Author: stefanegli
Date: Tue Nov 3 10:42:40 2015
New Revision: 1712247
URL: http://svn.apache.org/viewvc?rev=1712247&view=rev
Log:
SLING-4831 : Clarify topology connectors are cross-cluster, not intra-cluster
Modified:
sling/site/trunk/content/documentation/bundles/discovery-api-and-impl.mdtext
Modified:
sling/site/trunk/content/documentation/bundles/discovery-api-and-impl.mdtext
URL:
http://svn.apache.org/viewvc/sling/site/trunk/content/documentation/bundles/discovery-api-and-impl.mdtext?rev=1712247&r1=1712246&r2=1712247&view=diff
==============================================================================
---
sling/site/trunk/content/documentation/bundles/discovery-api-and-impl.mdtext
(original)
+++
sling/site/trunk/content/documentation/bundles/discovery-api-and-impl.mdtext
Tue Nov 3 10:42:40 2015
@@ -118,10 +118,28 @@ Administrative note: All the information
/var/discovery/impl
-### Connectors
+### Topology Connectors for Cross-Cluster Discovery
-The "cross-cluster" announcement is done via HTTP(s) heartbeats between
(arbitrary) cluster instances. These HTTP heartbeats
-(internally termed `connectors`) are configured at
[/system/console/configMgr/org.apache.sling.discovery.impl.Config][1].
+From a discovery API's point of view a cluster consists of all instances that
are connected to the same repository.
+The above described built-in mechanism of storing a lastHeartbeat property
into the (shared) repository, of voting on changes
+and creating an explicit establishedView results in automatic discovery within
a cluster. There is therefore
+no further configuration needed for discovering instances in the same cluster.
+
+However, for discovering multiple clusters such an automatic discovery is not
possible and the clusters need
+to be explicitly configured using (cross-cluster) topology connectors:
+
+A topology connector is a periodically issued HTTP PUT that announces the part
of the topology known to the
+sending instance to the receiving instance and vica-verca the receiving
instance announces its part of the
+topology to the sender in the response of the very same HTTP PUT. This way
whatever other clusters are connected
+to sender or receiver will be made known to each other. Such a 'topology
announcement' will be valid either until
+the same sender sends the announcement again (which it does periodically) - or
until it times out (configurable).
+A topology connector is by definition always between clusters, never within
the same cluster. Topology connectors
+can be structured in an arbitrary way (chain, star, tree, etc) with the only
important point to note here that
+since changes in the topology propagate through these topology connectors they
have a certain delay (namely
+the configured heartbeatInterval per hop).
+
+Topology connectors are configured at
[/system/console/configMgr/org.apache.sling.discovery.impl.Config][1].
+They use the same interval and timeout as the repository heartbeats
(heartbeatInterval and heartbeatTimeout).
### WebConsole
@@ -171,4 +189,4 @@ The following properties can be configur
[1]:
http://localhost:8888/system/console/configMgr/org.apache.sling.discovery.impl.Config
- [2]: http://localhost:8888/system/console/topology
\ No newline at end of file
+ [2]: http://localhost:8888/system/console/topology
