[Pulp-dev] Lazy for Pulp3
Jeff Ortel
jortel at redhat.com
Thu May 31 22:36:07 UTC 2018
On 05/31/2018 04:39 PM, Brian Bouterse wrote:
> I updated the epic (https://pulp.plan.io/issues/3693) to use this new
> language.
>
> policy=immediate -> downloads now while the task runs (no lazy). Also
> the default if unspecified.
> policy=cache-and-save -> All the steps in the diagram. Content that
> is downloaded is saved so that it's only ever downloaded once.
> policy=cache -> All the steps in the diagram except step 14. If
> squid pushes the bits out of the cache, it will be re-downloaded again
> to serve to other clients requesting the same bits.
These policy names strike me as an odd, non-intuitive mixture. I think
we need to brainstorm on policy names and/or additional attributes to
best capture this. Suggest the epic be updated to describe the "modes"
or use cases without the names for now. I'll try to follow up with
other suggestions.
>
> Also @milan, see inline for answers to your question.
>
> On Wed, May 30, 2018 at 3:48 PM, Milan Kovacik <mkovacik at redhat.com
> <mailto:mkovacik at redhat.com>> wrote:
>
> On Wed, May 30, 2018 at 4:50 PM, Brian Bouterse
> <bbouters at redhat.com <mailto:bbouters at redhat.com>> wrote:
> >
> >
> > On Wed, May 30, 2018 at 8:57 AM, Tom McKay
> <thomasmckay at redhat.com <mailto:thomasmckay at redhat.com>> wrote:
> >>
> >> I think there is a usecase for "proxy only" like is being
> described here.
> >> Several years ago there was a project called thumbslug[1] that
> was used in a
> >> version of katello instead of pulp. It's job was to check
> entitlements and
> >> then proxy content from a cdn. The same functionality could be
> implemented
> >> in pulp. (Perhaps it's even as simple as telling squid not to
> cache anything
> >> so the content would never make it from cache to pulp in
> current pulp-2.)
> >
> >
> > What would you call this policy?
> > policy=proxy?
> > policy=stream-dont-save?
> > policy=stream-no-save?
> >
> > Are the names 'on-demand' and 'immediate' clear enough? Are
> there better
> > names?
> >>
> >>
> >> Overall I'm +1 to the idea of an only-squid version, if others
> think it
> >> would be useful.
> >
> >
> > I understand describing this as a "only-squid" version, but for
> clarity, the
> > streamer would still be required because it is what requests the
> bits with
> > the correctly configured downloader (certs, proxy, etc). The
> streamer
> > streams the bits into squid which provides caching and client
> multiplexing.
>
> I have to admit it's just now I'm reading
> https://docs.pulpproject.org/dev-guide/design/deferred-download.html#apache-reverse-proxy
> <https://docs.pulpproject.org/dev-guide/design/deferred-download.html#apache-reverse-proxy>
> again because of the SSL termination. So the new plan is to use the
> streamer to terminate the SSL instead of the Apache reverse proxy?
>
>
> The plan for right now is to not use a reverse proxy and have the
> client's connection terminate at squid directly either via http or
> https depending on how squid is configured. The Reverse proxy in
> pulp2's design served to validate the signed urls and rewrite them for
> squid. This first implementation won't use signed urls. I believe that
> means we don't need a reverse proxy here yet.
>
>
> W/r the construction of the URL of an artifact, I thought it would be
> stored in the DB, so the Remote would create it during the sync.
>
>
> This is correct. The inbound URL from the client after the redirect
> will still be a reference that the "Pulp content app" will resolve to
> a RemoteArtifact. Then the streamer will use that RemoteArtifact data
> to correctly build the downloader. That's the gist of it at least.
>
>
> >
> > To confirm my understanding this "squid-only" policy would be
> the same as
> > on-demand except that it would *not* perform step 14 from the
> diagram here
> > (https://pulp.plan.io/issues/3693
> <https://pulp.plan.io/issues/3693>). Is that right?
