,8 @@ DEFAULT_REGION="us-west-2"
 REGION="${AWS_REGION:-${AWS_DEFAULT_REGION:-$DEFAULT_REGION}}"
 INSTANCE_PROFILE_NAME="wreq-js-perf-ssm-profile"
 INSTANCE_TYPE="c6i.large"
+AUTO_CHEAPEST_REGION=false
+PRICING_ONLY=false
 USE_SPOT=true
 FALLBACK_ON_DEMAND=true
 SUBNET_ID=""
@@ -28,13 +30,16 @@ WARMUP=2
 CONCURRENCY=8
 SCENARIOS="wreq.session.get.small;wreq.transport.get.small;wreq.session.get.4kb;wreq.session.post.32b;wreq.isolated.get.small;node.fetch.get.small"
 OUTPUT_DIR="$ROOT_DIR/tmp/aws-perf/$RUN_ID"
+PRICING_JSON=""
+CHEAPEST_REPORT_PATH=""
 
 usage() {
   cat <<'EOF'
 Usage: scripts/aws-perf/ec2-compare.sh [options]
 
 Options:
   --region <aws-region>             AWS region (default: us-west-2)
+  --cheapest-region                 Auto-select cheapest on-demand region for instance type
   --instance-profile <name>         IAM instance profile with AmazonSSMManagedInstanceCore
   --instance-type <type>            EC2 instance type (default: c6i.large)
   --subnet-id <subnet-id>           Optional; auto-detected when omitted
@@ -50,6 +55,7 @@ Options:
   --threshold-pct <n>               Throughput drop threshold for regression (default: 5)
   --ttl-hours <n>                   Auto-expiry tag horizon (default: 2)
   --output-dir <path>               Local output directory
+  --pricing-only                    Print pricing info and exit without launching EC2
   --on-demand                        Disable Spot and use on-demand instance
   --no-fallback-on-demand            Do not retry on-demand when Spot launch fails
   --keep-instance                    Do not terminate instance after run
@@ -92,7 +98,111 @@ base64_encode_file() {
   fi
 }
 
