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From Zameer Manji <zma...@apache.org>
Subject Re: 答复: Discussion on review request 51536
Date Sat, 03 Sep 2016 01:28:57 GMT
Resending my emails from a domain that has mailing list friendly DMARC
settings.

It seems that we have achieved some consensus on the design, others feel
free to weigh in.

On Fri, Sep 2, 2016 at 5:29 PM, Zameer Manji <zmanji@uber.com> wrote:

> Kai,
>
> We have had coupled deploys before, I don't think it's too terrible. It's
> something to note in the release notes and some operational pain for large
> users.
>
> On Fri, Sep 2, 2016 at 4:42 PM, 黄 凯 <texasred2013@hotmail.com> wrote:
>
> > Another concern is that once we rolled out the new executor, we should
> > rolled out a new client in order to use the health-check feature. Hence
> the
> > executor and client rolling out process seem to be coupled.
> >
> >
> >
> >
> > ------------------------------
> > *发件人:* 黄 凯 <texasred2013@hotmail.com>
> > *发送时间:* 2016年9月3日 7:23
> > *收件人:* Zameer Manji; dev@aurora.apache.org
> > *抄送:* Joshua Cohen; serb@apache.org; caldima@gmail.com;
> > rdelval1@binghamton.edu
> > *主题:* 答复: Discussion on review request 51536
> >
> >
> > Thanks for the new proposal, Zameer. It sounds good to me. The benefit is
> > that it does not alter the current infrastructure too much.
> >
> >
> > However, there is one thing to keep in mind:
> >
> > we currently do a check to ensure watch_sec is longer than
> > initial_interval_secs. We will have to remove the alert message if we
> > choose to skip watch_sec by setting it as zero.
> >
> >
> > So the new configuration will not support executor-driven health check
> > unless the executors are rolled out 100%.
> >
> >
> > Does this tradeoff seems OK for us, Maxim?
> >
> >
> > Kai
> >
> >
> > ------------------------------
> > *发件人:* Zameer Manji <zmanji@uber.com>
> > *发送时间:* 2016年9月3日 6:53
> > *收件人:* dev@aurora.apache.org
> > *抄送:* 黄 凯; Joshua Cohen; serb@apache.org; caldima@gmail.com;
> > rdelval1@binghamton.edu
> > *主题:* Re: Discussion on review request 51536
> >
> >
> >
> > On Fri, Sep 2, 2016 at 3:24 PM, Maxim Khutornenko <maxim@apache.org>
> > wrote:
> >
> >> Need to correct a few previous statements:
> >>
> >> > Also we do not want to expose this message to users.
> >> This is incorrect. The original design proposal suggested to show this
> >> message in the UI as: "Task is healthy"
> >>
> >
> > Does this mean the message in the status update is going to be exactly,
> > "Task is healthy" and the scheduler is going to check for this string in
> > the `TASK_RUNNING` status update? This means we are going to establish a
> > communication
> > mechanism between the executor and scheduler that's not defined by a
> > schema. I feel that's worse than putting JSON in there and having the
> > scheduler parse it.
> >
> >
> >> > The Mesos API isn't designed for packing arbitrary data
> >> > in the status update message.
> >> Don't think I agree, this is exactly what this field is for [1] and we
> >> already use it for other states [2].
> >>
> >
> > I guess I should have said 'structured arbitrary data'. The
> informational,
> > messages are fine and we plumb them blindly into our logging and UI. I'm
> > not convinced we should start putting JSON or something more structured
> in
> > there. That's yet another schema we have and yet another versioning story
> > we have to go though. This also complicates matters for custom executor
> > authors.
> >
> >
> >>
> >> > I would be open to just saying that scheduler version
> >> > 0.16 (or 0.17) just assumes the executor transitions to
> >> > RUNNING once a task is healthy and dropping
> >> > `watch_secs`entirely.
> >> We can't drop 'watch_secs' entirely as we still have to babysit job
> >> updates that don't have health checks enabled.
> >>
> >
> > Understood. I guess we can keep it but I'm now frustrated that we have a
> > parameter that is ignored if we set some json in ExecutorConfig.data.
> > Ideally, we don't accept `watch_secs` if we want health check driven
> > updates. As mentioned before I don't like this implicit tightening of the
> > executor and the scheduler.
> >
> >
> >>
> >> As for my take on the above, I favor #1 as the simplest answer to an
> >> already simple question: "Should we use watch_secs for this instance
> >> or not?". That's pretty much it. Scheduler does not need any schema
> >> changes, know what health checks are or if a job has them enabled. At
> >> least not until we attempt to move to centralized health checks
> >> (AURORA-279) but that will be an entirely different design discussion.
> >>
> >> [1] - https://github.com/apache/mesos/blob/master/include/mesos/
> >> mesos.proto#L1605.
