Availability group API reference - Platform - BlueCat Gateway - 24.1

Gateway Administration Guide

Locale
English
Product name
BlueCat Gateway
Version
24.1

For more details on Availability groups and how they work, see High availability and Gateway Availability groups.

The Availability group API consists of a module (availability_group.api) with constants, functions, and structures that you can use in custom workflows that need to interact with Availability groups. A workflow will need to work with Availability groups if its continued operation would be affected during an Availability group failover event — that is, when the Primary Gateway node fails and the Secondary node takes over Gateway requests.

In general, to respond smoothly to failover events within an Availability group, a custom workflow should:

  • Monitor the current role of the node that it runs on.
  • Provide custom code to be called by the Availability group when a failover (or other) event occurs. This code should perform additional operations required to handle the failover event.

The Availability group API provides the following:

  • Constants for values used by Availability groups

  • Functions you can use in custom workflows to get information about the state of the Availability group and the current node’s role in it.

  • Structures (classes) used by the module.

Note: This python-based API is a separate API from the web-based Availability HTTP API endpoints. The Availability API endpoints is a HTTP/HTTPS-based interface that lets external systems acquire information about a Gateway Availability group through the use of URI endpoints.

 

Performing different operations based on the node state

Sometimes a workflow needs to do different things based on whether the node that's running it is a Primary (active) node or a Secondary (passive or standby) node. You can gather information about the local node with the get_node_state() function, performing the necessary operations depending on the results.

Tip: The get_node_state() function doesn't just retrieve information about the role of the local node. It also tells you whether the node is currently connected to the DNS server and details about the last heartbeat from the Primary node.

 

Subscribing to Availability group failover events

The Availability group's subscribe() function lets you register a callback handler for Availability group-related events. When that event occurs (like a failover between the Primary and Secondary nodes), the callback function that you specify is called. That function can then perform any special processing or operations needed to let the workflow continue operations smoothly. It means your workflow doesn't need to continuously monitor the Availability group for its status.

For example, to specify a function to run when a Gateway node changes its role between Primary and Secondary, you would subscribe to the NODE_ROLE_CHANGED event.

Tip: For sample code that subscribes to this event, see the API reference page for subscribe().