The Docker Image includes a health check with the following options:
--interval=30s
Specifies the time interval to run the health check.
In this case, the health check is performed every 30 seconds.
--timeout=10s
Specifies the amount of time to wait for a response from the "HEALTHCHECK" command.
If the response does not arrive within 10 seconds, the health check fails.
--start-period=5s
Specifies the amount of time to wait before starting the health check process.
In this case, the health check process will begin 5 seconds after the container is started.
--retries=3
Specifies the number of times Docker should retry the health check
before considering the container to be unhealthy.
The CMD instruction is used to define the command that will be run as part of the health check.
In this case, the command is wget --quiet --tries=1 --spider http://localhost:3000/ || exit 1.
This command will attempt to connect to http://localhost:3000/
and if it fails it will exit with a status code of 1.
If this command returns a status code other than 0, the health check fails.
Overall, this "HEALTHCHECK" instruction is defining a health check process
that runs every 30 seconds, and waits up to 10 seconds for a response,
begins 5 seconds after the container is started, and retries up to 3 times. \
The health check attempts to connect to http://localhost:3000/
and will considers the container unhealthy if unable to connect.