S3 read-after-update consistency

s3.ts

import { writeS3Obj, getS3FileAsObj, listObjects, deleteS3Files } from "./S3";

/**
 * S3 does not provide read-after-update consistency.
 * It does provide read-after-firstWrite consistency (as long as no GET has been requested)
 * We write a new file every time it changes, and we read the latest file.
 * S3 guarantees list of files are sorted in ascending UTF-8 Binary Order
 *
 */

const cleanUp = async (key: string) => {
  const response = await listObjects({
    MaxKeys: 1000,
    Bucket: process.env.BUCKET_NAME!,
    Prefix: key,
  });
  const keys = response.Contents?.map((c) => c.Key!) || [];
  await deleteS3Files(keys.slice(0, keys.length - 1));
};

export const writeServiceState = async (key: string, state: any) => {
  await writeS3Obj(`${key}.${Date.now()}`, state);
  await cleanUp(key);
};
export const getServiceState = async (key: string, defaultVal: T): Promise => {
  const response = await listObjects({
    MaxKeys: 1000,
    Bucket: process.env.BUCKET_NAME!,
    Prefix: key,
  });
  if (!response.Contents || response.Contents.length === 0) {
    console.log("No state file for key " + key);
    return defaultVal;
  }

  return getS3FileAsObj(response.Contents[response.Contents.length - 1].Key!);
};