CP-51870: Refresh toolstack services

[liulinC]

• varstored-guard Before: xenopsd.servcie->xenopsd-xc.service
• Remove unnecessary xenopsd services
  • xenopsd
  • xenopsd-xenlight
  • xenopsd-simulator
  • xenopsd-libvirt
• Reorder services to stop/start
  • forkexecd: does not depends on others, move to last
  • xenopsd-xc After xcp-rrdd. so it needs after xcp-rrdd-*

Note: the for loop reverse the TO_RESTART order

[robhoes]

The odd thing about xe-toolstack-restart is that is stops and starts services in the same order, whereas it'd better do the restarts in the opposite order. Otherwise you can't really reason about dependencies at all...

Even better may be to have a single "toolstack" service that depends on all of these individual services and restart just that, hoping that systemd would stop and start them things correctly based on dependencies encoded in the service files (as a single systemctl stop x y z command ignores those dependencies).

[robhoes]

Also, your branch is out of date, and you are missing some new rrdd plugins.

[liulinC]

The odd thing about xe-toolstack-restart is that is stops and starts services in the same order, whereas it'd better do the restarts in the opposite order. Otherwise you can't really reason about dependencies at all...

Even better may be to have a single "toolstack" service that depends on all of these individual services and restart just that, hoping that systemd would stop and start them things correctly based on dependencies encoded in the service files (as a single systemctl stop x y z command ignores those dependencies).

It looks systemd can figure out the right order to start the service, so start order does not matter.
However, the stop order matters if the dependent service stop before others.

Yeah, one toolstack service configure the depends, and just let systemd decide the order sounds a better solution.

[lindig]

Converted this to draft. This needs to be thought trough and brought up to date before it will be considered for merging. My preference would be for start and restart the sequence being controlled by systemd but this requires testing that dependencies are correct.

[liulinC]

Converted this to draft. This needs to be thought trough and brought up to date before it will be considered for merging. My preference would be for start and restart the sequence being controlled by systemd but this requires testing that dependencies are correct.

Yeah, I am considering how to use systemd to manage it and got a roughly plan.
I will update this PR later.

[liulinC]

test result refer to xapi.spec repo pull request.

[lindig]

Toolstack restart is exercised quite a bit in tests. So I would hope that this would find problems.

[liulinC]

Toolstack restart is exercised quite a bit in tests. So I would hope that this would find problems.

Yes, XenRT detect a problem so I update Requires -> Wants , otherwise, systemctl restart /stop xcp-rrdd in some case would restart/stop xapi.

[robhoes]

The change to use a systemd target looks great, thanks for doing it. As discussed elsewhere, it would be better to include the target file in this repo.

Otherwise, I think a difference between old and the new may be that if any of the services fail to start, now xe-toolstack-restart would not raise an error? At least that is how Wants is defined, so that would be the case for systemctl start toolstack.target. However, the docs for PartOf say that it is similar to Requires (but as a one-way dependency), so does systemctl restart toolstack.target raises an error if any of the contained services fail to start?

[liulinC]

The change to use a systemd target looks great, thanks for doing it. As discussed elsewhere, it would be better to include the target file in this repo.

Otherwise, I think a difference between old and the new may be that if any of the services fail to start, now xe-toolstack-restart would not raise an error? At least that is how Wants is defined, so that would be the case for systemctl start toolstack.target. However, the docs for PartOf say that it is similar to Requires (but as a one-way dependency), so does systemctl restart toolstack.target raises an error if any of the contained services fail to start?

This is very good question and catch.

According to my check, systemctl restart toolstack.target does not raise error, so I write a following up check and raise any failures.