> yup
> >
> >>
> >>
> >> [1] https://github.com/candlepin/thumbslug
> <https://github.com/candlepin/thumbslug>
> >>
> >> On Wed, May 30, 2018 at 8:34 AM, Milan Kovacik
> <mkovacik at redhat.com <mailto:mkovacik at redhat.com>>
> >> wrote:
> >>>
> >>> On Tue, May 29, 2018 at 9:31 PM, Dennis Kliban
> <dkliban at redhat.com <mailto:dkliban at redhat.com>>
> >>> wrote:
> >>> > On Tue, May 29, 2018 at 11:42 AM, Milan Kovacik
> <mkovacik at redhat.com <mailto:mkovacik at redhat.com>>
> >>> > wrote:
> >>> >>
> >>> >> On Tue, May 29, 2018 at 5:13 PM, Dennis Kliban
> <dkliban at redhat.com <mailto:dkliban at redhat.com>>
> >>> >> wrote:
> >>> >> > On Tue, May 29, 2018 at 10:41 AM, Milan Kovacik
> >>> >> > <mkovacik at redhat.com <mailto:mkovacik at redhat.com>>
> >>> >> > wrote:
> >>> >> >>
> >>> >> >> Good point!
> >>> >> >> More the second; it might be a bit crazy to utilize
> Squid for that
> >>> >> >> but
> >>> >> >> first, let's answer the why ;)
> >>> >> >> So why does Pulp need to store the content here?
> >>> >> >> Why don't we point the users to the Squid all the time
> (for the
> >>> >> >> lazy
> >>> >> >> repos)?
> >>> >> >
> >>> >> >
> >>> >> > Pulp's Streamer needs to fetch and store the content
> because that's
> >>> >> > Pulp's
> >>> >> > primary responsibility.
> >>> >>
> >>> >> Maybe not that much the storing but rather the content views
> >>> >> management?
> >>> >> I mean the partitioning into repositories, promoting.
> >>> >>
> >>> >
> >>> > Exactly this. We want Pulp users to be able to reuse content
> that was
> >>> > brought in using the 'on_demand' download policy in other
> repositories.
> >>> I see.
> >>>
> >>> >
> >>> >>
> >>> >> If some of the content lived in Squid and some lived
> >>> >> > in Pulp, it would be difficult for the user to know what
> content is
> >>> >> > actually
> >>> >> > available in Pulp and what content needs to be fetched
> from a remote
> >>> >> > repository.
> >>> >>
> >>> >> I'd say the rule of the thumb would be: lazy -> squid,
> regular -> pulp
> >>> >> so not that difficult.
> >>> >> Maybe Pulp could have a concept of Origin, where folks
> upload stuff to
> >>> >> a Pulp repo, vs. Proxy for it's repo storage policy?
> >>> >>
> >>> >
> >>> > Squid removes things from the cache at some point. You can
> probably
> >>> > configure it to never remove anything from the cache, but
> then we would
> >>> > need
> >>> > to implement orphan cleanup that would work across two
> systems: pulp
> >>> > and
> >>> > squid.
> >>>
> >>> Actually "remote" units wouldn't need orphan cleaning from the
> disk,
> >>> just dropping them from the DB would suffice.
> >>>
> >>> >
> >>> > Answering that question would still be difficult. Not all
> content that
> >>> > is in
> >>> > the repository that was synced using on_demand download
> policy will be
> >>> > in
> >>> > Squid - only the content that has been requested by clients.
> So it's
> >>> > still
> >>> > hard to know which of the content units have been downloaded
> and which
> >>> > have
> >>> > not been.
> >>>
> >>> But the beauty is exactly in that: we don't have to track
> whether the
> >>> content is downloaded if it is reverse-proxied[1][2].
> >>> Moreover, this would work both with and without a proxy
> between Pulp
> >>> and the Origin of the remote unit.
