So lets think about a practical example. We want to expose a REST
service that is visible to the inside via its direct url on the server
that exposes the service and also via a proxy server where this service
will have a different url.
So the server side topology manager would detect that the service is to
be published. It would call the distribution provider to export the service.
The provider would then return two ExportRegistrations one for the
direct access and one for the access over the proxy. They could each
have a special property like "zone" to distinguish them (like "backend"
and "frontend").
The TopologyManager on the front end client side then could be
configured to only consider Endpoints that have (zone=frontend) for imports.
I think on the client I like this approach. It would also need only
minimal additions to the TopologyManager code. We would either need a
config setting for a import filter or a SPI where the user can supply
custom filtering logic.
On the server side I am not so sure. The distribution provider would
need to know about the proxy and it might even need to communicate with
it to get the alias address for the service it exports. Another problem
is that in such a scenario the server administrator would be able to
poke new holes into the firewall.
On the positive side I agree that the DistributionProvider might know
more about the details of the protocol to be qualified to create a
suitable address than the TopologyManager.
Generally I think I would prefer a more central approach where you have
a system that is part of the firewall that manages which services to
expose to the outside world. Maybe this can also be done with Remote
Service Admin.
How about this:
See http://liquid-reality.de/display/liquid/Zones+for+Aries+RSA
We use a system with two instances of the zookeeper discovery. One that
communicates with the backend zookeeper and one that communicates with
the frontend zookeeper.
The backend discovery would report all internal services to the
TopologyManager. The TopologyManager would select the backend services
for import using a special proxy DistributionProvider.
The proxy DistributionProvider would create an OSGi service with the
necessary prorperties to be exported as a proxy for the frontend. The
TopologyManager would detect this service and export it using the same
proxy DistributionProvider which would create an ExportRegistration with
the url of the proxy Endpoint it would also either implement an HTTP
Proxy for the service or configure an external proxy server.
This approach might even be able to cover both cases the case where we
have one zookeeper with all addresses and the case where we have
spearate zookeepers for frontend and backend.
If I understand correctly then the Endpoint information for the proxy
service would always be sent to all discovery providers, or can the
TopologyManager select where to export it? If it can not then I think we
would need a filtering config for the zookeeper discovery so the
frontend zookeeper will only contain the frontend services and the
backend zookeeper would only contain the backend services.
What do you think?
Christian
On 21.09.2016 11:49, Timothy Ward wrote:
Hi Christian,
From an RSA perspective this is a Topology Management issue, not a discovery
issue. Services should be exposed by the Distribution Provider with multiple
ExportRegistrations (and hence multiple EndpointDescriptions), one for the
“internal” URL and one for the “proxied” URL The Topology Manager on the client
side should then import the Endpoint Description that gives the behaviour that
it desires.
Using multiple discovery services to do this sort of scoping is possible, but
much more complicated than controlling it using the Topology Manager. Adding a
simple filter to the client side’s Topology Manager’s EndpointEventListener
would probably be sufficient, and could be done easily using Config Admin.
Regards,
Tim
On 19 Sep 2016, at 13:52, Christian Schneider <[email protected]> wrote:
I just had a discussion with Panu Hämäläinen about the DiscoveryPlugin
mechanism.
See https://issues.apache.org/jira/browse/ARIES-1613 and
https://issues.apache.org/jira/browse/ARIES-1614 .
What he needs is to have two zones of services, a backend zone and a frontend
zone.
The (or some) services in the backend will be published with http. Inside the
backend zone the services should be available using this http url.
In the frontend zone these services should also be visible but their url should
point to a proxy server that offer a https connection and potentially some
additional security mechanisms.
So we can not simply have one (zookeeper or other) discovery view. Instead we
need a different discovery view for backend and frontend and some mechanism to
make some services from one zone available in the other while also applying
some changes like pointing to a proxy.
Do you think it makes sense to support this case in Aries RSA in some way?
I thought we might also be able to interact with one of the existing proxy
servers to automatically register the proxy for each service. Such a mechanism
is very typically for cloud enabled architectures. So that might also bring us
nearer to good cloud support.
I would be happy about any ideas and feedback.
Christian
--
Christian Schneider
http://www.liquid-reality.de
Open Source Architect
http://www.talend.com
--
Christian Schneider
http://www.liquid-reality.de
Open Source Architect
http://www.talend.com
