Please review and comment on the following proposal
to add support for service discovery in inetd. Please
provide your comments preferably by eod Friday 2/2.
Thanks,
Rishi
Service discovery support in inetd
Background:
Multicast DNS (mDNS) is an extension to the DNS protocol to perform DNS
operations on the local-link using multicast. Multicast DNS also
supports DNS operations to discover and advertise network services on
the network (as specified in the DNS-SD Internet draft). The service
discovery component of the NWAM project will integrate the framework and
tools from the Apple "Bonjour" project to allow applications to
advertise and discover network services using Multicast DNS on Solaris.
Part of the framework includes the mDNS daemon service performing the
DNS operations and a public service discovery library: libdns_sd(3LIB)
for applications to register and advertise services by issuing requests
to the mDNS daemon. As part of this proposal the inetd SMF delegated
restarter will utilize the service discovery framework and provide
support to advertise services on Solaris.
Proposal:
This proposal adds service discovery support in inetd(1M), an SMF
delegated restarter, to advertise services on the network using mDNS. By
adding this support in the inetd restarter, all services managed by
inetd both currently and in the future can utilize the support and
advertise the service on the local link. We propose to modify the ftp
and telnet services to utilize this support in inetd first. When ftp or
telnet service is enabled inetd will use the mDNS service on Solaris to
advertise the service on the network. inetd connects to the mDNS daemon
via IPC using unix domain sockets. If the connection to the mDNS daemon
fails inetd periodically tries to connect to the mDNS service and
advertise the service.
The inetd restarter advertises the service name, transport protocol
(TCP/UDP) and port number of services that have turned on service
advertisement option. The service name is the application name stored in
the 'inetd/name' service property. The application name also is used to
lookup the service port number to advertise from the /etc/services file
(or another source in nsswitch.conf for the services database). In the
future we could add a new property to customize the advertised service
name.
No other information is advertised by the inetd restarter and the
advertisement is restricted to the local link only. In the future a
service property for inetd managed services can be introduced to provide
the inetd restarter with any additional information about the service to
advertise. For example an audio streaming service could additionally
advertise information about the stream such as the audio codec. inetd
controlled services using 'rpc' transport are not advertised via mDNS.
DNS-SD Internet draft requires the transport protocol of the service to
be either TCP or UDP.
Administration & Configuration:
To enable/disable service advertisement of an inetd managed service
using mDNS, administrators should use the inetadm(1M) tool to modify the
value of the new service advertised property: 'inetd/advertised'. The
new boolean property 'advertised' in the property group 'inetd' is
introduced by this proposed work for services controlled by the inetd
restarter. The new property indicates whether the service should be
advertised using mDNS. The property value is of type boolean and is
false by default. inetadm(1M) will be updated to support modifying and
listing this new property. ftp and telnet services will have the
property set to 'true'. Setting the property to 'true' does not
guarantee the service is advertised. The mDNS service on Solaris must be
enabled and online before services on the machine are advertised. Any
inetd.conf(4) entries converted by inetconv(1M) to SMF services have the
service advertised property value initially set to 'false'.
SMF service dependencies:
Integrating this feature in the inetd SMF delegated restarter
does not add a dependency between the new mdns service
(svc:/network/mdns:default) and inetd (svc:/network/inetd:default).
inetd managed services wishing to advertise using mDNS should not
add the mdns service as a dependency. A dependency is not needed,
because disabling the mDNS service on the system does not affect the
functionality of inetd or inetd managed applications advertised using
mDNS.
The inetd controlled service is advertised by the inetd restarter only
when the target service is online. When the advertised service goes
offline/disabled the inetd restarter ends the advertisement. If the mDNS
service is offline/disabled the inetd restarter periodically tries to
successfully connect to the mDNS service before issuing new inet service
advertisement requests.
Usage example:
The following example shows how users can advertise an inetd controlled
service on the network:
# Advertising an inetd controlled service using mDNS
> svcadm enable vnc
> inetadm -m svc:/network/vnc:default advertised=true
> svcadm refresh svc:/network/vnc:default
# Verifying the advertisement. Browsing for "vnc" service types on the
local link.
> dns-sd -B _vnc._tcp local.
Browsing for _vnc._tcp.local.
Timestamp A/R Flags if Domain Service Type Instance Name
16:32:43.343 Add 2 2 local. _vnc._tcp. whitestar1-a
# Looking up the service instance returns host and port information.
> dns-sd -L whitestar1-a _vnc._tcp local.
Lookup waltair._vnc._tcp.local.
16:34:18.705 whitestar1-a._vnc._tcp.local. can be reached at
whitestar1-a.local.:5900
Future work: The master SMF restarter svc.startd(1M) could also be
updated to support advertising network services using mDNS. There are
currently no plans to add service discovery support in the master
SMF restarter. Additional properties could be introduced for inetd
controlled services to customize the advertised service name and to
advertise additional information about the service.
Open question: Considering the above future work to include this support
in the master SMF restarter and new properties introduced to customize
the service advertisement is it better to create the 'advertised'
property under a new property group 'mdns' that is not specific to a
restarter?
References:
* www.apple.com/bonjour
* www.dns-sd.org
* www.multicastdns.org
