Supervisor with Quantum Elixir Cron Job - cron

Question

Forgive me if I don't understand elixir really well as I am new to it...
I'm using quantum-elixir as a cron api to dynamically create cron jobs. When someone POSTS to a route I save the cron job details into my Ecto Repo and then simultaneously create a quantum job with Quantum.add_job.
In development when I close my server and restart it, i have to re-add all my cron jobs because they don't survive through a restart. So that got me thinking that if my application were to crash that would make me lose all the cron jobs. (I'm thinking about of scenarios where I host the app on Google compute engine and for whatever reason need to do a reset on the compute instance, ie upgrades on the box, etc.)
So I was wondering what the appropriate way to restart my app is while keeping these cron jobs?
Right now I have the following:
worker(Task,[MyApp.RebootTask, :reboot, []], restart: :transient)
in the start function of my application module.
Is this the right approach? What other considerations do I need to factor in?
Any guidance is greatly appreciated

Answer 1

I query my db and create a list with the job definition of every item
%Quantum.Job{
name: job_name,
overlap: false,
run_strategy: %Quantum.RunStrategy.Random{nodes: :cluster},
schedule: Crontab.CronExpression.Parser.parse!(schedule),
task: task,
state: :active,
timezone: "Europe/Zurich"
}
To have the jobs started at application startup, I do something like this
defmodule Alerts.Scheduler do
use Quantum.Scheduler, otp_app: :alerts
require Logger
#environmet_blacklist [:test]
def init(opts) do
case Enum.member?(#environmet_blacklist, Mix.env()) or IEx.started?() do
true ->
IO.inspect(opts)
opts
false ->
delete_all_jobs()
opts_with_jobs = get_startup_config(opts)
opts_with_jobs |> IO.inspect()
opts_with_jobs
end
end
def get_startup_config(opts) do
job_definition = Alerts.Business.Alerts.get_all_alert_jobs_config()
(opts |> List.delete(List.keyfind(opts, :jobs, 0))) ++ [jobs: job_definition]
end
In my application start
def start(_type, _args) do
[
Alerts.Repo,
AlertsWeb.Endpoint |> supervisor([]),
if(System.get_env() != :test, do: Alerts.Scheduler),
Alerts.VersionSupervisor |> supervisor([])
]
|> Supervisor.start_link(strategy: :one_for_one, name: Alerts.Supervisor)
end

Answer 2

It doesn't look like Quantum persists dynamically-added cronjobs, since the more typical approach is to define your cronjobs (named or otherwise) in your config.exs.
Since you're already storing the job details with Ecto, it's just a matter of reading those details and readding them when your application starts. Since you're already using Quantum, the following in config/config.exs ought to do the trick:
config :quantum, cron: [
"#reboot": &MyApp.some_function_to_read_and_readd_my_cronjobs/0
]