如何在 k8s 中复制的 pod 中拥有只执行一次的逻辑（一段代码）？

Question

I have a cronjob which is inside my golang application code. now, this code is inside a container which is inside a pod

What happens :
Suppose I have a cronjob to send emails every Sunday.
The application starts to run and the cronjobs are created as soon as the application starts.
Now, If I have 3 such pods, the applications starts thrice in each pod and would have it's own cronjob, so the emails will be sent three times.

What I want :
The email should be sent only once ie all cronjobs should run only once independent of how many replicas I create

How can I achieve this?
Preferably: I would like to have the jobs inside the application because if I separate them out, I will have to call the API endpoint instead of the service directly.

Answer 1

TL;DR: Perhaps you need to rethink the value of co-locating the cronjobs with the function exposed via the API.

ie put the cronjobs in a separate pod with no replicas.

From the information available, that would seem to solve your problem most easily.

The question then arises, what value was gained or problem solved ( other than convenience) by co-locating the cronjobs in the first place?

If there was no other problem, or that problem is more easily solved in other ways than the additional complexity involved in solving the problem that the co-location solution has created , then you have your answer.

Another test to apply would be which solution architecture would be easier for someone to understand (and in the future extend, modify or maintain):

1. separate cronjobs, running only once, and doing their work via an API

2. multiple cronjobs seemingly intentionally placed in a replicaset but with some complex coordination mechanism that contrives to ensure that of these multiple jobs only one instance is actually effective and the others rendered essentially inoperative