The compose file references the image docker.internal:5000/monit:latest that does not exist publicly because the image was built using the provided monit Dockerfile.

The /conf mount within the guest should be mapped to a folder on the host and it will be read by monit on startup. Ideally, a small settings file should be present with the following contents:

set daemon 120            # check services at 2-minute intervals
set logfile /dev/stdout
set httpd port 2812
    use address 0.0.0.0
    allow admin:swordfish
include services/*

that:

• sets monit on a two minute timer,
• the log file is redirected to stdout such that it can be observable from docker,
• the HTTP access port is set to 2812 and the HTTP server listens on all addresses (necessary for Docker) with the username admin and password swordfish,
• finally, monit is instructed to load all the service files from the services/ subfolder from the current directory where the user can place monit services to monitor.