Promise is a key element to make sure your service is running as expected. This HowTo will explain how to add a new promise in the context of html5as-base software release.

Here is the commit introducing this functionality to html5as Software release: commit diff.

Add a section for a monitoring promise in instance instance_html5as.cfg.in. We choose to add a [port-listening-promise] to check that the nginx service is listening port. It doesn't check if the service return an error or not.

# Port Listening checking promise
[port-listening-promise]
<= monitor-promise-base
promise = check_socket_listening
name = nginx-port-listening.py
config-host = ${html5as:ip}
config-port = ${html5as:port}

Add port-listening-promise section to the list of processed parts in instance_html5as.cfg.in as no other processed parts depend on it.

[buildout]
parts =
    ...
    port-listening-promise
    ...

Refer How To Move to md5sum automatic update to update md5sum:

$ cd ~/srv/project/slapos/software/html5as-base
$ ../../update-hash

To inspect the output of slapos node software:

$ slapos node software --all

To inspect the output of slapos node instance:

$ slapos node instance --all

Observe the log of slapos node Instance. It now contains the promise info at the end:

2021-10-27 03:01:23 slapos[86186] INFO Checking slappart0 promises...
2021-10-27 03:01:23 slapos[86186] INFO Checking promise nginx-port-listening.py...
2021-10-27 03:01:23 nginx-port-listening.py[86186] INFO socket connection OK ('2001:67c:1254:f1::7692', 8086, 0, 0)

If you face issues, please update your local branch first: 
$ git stash
$ git fetch
$ git reset --hard origin/master
$ git stash pop

Then rerun the past commands