Introduce `timeout` in dynamic pollsters sub-system

This patch introduces a new option for the dynamic pollsters'
sub-system to define the request timeout for requests executed
by the dynamic pollsters. The default timeout value will be 30
seconds. If it (the timeout option) is set to `None`, this means
that the request never times out on the client-side. Therefore,
one might have problems if the server never closes the connection.
The pollsters are executed serially, one after the other; if the
request hangs, all pollsters (including the non-dynamic ones) will
stop executing.

This option is being introduced after a failure that we had when
using the dynamic pollsters; one of the APIs did not respond, and the
server did not close the connection of the request, which made
Ceilometer dynamic pollsters stop gathering data. To avoid such a
situation, we recommend the community review and merge this patch.

Change-Id: I4735f20d75d329ccafc797fe285d9fef579f593e

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/source/admin/telemetry-dynamic-pollster.rst b/doc/source/admin/telemetry-dynamic-pollster.rst
index 12999c6c..9a321cb6 100644
--- a/doc/source/admin/telemetry-dynamic-pollster.rst
+++ b/doc/source/admin/telemetry-dynamic-pollster.rst
@@ -190,6 +190,14 @@ attributes to define a dynamic pollster:
     headers:
       "x-openstack-nova-api-version": "2.46"
 
+*  ``timeout``: optional parameter. Defines the request timeout for the
+   requests executed by the dynamic pollsters to gather data. The default
+   timeout value is 30 seconds. If it is set to `None`, this means that the
+   request never times out on the client side. Therefore, one might have
+   problems if the server never closes the connection. The pollsters are
+   executed serially, one after the other. Therefore, if the request hangs,
+   all pollsters (including the non-dynamic ones) will stop executing.
+
 The complete YAML configuration to gather data from Magnum (that has been used
 as an example) is the following: