Re: [systemd-devel] How to specify dynamic services/requirements
Thanks Jérémy, That was what I needed. I was afraid to be headed to the wrong way. Now that I know what to do, I need to know where and when. > you could create a template (xendomains@.service) and use drop-ins to do > per-instance overrides > (/etc/systemd/system/xendomains@vm1.service.d/append.conf) > that would allow you to individualize each domain while keeping the common > parts > > I would find a way to prevent a domain with no corresponding to start > (maybe by not defining a mandatory key in the template) to make sure no > rogue domains are created... > I would use a template like xendomains@.service in order to specify common stuff. However, the config of which vm are enabled (autostart) is only available at boot time. Is a systemd generator the way to go? Is is there another way to define it? Also, should I use a service patch (like append.conf you mentioned) or simply directly create /run/.../xendomains@vm1.service? It would be trivial to define a template xendomains@.service and start services like "systemctl start xendomains@vm1.service", that would read /etc/xen/vm/vm1 and launch it. I just don't know how I could define dynamic dependency for that instance depending on the content of /etc/xen/vm/vm1. Execstartpre can check requirements and prevent a service to run but not wait for a resource to be available. It would be something like ExecRequires=. Instances seems to be created only when asked directly (systemctl start xendomains@vm1.service), which might be triggered by something like udev event. Is there anything like ExecListStartInstances=, ExecListRunningInstances=? Generators can create something like that but they are triggered only at boot and daemon-reload. It would be interesting to somehow run "something like generators" when start/stop/status is called. >From what I know about systemd, I'm thinking of something like a generator that will create services for all autostart and saved vm. The current script-based xendomains.service will run after all xendomains@.service instances. This way, a new enabled-after-boot vm would be started with "systemctl restart xendomains". I could use the existence of /etc/xen/auto/vm or /var/lib/xen/save/vm as requirement for xendomains@vm.service, in order to avoid to start a disabled-after-boot vm. However, this does not look like an elegant solution. Regards, > -- Luiz Angelo Daros de Luca luizl...@gmail.com ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
[systemd-devel] How to specify dynamic services/requirements
Hello, I'm facing a problem with Xen machines that depends on MD devices. As I'm new to systemd world, I might not be seeing the clean solution. That's why I'm asking for an advice. MD devices are automatically detect by udev. If device state is safe, /dev/md/myraid is started. However, if the state is not safe (like a raid with a missing disk), udev starts mdadm-last-resort@.timer that tries to start the device anyway after 30s. As mdadm-last-resort conflicts with the device presence, it will not run if the required disk appears before 30s. Even with mdadm-last-resort running, MD device might still be usable, although degraded. Xen VM are started by xendomains.service, that simply calls a shell script like in SysV times. It start a bunch of VM in sequence. xendomains.service has only generic dependencies that let it run at a very early stage. Now the problem: If for any reason, a MD device takes some seconds to appear (or even 30s as the last resort), xendomains will fail to start any machine that depends on that MD device. I'm extending manually xendomains.service to depend on a series of MD devices, that fixed the start order problem. However, I created new problems. First I had to frequently regenerate those "Requires" as machines are frequently started/migrated between hosts (I also consider using systemd generators). But worse, whenever a single MD device permanently fails, xendomains is never started and all those VM that does not use the failed MD never start. I though that maybe I could use instances (xendomains@vm1.service) to launch VM individually, each of them depending on those devices it uses. However, these instances would have to be dynamically generated based on its configuration (systemd generators from /etc/xen/vm/xxx.cfg?), either on boot, shutdown or simply periodically. The stop procedure will still be the same, calling the SysV script as systemd will not know about VM (re)started after boot. I even though about simply create an alternative xendomains.service that does not depend on any MD device and launch it using a systemd timer if the xendomains that depends on MD devices isn't started after 30s. It looks ugly but it might work. Regards, -- Luiz Angelo Daros de Luca luizl...@gmail.com ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
