[ClusterLabs] how to connect to the cluster from a docker container

Jan Pokorný jpokorny at redhat.com
Tue Aug 6 08:03:59 EDT 2019

On 06/08/19 13:36 +0200, Jan Pokorný wrote:
> On 06/08/19 10:37 +0200, Dejan Muhamedagic wrote:
>> Hawk runs in a docker container on one of the cluster nodes (the
>> nodes run Debian and apparently it's rather difficult to install
>> hawk on a non-SUSE distribution, hence docker). Now, how to
>> connect to the cluster? Hawk uses the pacemaker command line
>> tools such as cibadmin. I have a vague recollection that there is
>> a way to connect over tcp/ip, but, if that is so, I cannot find
>> any documentation about it.
> I think that what you are after is one of:
> 1. have docker runtime for the particular container have the abstract
>    Unix sockets shared from the host (--network=host? don't remember
>    exactly)
>    - apparently, this weak style of compartmentalization comes with
>      many drawbacks, so you may be facing hefty work of cutting any
>      other interferences stemming from pre-chrooting assumptions of
>      what is a singleton on the system, incl. sockets etc.
> 2. use modern enough libqb (v1.0.2+) and use
>      touch /etc/libqb/force-filesystem-sockets
>    on both host and within the container (assuming those two locations
>    are fully disjoint, i.e., not an overlay-based reuse), you should
>    then be able to share the respective reified sockets simply by
>    sharing the pertaining directory (normally /var/run it seems)
>    - if indeed a directory as generic as /var/run is involved,
>      it may also lead to unexpected interferences, so the more
>      minimalistic the container is, the better I think
>      (or you can recompile libqb and play with path mapping
>      in container configuration to achieve smoother plug-in)

Oh, and there's additional prerequisite for both to at least
theoretically work -- 1:1 sharing of /dev/shm (which may also
be problematic in a sense).

> Then, pacemaker utilities would hopefully work across the container
> boundaries just as if they were fully native, hence hawk shall as
> well.
> Let us know how far you'll get and where we can colletively join you
> in your attempts, I don't think we had such experience disseminated
> here.  I know for sure I haven't ever tried this in practice, some
> one else here could have.  Also, there may be a lot of fun with various
> Linux Security Modules like SELinux.

Jan (Poki)
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