Lambda X-Ray Sampling: Cost Versus Debuggability During Incidents

{
 "rule_name": "checkout-baseline",
 "priority": 1000,
 "fixed_target": 1,
 "rate": 0.05,
 "service_name": "checkout-api",
 "service_type": "*",
 "host": "*",
 "http_method": "*",
 "url_path": "*",
 "resource_arn": "*",
 "attributes": {}
}

{
 "rule_name": "checkout-incident-boost",
 "priority": 10,
 "fixed_target": 100,
 "rate": 1.0,
 "service_name": "checkout-api",
 "resource_arn": "arn:aws:lambda:REGION:ACCT:function:checkout-api"
}

import { SSM } from "@aws-sdk/client-ssm";
import { XRay } from "@aws-sdk/client-xray";

export async function beginIncidentTraceBoost(fn: string, ttlMinutes = 60) {
 const until = new Date(Date.now() + ttlMinutes * 60_000).toISOString();
 await new SSM({}).putParameter({
 Name: `/tracing/boost/${fn}`,
 Value: until,
 Type: "String",
 Overwrite: true,
 });
 // Upsert high-priority sampling rule via XRay PutSamplingRules / console-as-code
}

export async function samplingRateFor(fn: string, baseline = 0.05): Promise<number> {
 try {
 const p = await new SSM({}).getParameter({ Name: `/tracing/boost/${fn}` });
 if (p.Parameter?.Value && Date.parse(p.Parameter.Value) > Date.now()) return 1;
 } catch { /* no boost */ }
 return baseline;
}