> On Dec 16, 2015, at 6:24 PM, Joshua Harlow <harlo...@fastmail.com> wrote: > > SURO wrote: >> Hi all, >> Please review and provide feedback on the following design proposal for >> implementing the blueprint[1] on async-container-operations - >> >> 1. Magnum-conductor would have a pool of threads for executing the >> container operations, viz. executor_threadpool. The size of the >> executor_threadpool will be configurable. [Phase0] >> 2. Every time, Magnum-conductor(Mcon) receives a >> container-operation-request from Magnum-API(Mapi), it will do the >> initial validation, housekeeping and then pick a thread from the >> executor_threadpool to execute the rest of the operations. Thus Mcon >> will return from the RPC request context much faster without blocking >> the Mapi. If the executor_threadpool is empty, Mcon will execute in a >> manner it does today, i.e. synchronously - this will be the >> rate-limiting mechanism - thus relaying the feedback of exhaustion. >> [Phase0] >> How often we are hitting this scenario, may be indicative to the >> operator to create more workers for Mcon. >> 3. Blocking class of operations - There will be a class of operations, >> which can not be made async, as they are supposed to return >> result/content inline, e.g. 'container-logs'. [Phase0] >> 4. Out-of-order considerations for NonBlocking class of operations - >> there is a possible race around condition for create followed by >> start/delete of a container, as things would happen in parallel. To >> solve this, we will maintain a map of a container and executing thread, >> for current execution. If we find a request for an operation for a >> container-in-execution, we will block till the thread completes the >> execution. [Phase0] > > Does whatever do these operations (mcon?) run in more than one process?
Yes, there may be multiple copies of magnum-conductor running on separate hosts. > Can it be requested to create in one process then delete in another? If so is > that map some distributed/cross-machine/cross-process map that will be > inspected to see what else is manipulating a given container (so that the > thread can block until that is not the case... basically the map is acting > like a operation-lock?) That’s how I interpreted it as well. This is a race prevention technique so that we don’t attempt to act on a resource until it is ready. Another way to deal with this is check the state of the resource, and return a “not ready” error if it’s not ready yet. If this happens in a part of the system that is unattended by a user, we can re-queue the call to retry after a minimum delay so that it proceeds only when the ready state is reached in the resource, or terminated after a maximum number of attempts, or if the resource enters an error state. This would allow other work to proceed while the retry waits in the queue. > If it's just local in one process, then I have a library for u that can solve > the problem of correctly ordering parallel operations ;) What we are aiming for is a bit more distributed. Adrian >> This mechanism can be further refined to achieve more asynchronous >> behavior. [Phase2] >> The approach above puts a prerequisite that operations for a given >> container on a given Bay would go to the same Magnum-conductor instance. >> [Phase0] >> 5. The hand-off between Mcon and a thread from executor_threadpool can >> be reflected through new states on the 'container' object. These states >> can be helpful to recover/audit, in case of Mcon restart. [Phase1] >> >> Other considerations - >> 1. Using eventlet.greenthread instead of real threads => This approach >> would require further refactoring the execution code and embed yield >> logic, otherwise a single greenthread would block others to progress. >> Given, we will extend the mechanism for multiple COEs, and to keep the >> approach straight forward to begin with, we will use 'threading.Thread' >> instead of 'eventlet.greenthread'. >> >> >> Refs:- >> [1] - >> https://blueprints.launchpad.net/magnum/+spec/async-container-operations >> > > __________________________________________________________________________ > OpenStack Development Mailing List (not for usage questions) > Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev __________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev