11cb42f396
When starting nova-compute for the first time with a new node, the ResourceTracker will create a new ComputeNode record in _init_compute_node but without all of the fields set on the ComputeNode, for example "free_disk_gb". Later _update_usage_from_instances will set some fields on the ComputeNode record (even if there are no instances on the node, why - I don't know) like free_disk_gb. This will make the eventual call from _update() to _resource_change() update the value in the old_resouces dict and return True, and then _update() will try to update those ComputeNode changes to the database. If that update fails, for example due to a DBConnectionError, the value in old_resources will still be for the current version of the node in memory but not what is actually in the database. Note that this failure does not result in the compute service failing to start because ComputeManager._update_available_resource_for_node traps the Exception and just logs it. A subsequent trip through the RT._update() method - because of the update_available_resource periodic task - will call _resource_change but because old_resource matches the current state of the node, it returns False and the RT does not attempt to persist the changes to the DB. _update() will then go on to call _update_to_placement which will create the resource provider in placement along with its inventory, making it potentially a candidate for scheduling. This can be a problem later in the scheduler because the HostState._update_from_compute_node method may skip setting fields on the HostState object if free_disk_gb is not set in the ComputeNode record - which can then break filters and weighers later in the scheduling process (see bug 1834691 and bug 1834694). The fix proposed here is simple: if the ComputeNode.save() in RT._update() fails, restore the previous value in old_resources so that the subsequent run through _resource_change will compare the correct state of the object and retry the update. An alternative to this would be killing the compute service on startup if there is a DB error but that could have unintended side effects, especially if the DB error is transient and can be fixed on the next try. Obviously the scheduler code needs to be more robust also, but those improvements are left for separate changes related to the other bugs mentioned above. Also, ComputeNode.update_from_virt_driver could be updated to set free_disk_gb if possible to workaround the tight coupling in the HostState._update_from_compute_node code, but that's also sort of a whack-a-mole type change best made separately. Change-Id: Id3c847be32d8a1037722d08bf52e4b88dc5adc97 Closes-Bug: #1834712
Team and repository tags
OpenStack Nova
OpenStack Nova provides a cloud computing fabric controller, supporting a wide variety of compute technologies, including: libvirt (KVM, Xen, LXC and more), Hyper-V, VMware, XenServer, OpenStack Ironic and PowerVM.
Use the following resources to learn more.
API
To learn how to use Nova's API, consult the documentation available online at:
For more information on OpenStack APIs, SDKs and CLIs in general, refer to:
Operators
To learn how to deploy and configure OpenStack Nova, consult the documentation available online at:
In the unfortunate event that bugs are discovered, they should be reported to the appropriate bug tracker. If you obtained the software from a 3rd party operating system vendor, it is often wise to use their own bug tracker for reporting problems. In all other cases use the master OpenStack bug tracker, available at:
Developers
For information on how to contribute to Nova, please see the contents of the CONTRIBUTING.rst.
Any new code must follow the development guidelines detailed in the HACKING.rst file, and pass all unit tests.
Further developer focused documentation is available at:
Other Information
During each Summit and Project Team Gathering, we agree on what the whole community wants to focus on for the upcoming release. The plans for nova can be found at: