Nats self publish a scheduled cron message?

[NOT-HAL9000]

I'm looking to publish a message to a stream at a certain interval.

I can set up a cron job and publish a message, however I'm wondering if it's possible (or planned) to be able to schedule a message to have the nats server self publish messages at set intervals? Basically a light implementation of cron jobs on top of jetstream.

Thanks

[derekcollison]

At this time you will need to figure out a way to publish yourself.

We have had folks use TTL of a stream with max deliver of 1 and advisory for when the message can no longer be delivered, but this seems contrived at the moment.

[drewcorlin1]

Would it work to do the following?

• Have an ackWait that is the difference between time of publishing and the desired delivery time
• On delivery 1 (using redelivery count) ignore the message and don't ack it.
• On delivery 2 actually do whatever you want to with the message.

[derekcollison]

Yes, that could work.

[ashupednekar]

Here's a POC based on this approach

https://github.com/ashupednekar/natshed

[Zetanova]

Beside KV, a managed job scheduler would be a great addition to nats.
It is nearly always required to also track job success / failure beside the response messages.

[jnmoyne]

You may want to take a look at https://github.com/choria-io/asyncjobs

[Zetanova]

yes, something like it, but without following:

• requires a separate process for the supervisor
• It uses the simple request/reply pattern. It breaks the NATS request/reply-many to _INBOX pattern.

Of course can the scheduling be done with an external protocol/process,
but it is a very basic feature for post applications like the KV store.

I only search for something basic like:

• schedule job A with message P in 10min to subject X.Y.Z NATS will then send this message in >10min to the subject as a Request/Reply but with a special durable _INBOX (Inbox on JS) and tagged with Job headers
• subscribe on job Athis will dequeue all response message (one or more) from the durable _INBOX tagged with Job headers
• get jobs regular request to get the status of current jobs

[tamis-laan]

Something like this would be sooooo helpful:

ns = await nats.connect("localhost:4222")

ns.cron.schedule("my_periodic_task_id", "*/1 * * * *", "my_topic",  "my message".encode())

ns.cron.schedule("my_one-shot_task_id", "2025-04-20T18:40:00+02:00", "my_topic",  "my message".encode())

ns.cron.remove("my_periodic_task_id")

When these tasks are one shot they should be automatically be removed after triggering and sending their message to the target topic.