CODEWITHSUNDEEP
timergogoji
shardnit
shardnit

Reputation: 137

How to recover Go timer from web-server restart (or code refresh/upgrade)?

Consider a web service, for instance, where user can make an API request to start a task at certain scheduled time. Task definition and scheduled time are persisted in a database. First approach I came up with is to start a Go timer and wait for the timer to expire in a Goroutine (not blocking the request). This goroutine, after time expiration, will also fire another API request to start executing the task.

Now the problem arises when this service is redeployed. For zero downtime deployment I am using Einhorn with goji. After code reload, obviously both timer goroutine and timer-expiration-handler goroutine dies. Is there any way to recover Go timer after code reload?

Another problem I am struggling with is to allow the user to interrupt the timer (once its started). Go timer has Stop to facilitate this. But since this is a stateless API, when the \interrupt request comes in service doesn't have context of timer channel. And it seems its not possible to marshal the channel (returned from NewTimer) to disk/db.

Its also very well possible that I am not looking at the problem from correct perspective. Any suggestions would be highly appreciated.

Upvotes: 0

Views: 245

Answers (1)

OneOfOne
OneOfOne

Reputation: 99351

One approach that's commonly used is to schedule the task outside your app, for example using crontab or systemd timers.

For example using crontab:

# run every 30 minutes
*/30 * * * * /usr/bin/curl --head http://localhost/cron?key=something-to-verify-local-job >/dev/null 2>&1

Using an external task queue is also a valid option like @Not_a_Golfer mentioned but more complicated.

Upvotes: 1

Related Questions