So I developed a system with Nest.js which is able to create a dynamic cronjob from a user's input in the frontend application, I store this data in my database and at the same time I create the job in the server with the Dynamic schedule module API. Today I was wondering what would happen to my cronjobs if my server was shutdown or if it restarted itself, since my jobs aren't declarative and they are created at runtime I think that maybe when my server starts I should create the cronjobs again? I'm not sure if this get stored in memory or something since it's not in the documentation.
My concern, in fewer words, is:
Should I recreate my jobs using the information from the database once the server starts itself? Why yes or why not?
Once the server restarts, you'll have to restart your CRON tasks.
The reason for this is that your NestJS application is not really adding CRON expressions to a crontab on the machine but instead scheduling and running these tasks in a CRON expression capable task runner (package example: node-cron)
Once the server stops, the scheduler (that runs on the same process) also stops.
You've mentioned you already store the tasks in a database, so you should be able to get the information you need to recreate the task on server init.
I assume you have a Service that handles CRON tasks and has access to the DB. Otherwise you can just create a dedicated one
You can modify it to implement the OnModuleInit interface and execute logic that would read all the existing tasks that should run and start them:
@Injectable()
class CronService implements OnModuleInit {
constructor(private readonly cronRepository: CronRepository) {}
/*
...
CRON IMPLEMENTATION
...
*/
private async restartSavedCronTasks(): Promise<void> {
// get data from DB and start all relevant tasks
}
async onModuleInit: Promise<void> {
await this.restartSavedCronTasks();
}
}