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Difference between revisions of "Nova-Cells-v2"

(→‎Nova Cells v2)
(→‎Open Questions)
 
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=== Bugs ===
 
=== Bugs ===
  
−
* https://bugs.launchpad.net/nova/+bug/1656276 - Error running nova-manage cell_v2 simple_cell_setup when configuring nova with puppet-nova
+
* https://bugs.launchpad.net/openstack-manuals/+bug/1673616 - Scaling in Operations Guide - cells section needs to be updated
−
* https://bugs.launchpad.net/nova/+bug/1649341 - Undercloud upgrade fails with "Cell mappings are not created, but required for Ocata"
+
* https://bugs.launchpad.net/nova/+bug/1682060 - empty nova service and hypervisor list
−
** Fixed on master in Nova, backport proposed to stable/newton. However, this change caused issues for TripleO on master which is bug 1656276 above.
+
** Fixed with a docs patch: https://review.openstack.org/#/c/456923/ (mriedem)
−
* https://bugs.launchpad.net/nova/+bug/1656017 - nova-manage cell_v2 map_cell0 always returns a non-0 exit code
+
* https://bugs.launchpad.net/nova/+bug/1682693 - tags and not-tags cannot work properly
 +
** Patch from Kevin Zheng: https://review.openstack.org/#/c/456872/ - needs to be backported to ocata and newton
 +
* https://bugs.launchpad.net/trove/+bug/1682845 - nova's server group API returns deleted instances as members
 +
** Original regression is reverted: https://review.openstack.org/#/c/457097/
 +
** TODO(dansmith) to provide a proper fix
 +
 
 +
=== Blueprints ===
 +
 
 +
These are all currently targeted for the Pike release.
 +
 
 +
* https://blueprints.launchpad.net/nova/+spec/discover-hosts-faster
 +
* https://blueprints.launchpad.net/nova/+spec/cells-aware-api
 +
* https://blueprints.launchpad.net/nova/+spec/cells-count-resources-to-check-quota-in-api
 +
* https://blueprints.launchpad.net/nova/+spec/list-instances-using-searchlight
 +
* https://blueprints.launchpad.net/nova/+spec/service-hyper-uuid-in-api
 +
* https://blueprints.launchpad.net/nova/+spec/convert-consoles-to-objects
  
 
=== TODOs ===
 
=== TODOs ===
  
−
* The deployment/upgrade process needs to be documented in more than just the release notes.
 
−
** dansmith was going to work on a blog post to start this.
 
−
** On a side note, we should also have man pages for the cell_v2 commands because there is confusion around the inputs and outputs and how return codes should be treated, i.e. is 1 an error or not?
 
−
** alaski's older docs patch (which is probably out of date now but might be useful) is here: https://review.openstack.org/#/c/267153/
 
−
* Integrate the 'nova-status upgrade check' CLI into the CI/QA system (grenade).
 
 
* Older tracking etherpads (these may be out of date):
 
* Older tracking etherpads (these may be out of date):
 
** https://etherpad.openstack.org/p/cellsV2-remaining-work-items
 
** https://etherpad.openstack.org/p/cellsV2-remaining-work-items
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=== Open Questions ===
 
=== Open Questions ===
 +
 +
* How will we handle multiple cells where each cell has its own independent ceph cluster? (brought up in #openstack-nova by mnaser)
 +
** If glance has its own ceph cluster where it stores images and each cell has its own ceph cluster, then each instance create will require a download of the image from glance since the glance ceph cluster can't be reached by any cell. How can we handle the inefficiency?
 +
*** Idea from mnaser: could we cache images in the imagebackend (instead of on the hypervisor disk) so that each cell gets a copy of the image and can re-use it instead of re-downloading from glance every time?
 +
*** Workaround from mnaser: store images multiple times in glance (glance supports multiple image locations), once per cell ceph cluster, and nova could try locations until it finds an image whose ceph cluster it can access.
 +
**** (melwitt): I'm not sure how that works in glance, how it could access multiple ceph clusters and track separate credentials per ceph cluster?
 +
**** (mnaser): Glance exposes 'locations' attribute in the API which is a list of locations.  In the [https://github.com/openstack/nova/blob/master/nova/virt/libvirt/imagebackend.py#L922-L925 clone] function for the RBD image driver, Nova attempts to check if it can clone from this location using `is_clonable()`.  You can see from the [https://github.com/openstack/nova/blob/master/nova/virt/libvirt/storage/rbd_utils.py#L199-L225 is_cloneable] codebase that one of the checks is if the fsid of the Ceph cluster is the same as the one Nova connects to.  FSID's are supposed to be globally unique so it would return false.  I am assuming it'll keep looping until it hits the one that matches the fsid of the ceph cluster inside the cell!
  