+pricing_script_path() {
+  printf '%s/pricing-info.mjs' "$SCRIPT_DIR"
+}
+
+resolve_cheapest_region() {
+  local pricing_script="$1"
+  local report_path="$2"
+
+  node "$pricing_script" --instance-type "$INSTANCE_TYPE" --region "$REGION" --cheapest >"$report_path"
+
+  local cheapest_region
+  cheapest_region="$(node - "$report_path" <<'NODE'
+const fs = require("node:fs");
+const report = JSON.parse(fs.readFileSync(process.argv[2], "utf8"));
+process.stdout.write(report.cheapestOnDemand?.regionCode || "");
+NODE
+)"
+
+  [[ -n "$cheapest_region" ]] || fail "Unable to determine cheapest region for instance type: $INSTANCE_TYPE"
+
+  local cheapest_details
+  cheapest_details="$(node - "$report_path" <<'NODE'
+const fs = require("node:fs");
+const report = JSON.parse(fs.readFileSync(process.argv[2], "utf8"));
+const cheapest = report.cheapestOnDemand;
+if (!cheapest) {
+  process.exit(1);
+}
+const usd = Number(cheapest.usdPerHour);
+const rate = Number.isFinite(usd) ? usd.toFixed(4) : "n/a";
+process.stdout.write(`${cheapest.regionCode}|${cheapest.location || "unknown"}|${rate}`);
+NODE
+)"
+
+  local cheapest_code cheapest_location cheapest_rate
+  IFS='|' read -r cheapest_code cheapest_location cheapest_rate <<<"$cheapest_details"
+  log "Cheapest on-demand region for $INSTANCE_TYPE: $cheapest_code ($cheapest_location) at \$$cheapest_rate/hour"
+  REGION="$cheapest_region"
+}
+
+collect_pricing_report() {
+  local pricing_script="$1"
+  local report_path="$2"
+  node "$pricing_script" --instance-type "$INSTANCE_TYPE" --region "$REGION" >"$report_path"
+}
+
+merge_pricing_reports() {
+  local selected_path="$1"
+  local cheapest_path="$2"
+  node - "$selected_path" "$cheapest_path" <<'NODE'
+const fs = require("node:fs");
+const selectedPath = process.argv[2];
+const cheapestPath = process.argv[3];
+
+const selected = JSON.parse(fs.readFileSync(selectedPath, "utf8"));
+const cheapest = JSON.parse(fs.readFileSync(cheapestPath, "utf8"));
+
+selected.cheapestOnDemand = cheapest.cheapestOnDemand || null;
+selected.topOnDemand = cheapest.topOnDemand || [];
+selected.regionCountSampled = cheapest.regionCountSampled || 0;
+
+fs.writeFileSync(selectedPath, JSON.stringify(selected, null, 2));
+NODE
+}
+
+print_pricing_summary() {
+  local report_path="$1"
+  while IFS= read -r line; do
+    log "$line"
+  done < <(
+    node - "$report_path" <<'NODE'
+const fs = require("node:fs");
+const report = JSON.parse(fs.readFileSync(process.argv[2], "utf8"));
+
+const onDemand = report.selectedOnDemand;
+if (onDemand) {
+  console.log(
+    `Pricing selected region: ${onDemand.regionCode} (${onDemand.location || "unknown"}) at $${Number(onDemand.usdPerHour).toFixed(4)}/hour on-demand`,
+  );
+} else {
+  console.log(`Pricing selected region: ${report.selectedRegion} (on-demand price unavailable)`);
+}
+
+const spot = report.selectedSpot24h;
+if (spot) {
+  console.log(
+    `Spot (last ${spot.windowHours}h): avg $${Number(spot.avgUsdPerHour).toFixed(4)}/hour, min $${Number(spot.minUsdPerHour).toFixed(4)}, max $${Number(spot.maxUsdPerHour).toFixed(4)}, samples ${spot.samples}`,
+  );
+}
+
+if (report.cheapestOnDemand) {
+  const c = report.cheapestOnDemand;
+  console.log(
+    `Cheapest on-demand sampled: ${c.regionCode} (${c.location || "unknown"}) at $${Number(c.usdPerHour).toFixed(4)}/hour`,
+  );
+}
+NODE
+  )
+}
+
 cleanup() {
+  if [[ -n "$CHEAPEST_REPORT_PATH" ]]; then
+    rm -f "$CHEAPEST_REPORT_PATH" || true
+  fi
+
   if [[ -n "$PARAMS_FILE" ]]; then
     rm -f "$PARAMS_FILE" || true
   fi
@@ -107,6 +217,7 @@ trap cleanup EXIT INT TERM
 while [[ $# -gt 0 ]]; do
   case "$1" in
     --region) REGION="$2"; shift 2 ;;
+    --cheapest-region) AUTO_CHEAPEST_REGION=true; shift ;;
     --instance-profile) INSTANCE_PROFILE_NAME="$2"; shift 2 ;;
     --instance-type) INSTANCE_TYPE="$2"; shift 2 ;;
     --subnet-id) SUBNET_ID="$2"; shift 2 ;;
@@ -122,6 +233,7 @@ while [[ $# -gt 0 ]]; do
     --threshold-pct) THRESHOLD_PCT="$2"; shift 2 ;;
     --ttl-hours) TTL_HOURS="$2"; shift 2 ;;
     --output-dir) OUTPUT_DIR="$2"; shift 2 ;;
+    --pricing-only) PRICING_ONLY=true; shift ;;
     --on-demand) USE_SPOT=false; shift ;;
     --no-fallback-on-demand) FALLBACK_ON_DEMAND=false; shift ;;
     --keep-instance) SHOULD_CLEANUP=false; shift ;;
@@ -138,8 +250,38 @@ requires mktemp
 requires node
 
 [[ -n "$REGION" ]] || fail "AWS region is required (use --region or set AWS_REGION)"
+[[ -n "$INSTANCE_TYPE" ]] || fail "Instance type is required"
+
+if [[ "$AUTO_CHEAPEST_REGION" == true ]] && [[ -n "$SUBNET_ID" || -n "$SECURITY_GROUP_ID" ]]; then
+  fail "--cheapest-region cannot be combined with --subnet-id or --security-group-id"
+fi
 
 mkdir -p "$OUTPUT_DIR"
+PRICING_JSON="$OUTPUT_DIR/pricing.json"
+
+PRICING_SCRIPT="$(pricing_script_path)"
+[[ -f "$PRICING_SCRIPT" ]] || fail "Missing pricing helper script: $PRICING_SCRIPT"
+
+if [[ "$AUTO_CHEAPEST_REGION" == true ]]; then
+  CHEAPEST_REPORT_PATH="$(mktemp)"
+  log "Detecting cheapest on-demand region for instance type: $INSTANCE_TYPE"
+  resolve_cheapest_region "$PRICING_SCRIPT" "$CHEAPEST_REPORT_PATH"
+fi
+
+collect_pricing_report "$PRICING_SCRIPT" "$PRICING_JSON"
+
+if [[ -n "$CHEAPEST_REPORT_PATH" ]]; then
+  merge_pricing_reports "$PRICING_JSON" "$CHEAPEST_REPORT_PATH"
+  rm -f "$CHEAPEST_REPORT_PATH" || true
+fi
+
+print_pricing_summary "$PRICING_JSON"
+log "Pricing report: $PRICING_JSON"
+
+if [[ "$PRICING_ONLY" == true ]]; then
+  log "Pricing-only mode enabled; exiting without launching EC2"
+  exit 0
+fi
 
 log "Resolving refs"
 BASE_REF="$(git -C "$ROOT_DIR" rev-parse "$BASE_REF")"