Download CloudWatch Logs by TypeScript and AWS SDK

download_cloudwatch_logs.ts

import {
  CloudWatchLogsClient,
  DescribeLogGroupsCommand,
  DescribeLogStreamsCommand,
  GetLogEventsCommand,
} from "@aws-sdk/client-cloudwatch-logs";
import { fromIni } from "@aws-sdk/credential-provider-ini";
import * as date from "date-fns";
import fs from "fs";

// Parameters
const profile = "default";

const logGroupNameIncludes = ["Group1"];
const logGroupNameIndex = 0;
const logStreamNameIndex = 0;

const start = "05-08 06:20";
const addHours = 1;

const out = "log.txt";

// Logics
const startDate = date.parse(start, "MM-dd HH:mm", new Date());
const startNum = date.getTime(startDate);
const endDate = date.add(startDate, { hours: addHours });
const endNum = date.getTime(endDate);
console.log(
  `Download duration: ${date.formatISO(startDate)} - ${date.formatISO(endDate)}`
);

async function findLogGroupName(client: CloudWatchLogsClient) {
  let counts = 0;
  let nextToken: string | undefined = undefined;
  for (;;) {
    const command: DescribeLogGroupsCommand = new DescribeLogGroupsCommand({
      nextToken,
    });
    const res = await client.send(command);
    // console.log(res.logGroups!);
    const names = res
      .logGroups!.filter((lg) =>
        logGroupNameIncludes.every((s) => lg.logGroupName!.includes(s))
      )
      .map((lg) => lg.logGroupName!);
    if (counts + names.length > logGroupNameIndex) {
      const lgn = names[logGroupNameIndex - counts];
      return lgn;
    } else {
      counts += names.length;
    }
    if (res.nextToken) {
      nextToken = res.nextToken;
    } else {
      return undefined;
    }
  }
}

async function findLogStream(client: CloudWatchLogsClient, name: string) {
  let counts = 0;
  let nextToken: string | undefined = undefined;
  for (;;) {
    const command: DescribeLogStreamsCommand = new DescribeLogStreamsCommand({
      logGroupName: name,
      orderBy: "LastEventTime",
      descending: true,
      nextToken,
    });
    const res = await client.send(command);
    const streams = res.logStreams!;
    // console.log(streams);
    if (counts + streams.length > logStreamNameIndex) {
      const s = streams[logStreamNameIndex - counts];
      return s;
    } else {
      counts += streams.length;
    }
    if (res.nextToken) {
      nextToken = res.nextToken;
    } else {
      return undefined;
    }
  }
}

async function saveLogEvents(
  client: CloudWatchLogsClient,
  logGroupName: string,
  logStream: string
) {
  const fd = await fs.promises.open(out, "w+");
  let nextToken: string | undefined = undefined;
  for (;;) {
    const command: GetLogEventsCommand = new GetLogEventsCommand({
      logGroupName,
      logStreamName: logStream,
      startFromHead: true,
      startTime: startNum,
      endTime: endNum,
      nextToken,
    });
    const res = await client.send(command);
    // console.log(res.events);
    res.events!.forEach((e) => fd.write(e.message!));
    if (nextToken === res.nextForwardToken) {
      break;
    } else {
      nextToken = res.nextForwardToken;
    }
  }
}

(async () => {
  const client = new CloudWatchLogsClient({
    credentials: fromIni({ profile }),
  });
  const logGroupName = await findLogGroupName(client);
  if (!logGroupName) {
    console.error("log group name not found");
    process.exit(1);
  }
  console.log(`logGroupName: ${logGroupName}`);
  const logStream = await findLogStream(client, logGroupName);
  if (!logStream) {
    console.error("log stream not found");
    process.exit(1);
  }
  console.log(`logStream: ${logStream.logStreamName!}`);
  console.log(
    `logStream duration: ${date.formatISO(logStream.firstEventTimestamp!)} ${date.formatISO(
      logStream.lastEventTimestamp!
    )}`
  );
  await saveLogEvents(client, logGroupName, logStream.logStreamName!);
})();

package.json

{
  "name": "cloudwatch-logs-downloader",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "ts-node download_cloudwatch_logs.ts"
  },
  "author": "Takeshi Horiuchi",
  "license": "MIT",
  "dependencies": {
    "@aws-sdk/client-cloudwatch-logs": "^3.36.1",
    "@aws-sdk/credential-provider-ini": "^3.36.1",
    "date-fns": "^2.25.0",
    "ts-node": "^10.3.0"
  }
}