Changes between Initial Version and Version 1 of ServiceProviderFederation/CLARIN IdP/AnyCast

Timestamp:

03/17/14 10:53:54 (10 years ago)

Author:

Dieter Van Uytvanck

Comment:

--

ServiceProviderFederation/CLARIN IdP/AnyCast

@@ +1 @@
+You asked me for some infos on our use of [http://en.wikipedia.org/wiki/Anycast AnyCast] for
+load-balancing/automatic failover. I gave a presentation on that many
+years ago and things still work the same way:
+
+http://www.switch.ch/aai/support/presentations/infoday-2005/AAI-ID05-50-SWITCHwayf.pdf
+
+We are using an approach that is very similar to the one described here:
+
+https://www.usenix.org/legacy/events/lisa10/tech/full_papers/Weiden.pdf
+
+Basically, we have two instances, one in Zurich, one in Lausanne.
+Both of them have a unique IP but they also have share a common Anycast
+IPD via a local interface:
+{{{
+lo:0      Link encap:Local Loopback
+          inet addr:130.59.31.249  Mask:255.255.255.255
+          UP LOOPBACK RUNNING  MTU:16436  Metric:1
+}}}
+
+The interface lo:0 is bound to the anycast IP (130.59.31.249)
+
+On both instances there is the routing daemon Quagga installed. Quagga
+announces the root to lo:0 to its neighbour routers. If lo:0 is disabled
+(ifdown lo:0), quagga stops announcing the route of that instance, which
+means that all requests go the other instance. This is good for maintenance.
+
+Normally, both instances are active and receive requests (one a bit more
+than the other). If an instance has a power loss or network disruption,
+the routing daemon fails to announce the route to the anycast daemon.
+Within a few seconds (I think 3s or 4s) the route to that instance is
+deleted from the routers in our network thanks to the OSPF dead timer.
+This then is part of the automatic failover.
+
+As the presentation explains, we also have some monitoring in place to
+ensure the host is available. One local monitoring script also will
+withdraw the route to the local instance if the web server is not
+running properly or the response is not containing a specific response.
+In such a case, the script executes the "ifdown lo:0".