Topology Collection Strategies
There are mainly two ways of collecting topology information:
FETCH strategy
RECEIVE strategy
Each Topology instance has a strategy field which can be set to
the desired setting.
FETCH Strategy
Topology data will be fetched from a URL.
When some links are not detected anymore they will be flagged as "down" straightaway.
RECEIVE Strategy
Topology data is sent directly from one or more nodes of the network.
The collector waits to receive data in the payload of a POST HTTP request;
when such a request is received, a key parameter it's first checked
against the Topology key.
If the request is authorized the collector proceeds to update the topology.
If the data is sent from one node only, it's highly advised to set the
expiration_time of the Topology instance to 0 (seconds), this
way the system works just like in the FETCH strategy, with the only
difference that the data is sent by one node instead of fetched by the
collector.
If the data is sent from multiple nodes, you SHOULD set the
expiration_time of the Topology instance to a value slightly
higher than the interval used by nodes to send the topology, this way
links will be flagged as "down" only if they haven't been detected for a
while. This mechanism allows to visualize the topology even if the network
has been split in several parts, the disadvantage is that it will take a
bit more time to detect links that go offline.