During Rolling Update both old and new Spec tasks

[Deepak-Vohra]

Description

During a rolling update tasks from both the new service Spec and the old service Spec are running, albeit for a short while. Is a rolling update designed as such? If a rolling update is to update a MySQL database image to a Postgres image, would both databases be served during an update?

A design issue, does not require detailed info for test.

"Before Swarm updates all of the tasks, you can see that some are running redis:3.0.6 while others are running redis:3.0.7. "
https://docs.docker.com/engine/swarm/swarm-tutorial/rolling-update/

[thaJeztah]

Yes, it's possible both an MySQL and PostgreSQL server would be running during the update. I don't think such a scenario would be very realistic though.

There's a number of options available to pick the right update strategy for your situation, that can be set by the user; https://github.com/docker/docker-ce/blob/17.07/components/cli/docs/reference/commandline/service_update.md

      --update-delay duration              Delay between updates (ns|us|ms|s|m|h)
      --update-failure-action string       Action on update failure ("pause"|"continue"|"rollback")
      --update-max-failure-ratio float     Failure rate to tolerate during an update
      --update-monitor duration            Duration after each task update to monitor for failure (ns|us|ms|s|m|h)
      --update-order string                Update order ("start-first"|"stop-first")
      --update-parallelism uint            Maximum number of tasks updated simultaneously (0 to update all at once)

Other strategies could be a blue/green deployment using multiple services, for example as explained in https://github.com/stevvooe/sillyproxy

[Deepak-Vohra]

The update options are not implemented, at least not for a rolling update on Docker for AWS. On rolling update a one replica service to 5 replicas first a few new tasks are started and subsequently the first task is shutdown even though the default --update-order is "stop-first". Does some other criterion override --update-order?

[thaJeztah]

If you suspect there's a bug it would be helpful to provide the exact steps to reproduce the issue and the output of docker version and docker info

[Deepak-Vohra]

Isn't at least one service task expected to be running in a rolling update for high availability of a service?

[thaJeztah]

Let me close this ticket for now, as it looks like it went stale.