Elixir standalone script in a Linux cron

Questions / Help
1

Hello,

Is there a way I can write an elixir script and schedule it in a Linux cron job to perform some repetitive tasks?

I would like the script to invoke some Ecto functions from modules defined inside an Elixir mix project.

Any help would be most appreciated.

Thanks.

Jerry

1 Like
2

Hi,
here is a nice article on using Elixir as a scripting language…
https://thoughtbot.com/blog/is-elixir-a-scripting-language
Enjoy :slight_smile:

1 Like
3

Hi @sweeneydavidj,

Thanks for your response.

I had read and tried the steps outlined in the guide ealier before my post here.
Below is the error I get when I attempt to run the standalone script with mix:

13:06:27.160 [error] Failed to start Ranch listener Test.Router.HTTP in :ranch_tcp:listen([cacerts: :…, key: :…, cert: :…, port: 80, ip: {0, 0, 0, 0}]) for reason :eaddrinuse (address already in use)

13:06:27.180 [info] Application test exited: Test.Application.start(:normal, []) returned an error: shutdown: failed to start child: {:ranch_listener_sup, Test.Router.HTTP}
** (EXIT) shutdown: failed to start child: :ranch_acceptors_sup
** (EXIT) {:listen_error, Test.Router.HTTP, :eaddrinuse}
** (Mix) Could not start application test: Test.Application.start(:normal, []) returned an error: shutdown: failed to start child: {:ranch_listener_sup, Test.Router.HTTP}
** (EXIT) shutdown: failed to start child: :ranch_acceptors_sup
** (EXIT) {:listen_error, Test.Router.HTTP, :eaddrinuse}

4

Your cron seems to want to start the application a second time, rather than to communicate with it, therefore ranch can’t boot, as the port it wants to listen on, is already in use by your main instance of the application.

If you use distillery just use a custom task, if you are using 1.9-releases, use their equivalent, if you use mix (as a command via cron) then make sure to use --no-start (IIRC), if you use an escript make sure it does not start the application and its dependencies, but just loads them.

2 Likes
5

Hello @NobbZ,

Thanks for the response.
It worked for me.

I, however, have another issue still pertaining to this same activity.
When the function that has been invoked by the standalone script from a module in the main project has some Ecto processes to run,
I get the error below:

** (ArgumentError) repo Test.Repo is not started, please ensure it is part of your supervision tree
lib/ecto/query/planner.ex:148: Ecto.Query.Planner.query_lookup/6
lib/ecto/query/planner.ex:131: Ecto.Query.Planner.query_with_cache/7
lib/ecto/repo/queryable.ex:124: Ecto.Repo.Queryable.execute/5
lib/ecto/repo/queryable.ex:37: Ecto.Repo.Queryable.all/4
lib/test/transactions.ex:387: Test.Transaction.process_staged_requests/0
scripts/staged_requests.exs:5: (module)

I would be grateful once again for your assistance.

Thanks.

Jerry

6

Well, you need to start your ecto repository without the rest of the application.

Be aware that it might then crash as well, as dependencies for ecto might be missing.

To be honest, the easiest thing is probably to use quantum and trigger the task from within your application.

2 Likes
7

Thanks very much, @NobbZ.

I’ll go ahead and use Quantum instead.

Regards,

Jerry