Open Stack

On 12/08/13 16:52 -0400, Doug Hellmann wrote:
>On Mon, Aug 12, 2013 at 4:11 PM, Clint Byrum <clint at fewbar.com> wrote:
>
>> Excerpts from Doug Hellmann's message of 2013-08-12 12:08:58 -0700:
>> > On Fri, Aug 9, 2013 at 11:56 AM, Clint Byrum <clint at fewbar.com> wrote:
>> >
>> > > Excerpts from Sandy Walsh's message of 2013-08-09 06:16:55 -0700:
>> > > >
>> > > > On 08/08/2013 11:36 PM, Angus Salkeld wrote:
>> > > > > On 08/08/13 13:16 -0700, Clint Byrum wrote:
>> > > > >> Last night while reviewing a feature which would add more events
>> to
>> > > the
>> > > > >> event table, it dawned on me that the event table really must be
>> > > removed.
>> > > > >
>> > > > >
>> > > > >>
>> > > > >> https://bugs.launchpad.net/heat/+bug/1209492
>> > > > >>
>> > > > >> tl;dr: users can write an infinite number of rows to the event
>> table
>> > > at
>> > > > >> a fairly alarming rate just by creating and updating a very large
>> > > stack
>> > > > >> that has no resources that cost any time or are even billable
>> (like an
>> > > > >> autoscaling launch configuration).
>> > > > >>
>> > > > >> The table has no purge function, so the only way to clear out old
>> > > events
>> > > > >> is to delete the stack, or manually remove them directly in the
>> > > database.
>> > > > >>
>> > > > >> We've all been through this before, logging to a database seems
>> great
>> > > > >> until you actually do it.
>> > > > >>
>> > > > >> I have some ideas for how to solve it, but I wanted to get a wider
>> > > > >> audience:
>> > > > >>
>> > > > >> 1) Make the event list a ring buffer. Have rows 0 -
>> $MAX_BUFFER_SIZE
>> > > in
>> > > > >> each stack, and simply write each new event to the next open
>> position,
>> > > > >> wrapping at $MAX_BUFFER_SIZE. Pros: little change to current code,
>> > > > >> just need an offset column added and code that will properly wrap
>> to 0
>> > > > >> at $MAX_BUFFER_SIZE. Cons: still can incur heavy transactional
>> load on
>> > > > >> the database server.A
>> > > > >>
>> > > > >> 1.b) Same, but instead of rows, just maintain a blob and append
>> the
>> > > rows
>> > > > >> as json list. Lowers transactional load but would push some load
>> onto
>> > > > >> the API servers and such to parse these out, and would make
>> pagination
>> > > > >> challenging. Blobs also can be a drain on DB server performance.
>> > > > >>
>> > > > >> 2) Write a purge script. Delete old ones. Pros: No code change,
>> just
>> > > > >> new code to do purging. Cons: same as 1, plus more vulnerability
>> to an
>> > > > >> aggressive attacker who can fit a lot of data in between purges.
>> Also
>> > > > >> large scale deletes can be really painful (see: keystone sql token
>> > > > >> backend).
>> > > > >>
>> > > > >> 3) Log events to Swift. I can't seem to find information on how/if
>> > > > >> appending works there. Tons of tiny single-row files is an option,
>> > > but I
>> > > > >> want to hear from people with more swift knowledge if that is a
>> > > viable,
>> > > > >> performant option. Pros: Scale to the moon. Can charge tenant for
>> > > usage
>> > > > >> and let them purge events as needed. Cons: Adds swift as a
>> requirement
>> > > > >> of Heat.
>> > > > >>
>> > > > >> 4) Provide a way for users to receive logs via HTTP POST. Pros:
>> Simple
>> > > > >> and punts the problem to the users. Cons: users will be SoL if
>> they
>> > > > >> don't have a place to have logs posted to.
>> > > > >>
>> > > > >> 5) Provide a way for users to receive logs via messaging service
>> like
>> > > > >> Marconi.  Pros/Cons: same as HTTP, but perhaps a little more
>> confusing
>> > > > >> and ambitious given Marconi's short existence.
>> > > > >>
>> > > > >> 6) Provide a pluggable backend for logging. This seems like the
>> way
>> > > most
>> > > > >> OpenStack projects solve these issues, which is to let the
>> deployers
>> > > > >> choose and/or provide their own way to handle a sticky problem.
>> Pros:
>> > > > >> Simple and flexible for the future. Cons: Would require writing at
>> > > least
>> > > > >> one backend provider that does what the previous 5 options
>> suggest.
>> > > > >>
>> > > > >> To be clear: Heat cannot really exist without this, as it is the
