doc: add provider driver development instructions

Change-Id: I31642883f2bfb99e30820ddf72be3feedb66943e
Tristan Cacqueray 4 years ago
parent ff186a53d3
commit 1ff1a253b5

@ -66,3 +66,84 @@ Drivers
.. autoclass:: nodepool.driver.ProviderConfig
Writing A New Provider Driver
Nodepool drivers are loaded from the nodepool/drivers directory. A driver
is composed of three main objects:
- A ProviderConfig to manage validation and loading of the provider.
- A Provider to manage resource allocations.
- A NodeRequestHandler to manage nodeset (collection of resource) allocations.
Those objects are referenced from the Driver main interface that needs to
be implemented in the file of the driver directory.
The ProviderConfig is constructed with the driver object and the provider
configuration dictionary.
The main procedures of the ProviderConfig are:
- getSchema() exposes a voluptuous schema of the provider configuration.
- load(config) parses the provider configuration. Note that the config
argument is the global Nodepool.yaml configuration. Each provided labels
need to be referenced back to the global config.labels dictionary so
that the launcher service know which provider provide which labels.
The Provider is constructed with the ProviderConfig.
The main procedures of the Provider are:
- cleanupNode(external_id) terminates a resource
- listNodes() returns the list of existing resources. This procedure needs to
map the nodepool_node_id with each resource. If the provider doesn't support
resource metadata, the driver needs to implement a storage facility to
associate resource created by Nodepool with the internal nodepool_node_id.
The launcher periodically look for non-existent node_id in listNodes() to
delete any leaked resources.
- getRequestHandler(pool, request) returns a NodeRequestHandler object to manage
the creation of resources. The contract between the handler and the provider is
free form. As a rule of thumb, the handler should be in charge of interfacing
with Nodepool's database while the provider should provides primitive to create
resources. For example the Provider is likely to implement a
createResource(pool, label) procedure that will be used by the handler.
The NodeRequestHandler is constructed with the assigned pool and the request object.
Before the handler is used, the following attributes are set:
* self.provider : the provider configuration.
* self.pool : the pool configuration.
* self.zk : the database client.
* self.manager : the Provider object.
The main procedures of the NodeRequestHandler are:
- launch(node) starts the creation of a new resource.
- launchesComplete() returns True if all the node of the nodesets self
attributes are READY.
An Handler may not have to launch each node of the nodesets as Nodepool will
re-use existing nodes.
The launch procedure usually consists of the following operations:
- Use the provider to create the resources associated with the node label.
Once an external_id is obtained, it should be stored to the node.external_id.
- Once the resource is created, READY should be stored to the node.state.
Otherwise raise an exception to restart the launch attempt.