Some applications require Congress to be highly available. Some applications require a Congress Policy Engine (PE) to handle a high volume of queries. This guide describes Congress support for High Availability (HA) High Throughput (HT) deployment.
Please see the OpenStack High Availability Guide for details on how to install and configure OpenStack for High Availability.
Warm Standby is when a software component is installed and available on the secondary node. The secondary node is up and running. In the case of a failure on the primary node, the software component is started on the secondary node. This process is usually automated using a cluster manager. Data is regularly mirrored to the secondary system using disk based replication or shared disk. This generally provides a recovery time of a few minutes.
In this method, both the primary and secondary systems are active and processing requests in parallel. Data replication happens through software capabilities and would be bi-directional. This generally provides a recovery time that is instantaneous.
Congress provides Active-Active for the Policy Engine and Warm Standby for the Datasource Drivers.
Run N instances of the Congress Policy Engine in active-active configuration, so both the primary and secondary systems are active and processing requests in parallel.
One Datasource Driver (DSD) per physical datasource, publishing data on oslo-messaging to all policy engines.
+-------------------------------------+ +--------------+
| Load Balancer (eg. HAProxy) | <----+ Push client |
+----+-------------+-------------+----+ +--------------+
| | |
PE | PE | PE | all+DSDs node
+---------+ +---------+ +---------+ +-----------------+
| +-----+ | | +-----+ | | +-----+ | | +-----+ +-----+ |
| | API | | | | API | | | | API | | | | DSD | | DSD | |
| +-----+ | | +-----+ | | +-----+ | | +-----+ +-----+ |
| +-----+ | | +-----+ | | +-----+ | | +-----+ +-----+ |
| | PE | | | | PE | | | | PE | | | | DSD | | DSD | |
| +-----+ | | +-----+ | | +-----+ | | +-----+ +-----+ |
+---------+ +---------+ +---------+ +--------+--------+
| | | |
| | | |
+--+----------+-------------+--------+--------+
| |
| |
+-------+----+ +------------------------+-----------------+
| Oslo Msg | | DBs (policy, config, push data, exec log)|
+------------+ +------------------------------------------+
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