Health check

Consider this line described in the dockerfile

COPY ./healthcheck.sh ./
COPY ./healthcheck.js ./
HEALTHCHECK CMD /opt/orbs/healthcheck.sh

• The ORBS-NODE orchestrator runs this process in order to determine if your ORBS-VM instance is healthy.

• A common method used by the Orbs Network's services, including ORBS-VMs, to determine a container's health, is to access its /op/orbs/status/status.json (explained in detail here) and make sure it is not stale (i.e., that it hasn't been updated in recent few minutes).

HEALTHCHECK is mandatory for your docker container to run on the Orbs Guardian nodes. Do not skip the following instructions.

HEALTHCHECK example

For example, let's write a simple check based on the existence of a status.json and its "uptime" field's recency.

1. Create healthechek.sh (sibling to Dockerfile) shell file containing the following:

#!/bin/sh
node ./healthcheck.js

As long as the execution of this batch returns status code 0, the container is healthy.

2. create healthecheck.js file with the following health implementations:

const fs = require('fs');

try {
  // read json file to JS Object
  const status = JSON.parse(fs.readFileSync('./status/status.json').toString());

  // check how many seconds ago since the file was written
  const updatedAgoSeconds = (new Date().getTime() - new Date(status.Timestamp).getTime()) / 1000;
  
  // return error in case it hasn't been written in the last 5 minutes
  if (updatedAgoSeconds > 5 * 60) {
    console.log(`Timestamp was not updated in status.json for ${updatedAgoSeconds} seconds.`);
    process.exit(128);
  }
} catch (err) {
  // exception throws in the following cases:
  // - status/status.json does not exist
  // - status/status.json does not follow expected json format
  console.log(err.stack);
  process.exit(0); // don't restart in this case, maybe service isn't ready
}
// all good
process.exit(0);

3. Install HEALTHCHECK In dockerfile

...
# install healthcheck based on status.json
COPY ./healthcheck.sh ./
COPY ./healthcheck.js ./
HEALTHCHECK CMD /opt/orbs/healthcheck.sh
...

4. Build your docker file - now your VM is good to go on Orbs v3!

Please notice that the healthcheck in the example, relays on your VM to write a valid json file to ./status/status.json in the container/ read more about this here

The legacy orbs-v2 service installation spec can be found here