>> only
>> > > way
>> > > > >> to find out what your stack is doing or has done.
>> > > > >
>> > > > > btw Clint I have ditched that "Recorder" patch as Ceilometer is
>> > > > > getting a Alarm History api soon, so we can defer to that for that
>> > > > > functionality (alarm transitions).
>> > > > >
>> > > > > But we still need a better way to record events/logs for the user.
>> > > > > So I make this blueprint a while ago:
>> > > > > https://blueprints.launchpad.net/heat/+spec/user-visible-logs
>> > > > >
>> > > > > I am becomming more in favor of user options rather than deployer
>> > > > > options if possible. So provide resources for Marconi, Meniscus and
>> > > > > what ever...
>> > > > > Although what is nice about Marconi is you could then hook up what
>> > > > > ever you want to it.
>> > > >
>> > > > Logs are one thing (and Meniscus is a great choice for that), but
>> events
>> > > > are the very thing CM is designed to handle. Wouldn't it make sense
>> to
>> > > > push them back into there?
>> > > >
>> > >
>> > > I'm not sure these events make sense in the current Ceilometer (I
>> assume
>> > > that is "CM" above) context. These events are:
>> > >
>> > > ... Creating stack A
>> > > ... Creating stack A resource A
>> > > ... Created stack A resource A
>> > > ... Created stack A
>> > >
>> > > Users will want to be able to see all of the events for a stack, and
>> > > likely we need to be able to paginate through them as well.
>> > >
>> > > They are fundamental and low level enough for Heat that I'm not sure
>> > > putting them in Ceilometer makes much sense, but maybe I don't
>> understand
>> > > Ceilometer..  or "CM" is something else entirely. :)
>> > >
>> >
>> > CM is indeed ceilometer.
>> >
>> > The plan for the event API there is to make it admin-only (at least for
>> > now). If this is data the user wants to see, that may change the plan for
>> > the API or may mean storing it in ceilometer isn't a good fit.
>> >
>>
>> Visibility into these events is critical to tracking the progress of
>> any action done to a Heat stack:
>>
>>
>> +---------------------+----+------------------------+--------------------+----------------------+
>> | logical_resource_id | id | resource_status_reason | resource_status    |
>> event_time           |
>>
>> +---------------------+----+------------------------+--------------------+----------------------+
>> | AccessPolicy        | 24 | state changed          | CREATE_IN_PROGRESS |
>> 2013-08-12T19:45:36Z |
>> | AccessPolicy        | 25 | state changed          | CREATE_COMPLETE    |
>> 2013-08-12T19:45:36Z |
>> | User                | 26 | state changed          | CREATE_IN_PROGRESS |
>> 2013-08-12T19:45:36Z |
>> | Key                 | 28 | state changed          | CREATE_IN_PROGRESS |
>> 2013-08-12T19:45:38Z |
>> | User                | 27 | state changed          | CREATE_COMPLETE    |
>> 2013-08-12T19:45:38Z |
>> | Key                 | 29 | state changed          | CREATE_COMPLETE    |
>> 2013-08-12T19:45:39Z |
>> | notcompute          | 30 | state changed          | CREATE_IN_PROGRESS |
>> 2013-08-12T19:45:40Z |
>>
>> +---------------------+----+------------------------+--------------------+----------------------+
>>
>> So unless there is a plan to make this a user centric service, it does
>> not seem like a good fit.
>>
>> > Are these "events" transmitted in the same way as notifications? If so,
>> we
>> > may already have the data.
>> >
>>
>> The Heat engine records them while working on the stack. They have a
>> fairly narrow, well defined interface, so it should be fairly easy to
>> address the storage issue with a backend abstraction.
>>
>
>OK. The term "event" frequently means "notification" for ceilometer, but it
>sounds like it's completely different in this case.

Yeah, not really related. But we need to add RPC Notifications to Heat
soon so people can bill on a stack basis (create/update/delete/exist).

What we are talking about here is logging really but we want to get it
to the end user (that does not have access to the infrastructure's
syslog). 


-Angus

>
>Doug
>
>
>>
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>>

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