> >>> A "remote" content artifact might just need to carry it's URL
> in a DB
> >>> column for this to work; so the async artifact model, instead
> of the
> >>> "policy=on-demand" would have a mandatory remote "URL"
> attribute; I
> >>> wouldn't say it's more complex than tracking the "policy"
> attribute.
> >>>
> >>> >
> >>> >
> >>> >>
> >>> >> >
> >>> >> > As Pulp downloads an Artifact, it calculates all the
> checksums and
> >>> >> > it's
> >>> >> > size. It then performs validation based on information
> that was
> >>> >> > provided
> >>> >> > from the RemoteArtifact. After validation is performed, the
> >>> >> > Artifact, is
> >>> >> > saved to the database and it's final place in
> >>> >> > /var/lib/content/artifacts/.
> >>> >>
> >>> >> This could be still achieved by storing the content just
> temporarily
> >>> >> in the Squid proxy i.e use Squid as the content source, not
> the disk.
> >>> >>
> >>> >> > Once this information is in the database, Pulp's web
> server can
> >>> >> > serve
> >>> >> > the
> >>> >> > content without having to involve the Streamer or Squid.
> >>> >>
> >>> >> Pulp might serve just the API and the metadata, the content
> might be
> >>> >> redirected to the Proxy all the time, correct?
> >>> >> Doesn't Crane do that btw?
> >>> >
> >>> >
> >>> > Theoretically we could do this, but in practice we would run
> into
> >>> > problems
> >>> > when we needed to scale out the Content app. Right now when
> the Content
> >>> > app
> >>> > needs to be scaled, a user can launch another machine that
> will run the
> >>> > Content app. Squid does not support that kind of scaling.
> Squid can
> >>> > only
> >>> > take advantage of additional cores in a single machine
> >>>
> >>> I don't think I understand; proxies are actually designed to
> scale[1]
> >>> and are used as tools to scale the web too.
> >>>
> >>> This is all about the How question but when it comes to my
> original
> >>> Why, please correct me if I'm being wrong, the answer so far
> has been:
> >>> Pulp always downloads the content because that's what it is
> supposed to
> >>> do.
> >>>
> >>> Cheers,
> >>> milan
> >>>
> >>> [1] https://en.wikipedia.org/wiki/Reverse_proxy
> <https://en.wikipedia.org/wiki/Reverse_proxy>
> >>> [2]
> https://paste.fedoraproject.org/paste/zkBTyxZjm330FsqvPP0lIA
> <https://paste.fedoraproject.org/paste/zkBTyxZjm330FsqvPP0lIA>
> >>> [3]
> >>>
> https://wiki.squid-cache.org/Features/CacheHierarchy?highlight=%28faqlisted.yes%29
> <https://wiki.squid-cache.org/Features/CacheHierarchy?highlight=%28faqlisted.yes%29>
> >>>
> >>> >
> >>> >>
> >>> >>
> >>> >> Cheers,
> >>> >> milan
> >>> >>
> >>> >> >
> >>> >> > -dennis
> >>> >> >
> >>> >> >
> >>> >> >
> >>> >> >
> >>> >> >
> >>> >> >>
> >>> >> >>
> >>> >> >> --
> >>> >> >> cheers
> >>> >> >> milan
> >>> >> >>
> >>> >> >> On Tue, May 29, 2018 at 4:25 PM, Brian Bouterse
> >>> >> >> <bbouters at redhat.com <mailto:bbouters at redhat.com>>
> >>> >> >> wrote:
> >>> >> >> >
> >>> >> >> > On Mon, May 28, 2018 at 9:57 AM, Milan Kovacik
> >>> >> >> > <mkovacik at redhat.com <mailto:mkovacik at redhat.com>>
> >>> >> >> > wrote:
> >>> >> >> >>
> >>> >> >> >> Hi,
> >>> >> >> >>
> >>> >> >> >> Looking at the diagram[1] I'm wondering what's the
> reasoning
> >>> >> >> >> behind
> >>> >> >> >> Pulp having to actually fetch the content locally?
