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On 03/24/2014 12:47 PM, Jan Safranek wrote:
I'm injecting the old "Fedora Server Role D-BUS API Design
Discussion" thread as I was not subscribed at that time... I looked
at the API and I have few remarks:
First, don't use under_scores, DBus prefers CamelCase.
Noted. I hate CamelCase, but I'll bow to the convention.
> /org/fedoraproject/server/ServerRoleManager: * properties: *
> all_roles: list of object references to Roles that can be
> installed and deployed * staging_roles: list of object references
> to Roles that have been pre-loaded but not yet configured *
> active_roles: list of object references to deployed Roles *
> version: API version * methods:
It would be nice if there was e.g.
/org/fedoraproject/server/ServerRole object with
org.freedesktop.DBus.ObjectManager interface, which would list all
objects provided by the service. That's how DBus works usually. It
may make 'all_roles', 'staging_roles' and 'active_roles'
properties of ServerRoleManager irrelevant, as an application can
easily list all object + filter out those with appropriate
Good idea. As noted, I'm not tremendously familiar with D-BUS
interfaces and I'm learning as I go. That does sound like a useful way
to present the objects.
> /org/fedoraproject/server/role/$ROLE: * properties: * version:
> API version * loaded: Bool: whether the packages are
> installed * deployed: Bool: whether the Role has been
> deployed * methods: * PreloadRole: Install all necessary
> software packages for default operation * GetFirewallPorts: list
> of port/protocol pairs that the Role needs open in the firewall *
> PrepBackup: method to invoke any necessary pre-backup
> steps (such as running a database dump to a file) *
> GetBackupFiles: list of filesystem path objects that
> identifies all data that should be copied by backup software
> # Individual Roles should have unique implementations of
> installation # and deployment
> e.g. /org/fedoraproject/server/role/DomainController * methods: *
> DeployPrimaryDomainController: Set up the first domain controller
> in the domain. * DeployReplicaDomainController: Add a new replica
> domain controller to the domain * AddCertificateAuthority:
> Add a certificate authority to this domain controller *
> EnableDisableDNS: Enable or disable the DNS server
> on this server
I am not sure if DBus supports inheritance. I have seen only
single object implementing multiple interfaces, i.e.
/org/fedoraproject/Server/Role/DomainController would implement
both, org.fedoraproject.Server.Role.Generic [or so] and
org.fedoraproject.Server.Role.DomainController, each with distinct
properties and methods.
In this situation, I was thinking of inheritance more from a
conceptual rather than implementation view. I meant that a consumer
should be able to assume that certain standard methods (with known
On the implementation side, I was using inheritance in my
quick-n-dirty dbus-python service to accomplish that.
And most importantly, there must be some sort of job management. I
guess installing role packages and deploying a role are long
running operations in general. In this case, the
DeployPrimaryDomainController() method should return a reference to
a new object with Job interface, which: - can be watched for
progress [i.e. Cockpit draws a nice progress bar] - reports any
error messages [Cockpit shows an error alert]
- with possibility to cancel the job if such functionality is
needed and feasible.
This may be harder to accomplish, unless we build in snapshotting
capabilities. A lot of deployment-type activities would be difficult
to abort and restore to the original state. But I suppose if the role
supports it, certainly good to have.
There may be more than one running jobs, started by [in theory]
different Cockpit users, so all needs to be robust enough e.g. to
queue jobs and execute them serially.
As consequence, simple boolean for Role.Generic.loaded and
.deployed may not be enough, some 'in progress' would be nice.
I am afraid it's not _that_ simple DBus service as initially
planned. It's not particularly difficult either, it just needs a
good design. And the API should be reviewed by someone who really
understands DBus and knows its design patterns, so it fits well
there. I am certainly not an expert here, I just have played a bit
with few services like UDisks and storaged and I can spot only the
most obvious issues.
I fully admit to not being that person, hence why this is a public
Thank you very much for your feedback. It's very helpful.
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