> >> [2] - https://github.com/apache/aurora/blob/5cad046fc0f0c4bb79a456
> >> 3cfcff0442b7bf8383/src/main/python/apache/aurora/executor/
> >> aurora_executor.py#L97
> >
> >
> >
> > With all of this in mind, I have another proposal. Why can't we have the
> > executor changes (wait until the task is healthy for RUNNING) *and* read
> > `watch_secs` if it is set? Why not have both of these features and if
> users
> > want purely health checking driven updates they can set this value to 0
> and
> > enable health checks. If they want to have both health checking and time
> > driven updates they can set this to value to the time that they care
> about.
> > If they just want time driven updates they can disable health checking
> and
> > set this value.
> >
> > Then there is no coupling between the executor and the scheduler except
> > for status updates and there is no dependency on the `message` field of
> the
> > status update.
> >
> > We could even treat `watch_secs` as minimum time in STARTING + RUNNING
> > instead of RUNNING with this change and it becomes the lower bound in the
> > update transition speed. This can ensure that users don't deploy "too
> fast"
> > and end up overwhelming other services if they are deployed too quickly.
> >
> >
> >
> >>
> >>
> >> On Fri, Sep 2, 2016 at 2:26 PM, Zameer Manji <zmanji@apache.org> wrote:
> >> > *cc: Renan*
> >> >
> >> > I think there is some disagreement/discussion on the review because we
> >> have
> >> > not achieved consensus on the design. Since the design doc was
> written,
> >> > Aurora adopted multiple executor support as well non HTTP based
> >> > healthchecking. This invalidates some parts of the original design. I
> >> think
> >> > all of the solutions here are possible amendments to the design doc.
> >> >
> >> > I am not in favor of Solution 2 at all because status updates between
> >> > executor <-> agent <-> master <-> scheduler are designed
to update the
> >> > framework of updates to the task and not really designed to send
> >> arbitrary
> >> > information. Just because the Mesos API provides us with a string
> field
> >> > doesn't mean we should try to pack in arbitrary data. Also, it isn't
> >> clear
> >> > what other capabilities we might add in the future so I'm unconvinced
> >> that
> >> > capabilities needs to exist at all. My fear is that we will create the
> >> > infrastructure for capabilities just to serve this need and nothing
> >> else.
> >> >
> >> > I object to Solution 1 along the same lines. The Mesos API isn't
> >> designed
> >> > for packing arbitrary data in the status update message and I don't
> >> think
> >> > we should abuse that and rely on that. Also our current infrastructure
> >> just
> >> > plumbs the message to the UI and I think displaying capabilities is
> not
> >> > something we should do.
> >> >
> >> > I am in favor of Solution 3 which is as close as possible to the
> >> original
> >> > design in the design doc. The design doc says the following:
> >> >
> >> > Scheduler updater will skip the minWaitInInstanceMs (aka watch_secs
> >> >> <https://github.com/apache/aurora/blob/4b43305b33cd8bebdd802
> >> 25a3987b7cc7a8389a2/docs/configuration-reference.md#
> updateconfig-objects
> >> >)
> >> >> grace period any time it detects a named port ‘health’ in task
> >> >> configuration. A RUNNING instance status will signify the end of
> >> instance
> >> >> update.
> >> >
> >> >
> >> > Instead of detecting the 'health' port in the task configuration, we
> >> make
> >> > enabling this feature explicitly by enabling a bit in the task
> >> > configuration with the `executorDrivenUpdates` bit.
> >> >
> >> > I understand this option makes this feature more complex because it
> >> > requires a schema change and requires operators to deploy the executor
> >> to
> >> > all agents before upgrading the client. However, I think that's a one
> >> time
> >> > operational cost as a opposed to long lived design choices that will
> >> affect
> >> > the code.
> >> >
> >> > Further Solution 3 is the most amenable to custom executors and
> >> continues
> >> > our tradition of treating executors as opaque black boxes. I think
> >> there is
> >> > a lot of value in treating executors as black boxes as it leaves the
> >> door
> >> > open to switching our executor to something else and doesn't impose a
> >> > burden to others that want to write their own.
> >> >
> >> > Alternatively, if amending the schema is too much work, I would be
> open
> >> to
> >> > just saying that scheduler version 0.16 (or 0.17) just assumes the
> >> executor
> >> > transitions to RUNNING once a task is healthy and dropping
> `watch_secs`
> >> > entirely. We can put it in the release notes that operators must
> deploy
> >> the
> >> > executor to 100% before deploying the scheduler.
> >> >
> >> >
> >> > On Thu, Sep 1, 2016 at 6:40 PM, 黄 凯 <texasred2013@hotmail.com>
wrote:
> >> >
> >> >> Hi Folks,
> >> >>
> >> >> I'm currently working on a feature on aurora scheduler and executor.
> >> The
> >> >> implementation strategy became controversial on the review board, so
> I
> >> was
> >> >> wondering if I should broadcast it to more audience and initiate a
> >> >> discussion. Please feel free to let me know your thoughts, your help
> is
> >> >> greatly appreciated!
> >> >>
> >> >> The high level goal of this feature is to improve reliability and
> >> >> performance of the Aurora scheduler job updater, by relying on health
> >> check
> >> >> status rather than watch_secs timeout when deciding an individual
> >> instance
> >> >> update state.
