[openstack-dev] [oslo][kolla][openstack-helm][tripleo][all] Storing configuration options in etcd(?)

Davanum Srinivas davanum at gmail.com
Tue Mar 21 21:26:14 UTC 2017


the /v3alpha HTTP API  (grpc-gateway) supports watch

-- Dims

On Tue, Mar 21, 2017 at 5:22 PM, Jay Pipes <jaypipes at gmail.com> wrote:
> On 03/21/2017 04:29 PM, Clint Byrum wrote:
>> Excerpts from Doug Hellmann's message of 2017-03-15 15:35:13 -0400:
>>> Excerpts from Thomas Herve's message of 2017-03-15 09:41:16 +0100:
>>>> On Wed, Mar 15, 2017 at 12:05 AM, Joshua Harlow <harlowja at fastmail.com>
>>>> wrote:
>>>>> * How does reloading work (does it)?
>>>> No. There is nothing that we can do in oslo that will make services
>>>> magically reload configuration. It's also unclear to me if that's
>>>> something to do. In a containerized environment, wouldn't it be
>>>> simpler to deploy new services? Otherwise, supporting signal based
>>>> reload as we do today should be trivial.
>>> Reloading works today with files, that's why the question is important
>>> to think through. There is a special flag to set on options that are
>>> "mutable" and then there are functions within oslo.config to reload.
>>> Those are usually triggered when a service gets a SIGHUP or something
>>> similar.
>>> We need to decide what happens to a service's config when that API
>>> is used and the backend is etcd. Maybe nothing, because every time
>>> any config option is accessed the read goes all the way through to
>>> etcd? Maybe a warning is logged because we don't support reloads?
>>> Maybe an error is logged? Or maybe we flush the local cache and start
>>> reading from etcd on future accesses?
>> etcd provides the ability to "watch" keys. So one would start a thread
>> that just watches the keys you want to reload on, and when they change
>> that thread will see a response and can reload appropriately.
>> https://coreos.com/etcd/docs/latest/dev-guide/api_reference_v3.html
> Yep. Unfortunately, you won't be able to start an eventlet greenthread to
> watch an etcd3/gRPC key. The python grpc library is incompatible with
> eventlet/gevent's monkeypatching technique and causes a complete program
> hang if you try to communicate with the etcd3 server from a greenlet. Fun!
> So, either use etcd2 (the no-longer-being-worked-on HTTP API) or don't use
> eventlet in your client service.
> Best,
> -jay
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Davanum Srinivas :: https://twitter.com/dims

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