1.6 KiB
Efficient polling with the changes-since parameter
The REST API allows you to poll for the status of certain operations
by performing a GET on various elements. Rather than
re-downloading and re-parsing the full status at each polling interval,
your REST client may use the changes-since parameter to
check for changes since a previous request.
The changes-since time is specified as an ISO 8601 dateTime
(2011-01-24T17:08Z). The form for the timestamp is
CCYY-MM-DDThh:mm:ss. An optional time zone may be
written in by appending the form ±hh:mm which describes the timezone as
an offset from UTC. When the timezone is not specified
(2011-01-24T17:08), the UTC timezone is assumed.
If nothing has changed since the changes-since time, an
empty list is returned. If data has changed, only the items changed
since the specified time are returned in the response. For example,
performing a GET against:
https://api.servers.openstack.org/v2.1/servers?changes-since=2015-01-24T17:08Zwould list all servers that have changed since Mon, 24 Jan 2015 17:08:00 UTC.
To allow clients to keep track of changes, the
changes-since filter displays items that have been
recently deleted. Both images and servers contain a
DELETED status that indicates that the resource has been
removed. Implementations are not required to keep track of deleted
resources indefinitely, so sending a changes-since time in
the distant past may miss deletions.