> >> >>
> >> >> Please see the original review request *
> https://reviews.apache.org/r/
> >> 51536/
> >> >> <https://reviews.apache.org/r/51536/> *
> >> >> aurora JIRA ticket *https://issues.apache.org/jira/browse/AURORA-894
> >> >> <https://issues.apache.org/jira/browse/AURORA-894>*
> >> >> design doc *https://docs.google.com/docum
> >> ent/d/1ZdgW8S4xMhvKW7iQUX99xZm10NXSxEWR0a-21FP5d94/edit#
> >> >> <https://docs.google.com/document/d/1ZdgW8S4xMhvKW7iQUX99xZm
> >> 10NXSxEWR0a-21FP5d94/edit#>*
> >> >> for more details and background.
> >> >>
> >> >> Note: The design doc becomes a little bit outdated on the "scheduler
> >> >> change summary" part (this is what the review request trying to
> >> address).
> >> >> As a result, I've left some comment to clarify the latest proposed
> >> >> implementation plan for scheduler change.
> >> >>
> >> >> There are two questions I'm trying to address here:
> >> >> *1. How does the scheduler infer the executor version and be backward
> >> >> compatible?*
> >> >> *2. Where do we determine if health check is enabled?*
> >> >>
> >> >> In short, there are 3 different solutions proposed on the review
> board.
> >> >>
> >> >> In the first two approaches, the scheduler will rely on a string to
> >> >> determine the executor version. We determine whether health check is
> >> >> enabled merely on executor side. There will be communication between
> >> the
> >> >> executor and the scheduler.
> >> >> *Solution 1: *
> >> >> *vCurrent executor sends a message in its health check thread during
> >> >> RUNNING state transition, and the vCurrent updater will infer the
> >> executor
> >> >> version from the presence of this message, and skip the watch_secs
if
> >> >> necessary.*
> >> >>
> >> >> *Solution 2:*
> >> >> *Instead of relying on the presence of an arbitrary string in the
> >> message,
> >> >> rely on the presence of a string like:
> >> >> "capabilities:CAPABILITY_1,CAPABILITY-2" where CAPABILITY_1 and
> >> >> CAPABILITY_2 (etc.) are constants defined in api.thrift. Basically
> just
> >> >> formalizing the mechanism and making it a bit more future proof.*
> >> >>
> >> >> In the third solution, the scheduler infers the executor version from
> >> the
> >> >> JobUpdateSettings on scheduler side.
> >> >> *Solution 3:*
> >> >> *Adding a bit to JobUpdateSettings which is ‘executorDrivenUpdates',
> if
> >> >> that is set, the scheduler assumes that the transition from STARTING
> ->
> >> >> RUNNING makes the executor healthy and concurrently, we release
> >> thermos and
> >> >> change HealthCheckConfig to say that it should only go to running
> after
> >> >> healthy*.
> >> >>
> >> >> *Pros and Cons:*
> >> >> The main benefit of Solution 1 is:
> >> >> 1. By using the message in task status update, we don't have to make
> >> any
> >> >> schema change, which makes the design simple.
> >> >> 2. The feature is fully backward-compatible. When we roll out the
> >> vCurrent
> >> >> schedulers and executors, we do not have to instruct the users to
> >> provide
> >> >> additional field in the Job or Update configs, which could confuses
> >> >> customers when the vPrev and vCurrent executor coexist in the
> cluster.
> >> >>
> >> >> Concerns:
> >> >> Relying on the presence of a message makes things brittle. Also we
do
> >> not
> >> >> want to expose this message to users.
> >> >>
> >> >> The benefit of Solution 2 is making the feature more future proof.
> >> >> However, if we do not envision a new executor feature in the short
> >> term,
> >> >> it's not too much different from Solution 1.
> >> >>
> >> >> The benefits of Solution 3 include:
> >> >> 1. We support more than just thermos now (and others rely on custom
> >> >> executors).
> >> >> 2. A lot of things in Aurora treat the executor as opaque. The status
> >> >> update message sent by executor should not be visible to users only
> if
> >> it's
> >> >> an error message.
> >> >>
> >> >> Concerns:
> >> >> 1. In addition to the ‘executorDrivenUpdates' bit that identifies
the
> >> >> executor version, we still need to notify the scheduler if health
> >> check is
> >> >> enabled on vCurrent executor, if not, the scheduler must be able to
> >> fall
> >> >> back to use watch_secs.
> >> >> 2. The users have to provide an additional field in their .aurora
> >> config
> >> >> files. The feature wouldn't be available unless new clients are
> rolled
> >> out
> >> >> as well.
> >> >>
> >> >> Please let me know if I understand your suggestions correctly and
> >> >> hopefully everyone is on the same page!
> >> >>
> >> >> Thanks,
> >> >>
> >> >> Kai
> >> >>
> >>
> >
> >
> >
> > --
> > Zameer Manji
> >
>
>
>
> --
> Zameer Manji
>

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