Re: "primary" Condition for drbd?

[Andrei Borzenkov <arvidjaar@xxxxxxxxx>]

On Thu, Jun 13, 2024 at 12:27 PM Harald Dunkel <harald.dunkel@xxxxxxxxxx> wrote:
>
> I missed to mention, drbdadm does know:
>
>         # drbdadm role space
>         Primary/Secondary
>
> meaning "space" is primary on this host. You can also look
> at /proc/drbd:
>
>         # cat /proc/drbd
>         version: 8.4.11 (api:1/proto:86-101)
>         srcversion: 19D914EA50F713FCCE48607
>
>          1: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
>             ns:4044664 nr:0 dw:4044664 dr:726481 al:188 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
>          2: cs:Connected ro:Secondary/Primary ds:UpToDate/UpToDate C r-----
>             ns:0 nr:2228224 dw:2228224 dr:0 al:0 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
>          3: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
>             ns:699492 nr:0 dw:699492 dr:266197 al:75 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
>
> Problem is, it doesn't say "/dev/drbd1". "space" and "1" are
> defined in drbd's config files, mapping it to "/dev/drbd1". To
> evaluate the condition you have to perform a pretty complex
> task.
>
> Does systemd allow to run a program to evaluate a custom
> condition in a unit file? Maybe I am too blind to see, but
> I haven't found it mentioned on https://www.freedesktop.org/\
> software/systemd/man/latest/systemd.unit.html.
>
> The context is: I want to mount/activate /dev/drbd1, if it is
> primary. (If it is not, then /dev/drbd1 should be silently
> ignored.) Next I want to start the LXC containers provided by
> the virtual block device, and setup networking and storage
> accordingly. The same should happen for /dev/dbrd{2..n}.
>
> Maybe this is beyond the scope of systemd.
>

What you are looking for is the pacemaker.