Convert an ECS task definition into a dot env file

taskdef-to-env.ts

import {
  GetSecretValueCommand,
  SecretsManagerClient,
} from '@aws-sdk/client-secrets-manager';
import fs from 'fs';
import path from 'path';

// usage npx tsx taskdef-to-env.ts path/to/ecs/task-definition.json
// outputs: /path/to/ecs/.env.local
// expects aws to be configured (see aws-vault)

const client = new SecretsManagerClient();

const taskDefPath: string = process.argv[2];
const dotEnvPath: string = path.join(path.dirname(taskDefPath), '.env.local');

async function getSecretFromValueFrom(valueFrom: string) {
  let secretId = valueFrom;
  let jsonKey: string | boolean = false;

  if (valueFrom.endsWith('::')) {
    // json key references end in ::
    const [arn, aws, secretsmanager, region, accountId, secret, shortId, _jsonKey /* :: */] = valueFrom.split(':');
    secretId = [arn, aws, secretsmanager, region, accountId, secret, shortId].join(':');
    jsonKey = _jsonKey;
  }

  const command = new GetSecretValueCommand({
    SecretId: secretId
  });
  const response = await client.send(command);
  const raw = response.SecretString

  if (raw === undefined) {
    throw new Error(`Secret ${secretId} has no value`);
  }

  if (!jsonKey) { return raw; }

  const json = JSON.parse(raw);
  return json[jsonKey];
}

async function main() {
  console.log('fetching', taskDefPath, 'to', dotEnvPath);

  const json = fs.readFileSync(taskDefPath);
  const task = JSON.parse(json.toString());

  const envs: { name: string, value: string }[] = task.containerDefinitions[0].environment;

  const secretRefs: { name: string, valueFrom: string }[] = task.containerDefinitions[0].secrets;
  const secrets = await Promise.all(secretRefs.map(async (s: any) => {
    const value = await getSecretFromValueFrom(s.valueFrom);
    return { name: s.name, value };
  }));

  const dotEnv: string[] = [];
  envs.forEach((e) => dotEnv.push(`${e.name}=${e.value}`));
  secrets.forEach((s) => dotEnv.push(`${s.name}=${s.value}`));

  fs.writeFileSync(dotEnvPath, dotEnv.join('\n'));
}

main().catch((err) => {
  console.error('unhandled exception', err);
  process.exit(1);
});