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@mangosteen/background-healthcheck

v1.3.0

Published

Healthcheck for containerized background tasks

Downloads

141

Readme

background-healthcheck

Node.js package designed to provide healthchecking to containerized background tasks.

Installation

With npm do:

$ npm install @mangosteen/background-healthcheck

Then, create a file healthcheck.js:

import { healthcheck } from '@mangosteen/background-healthcheck';

healthcheck(10000).then(process.exit);

And configure your Dockerfile:

HEALTHCHECK --interval=15s --retries=3 --timeout=5s \
    CMD ["node", "healthcheck.js"]

If you use AWS ECS, then keep in mind ECS ignores Dockerfile's HEALTHCHECK. You need to put the healthcheck command in task definition. Similarly, Kubernetes ignores Dockerfile's HEALTHCHECK too, and provides an alternative way to check health. However, you can use our library in either case.

Usage in your task's code

The healthcheck process checks if the heartbeat has been signaled recently. If you do not call the signalHeartbeat periodically, the healthcheck will report your container as unhealthy. Pay special attention to async functions that take a long time to complete.

You can customize the heartbeat period using staleInterval param of the healthcheck function. If you signal heartbeat less often than staleInterval, the container will be unhealthy.

import { signalHeartbeat } from '@mangosteen/background-healthcheck';

for (let i = 0; i < 1000; i++) {
    await insertRowsBatchToDb();
    await signalHeartbeat();
}

If you are processing streams in a pipeline, you can also signal heartbeat automatically as chunks are processed using createHeartbeatStream transform stream:

import { createHeartbeatStream } from '@mangosteen/background-healthcheck';
import stream from 'stream';
import fs from 'fs';
import { promisify } from 'util';
const pipeline = promisify(stream.pipeline);

(async () => {
    await pipeline(
        fs.createReadStream('./shakespeare.txt'),
        createHeartbeatStream({ interval: 2000 }),
        createSinkStream(),
    );
})();

function createSinkStream(): stream.Writable {
    return new stream.Writable({
        highWaterMark: 0,
        write(chunk, _encoding, callback): void {
            callback();
        },
    });
}

What is it good for?

Imagine running a Docker task in AWS Elastic Container Service, on EC2 or Fargate. This task is not a server, but rather a data retrieval / transformation task. It loads data from some data source (like an API or a DB), manipulates it in some way (maybe resizes an image?), then writes the result somewhere. Wouldn't it be nice to still be able to determine if such a container is healthy? That's what this package is for.

Reference