 
* Should the computes self-register with a cell when the compute_nodes record is created from the ResourceTracker? https://review.openstack.org/#/c/369634/
 
* Should the computes self-register with a cell when the compute_nodes record is created from the ResourceTracker? https://review.openstack.org/#/c/369634/
−
* Why can't we create an empty cell, i.e. a cell mapping with no computes? This is a fresh-install scenario.
+
** How would the computes know which cell to map to? We could add something to the model to flag a 'default' or 'staging' cell mapping, or put something into nova.conf on the compute node.
 +
** If we auto-register into a default/staging cell, how do we move hosts to other cells? nova-manage CLI?
 +
** We have an option to auto-map hosts from the scheduler since Ocata, with improvements being made in Pike: https://blueprints.launchpad.net/nova/+spec/discover-hosts-faster
  
 
=== Manifesto ===
 
=== Manifesto ===
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=== Code Review ===
 
=== Code Review ===
−
* https://review.openstack.org/#/q/topic:bp/cells-scheduling-interaction
+
* See the cells v2 section in the Pike review priorities etherpad: https://etherpad.openstack.org/p/pike-nova-priorities-tracking
−
* Otherwise see the cells v2 section in the Ocata review priorities etherpad: https://etherpad.openstack.org/p/ocata-nova-priorities-tracking
 
  
 
=== References ===
 
=== References ===

Latest revision as of 22:41, 12 December 2017

Nova Cells v2

Bugs

Blueprints

These are all currently targeted for the Pike release.

TODOs

Open Questions

  • How will we handle multiple cells where each cell has its own independent ceph cluster? (brought up in #openstack-nova by mnaser)
    • If glance has its own ceph cluster where it stores images and each cell has its own ceph cluster, then each instance create will require a download of the image from glance since the glance ceph cluster can't be reached by any cell. How can we handle the inefficiency?
      • Idea from mnaser: could we cache images in the imagebackend (instead of on the hypervisor disk) so that each cell gets a copy of the image and can re-use it instead of re-downloading from glance every time?
      • Workaround from mnaser: store images multiple times in glance (glance supports multiple image locations), once per cell ceph cluster, and nova could try locations until it finds an image whose ceph cluster it can access.
        • (melwitt): I'm not sure how that works in glance, how it could access multiple ceph clusters and track separate credentials per ceph cluster?
        • (mnaser): Glance exposes 'locations' attribute in the API which is a list of locations. In the clone function for the RBD image driver, Nova attempts to check if it can clone from this location using `is_clonable()`. You can see from the is_cloneable codebase that one of the checks is if the fsid of the Ceph cluster is the same as the one Nova connects to. FSID's are supposed to be globally unique so it would return false. I am assuming it'll keep looping until it hits the one that matches the fsid of the ceph cluster inside the cell!
  • Should the computes self-register with a cell when the compute_nodes record is created from the ResourceTracker? https://review.openstack.org/#/c/369634/
    • How would the computes know which cell to map to? We could add something to the model to flag a 'default' or 'staging' cell mapping, or put something into nova.conf on the compute node.
    • If we auto-register into a default/staging cell, how do we move hosts to other cells? nova-manage CLI?
    • We have an option to auto-map hosts from the scheduler since Ocata, with improvements being made in Pike: https://blueprints.launchpad.net/nova/+spec/discover-hosts-faster

Manifesto

http://docs.openstack.org/developer/nova/cells.html#manifesto

Testing

https://etherpad.openstack.org/p/nova-cells-testing

DB Table Analysis

https://etherpad.openstack.org/p/nova-cells-table-analysis

Scheduling requirements

https://etherpad.openstack.org/p/nova-cells-scheduling-requirements

Code Review

References

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