Lambda Warm Pools: Low-Latency Backends for Coding Agent Tools

// cdk/agent-tools.ts
import * as lambda from "aws-cdk-lib/aws-lambda";
import * as appscaling from "aws-cdk-lib/aws-applicationautoscaling";

const fn = new lambda.Function(this, "AgentToolSearch", {
  runtime: lambda.Runtime.NODEJS_20_X,
  memorySize: 1024,
  timeout: Duration.seconds(30),
  // lean init — see cold-start hygiene below
});

const alias = fn.addAlias("live");
const target = alias.addAutoScaling({ minCapacity: 0, maxCapacity: 20 });

// ✅ Weekday eng hours Asia/Kolkata 09:00–21:00 ≈ 03:30–15:30 UTC
target.scaleOnSchedule("workday-on", {
  schedule: appscaling.Schedule.cron({ minute: "30", hour: "3", weekDay: "MON-FRI" }),
  minCapacity: 5,
});
target.scaleOnSchedule("workday-off", {
  schedule: appscaling.Schedule.cron({ minute: "30", hour: "15", weekDay: "MON-FRI" }),
  minCapacity: 0,
});

// ❌ Eager heavy imports in top-level
import { HugeSdk } from "huge-sdk";
const client = new HugeSdk();

// ✅ Lazy inside handler paths you actually hit
export async function handler(event: Event) {
  const { HugeSdk } = await import("huge-sdk");
  const client = new HugeSdk();
  return client.search(event.query);
}

# illustrative — cap account spend on provisioned concurrency
aws cloudwatch put-metric-alarm \
  --alarm-name agent-pcu-spend \
  --metric-name ProvisionedConcurrencyUtilization \
  --threshold 0.2 \
  --comparison-operator LessThanThreshold \
  # low utilization → shrink schedule