> >>> >> >> >
> >>> >> >> >
> >>> >> >> > Is the question "why is Pulp doing the fetching and
> not Squid?"
> >>> >> >> > or
> >>> >> >> > "why
> >>> >> >> > is
> >>> >> >> > Pulp storing the content after fetching it?" or both?
> >>> >> >> >
> >>> >> >> >> Couldn't Pulp just rely on the proxy with regards to
> the content
> >>> >> >> >> streaming?
> >>> >> >> >>
> >>> >> >> >> Thanks,
> >>> >> >> >> milan
> >>> >> >> >>
> >>> >> >> >>
> >>> >> >> >> [1] https://pulp.plan.io/attachments/130957
> <https://pulp.plan.io/attachments/130957>
> >>> >> >> >>
> >>> >> >> >> On Fri, May 25, 2018 at 9:11 PM, Brian Bouterse
> >>> >> >> >> <bbouters at redhat.com <mailto:bbouters at redhat.com>>
> >>> >> >> >> wrote:
> >>> >> >> >> > A mini-team of core devs** met to talk through lazy
> use cases
> >>> >> >> >> > for
> >>> >> >> >> > Pulp3.
> >>> >> >> >> > It's effectively the same lazy from Pulp2 except:
> >>> >> >> >> >
> >>> >> >> >> > * it's now built into core (not just RPM)
> >>> >> >> >> > * It disincludes repo protection use cases because
> we haven't
> >>> >> >> >> > added
> >>> >> >> >> > repo
> >>> >> >> >> > protection to Pulp3 yet
> >>> >> >> >> > * It disincludes the "background" policy which based on
> >>> >> >> >> > feedback
> >>> >> >> >> > from
> >>> >> >> >> > stakeholders provided very little value
> >>> >> >> >> > * it will no longer will depend on Twisted as a
> dependency. It
> >>> >> >> >> > will
> >>> >> >> >> > use
> >>> >> >> >> > asyncio instead.
> >>> >> >> >> >
> >>> >> >> >> > While it is being built into core, it will require
> minimal
> >>> >> >> >> > support
> >>> >> >> >> > by
> >>> >> >> >> > a
> >>> >> >> >> > plugin writer to add support for it. Details in the
> epic
> >>> >> >> >> > below.
> >>> >> >> >> >
> >>> >> >> >> > The current use cases along with a technical plan
> are written
> >>> >> >> >> > on
> >>> >> >> >> > this
> >>> >> >> >> > epic:
> >>> >> >> >> > https://pulp.plan.io/issues/3693
> <https://pulp.plan.io/issues/3693>
> >>> >> >> >> >
> >>> >> >> >> > We're putting it out for comment, questions, and
> feedback
> >>> >> >> >> > before
> >>> >> >> >> > we
> >>> >> >> >> > start
> >>> >> >> >> > into the code. I hope we are able to add this into
> our next
> >>> >> >> >> > sprint.
> >>> >> >> >> >
> >>> >> >> >> > ** ipanova, jortel, ttereshc, dkliban, bmbouter
> >>> >> >> >> >
> >>> >> >> >> > Thanks!
> >>> >> >> >> > Brian
> >>> >> >> >> >
> >>> >> >> >> >
> >>> >> >> >> > _______________________________________________
> >>> >> >> >> > Pulp-dev mailing list
> >>> >> >> >> > Pulp-dev at redhat.com <mailto:Pulp-dev at redhat.com>
> >>> >> >> >> > https://www.redhat.com/mailman/listinfo/pulp-dev
> <https://www.redhat.com/mailman/listinfo/pulp-dev>
> >>> >> >> >> >
> >>> >> >> >
> >>> >> >> >
> >>> >> >>
> >>> >> >> _______________________________________________
> >>> >> >> Pulp-dev mailing list
> >>> >> >> Pulp-dev at redhat.com <mailto:Pulp-dev at redhat.com>
> >>> >> >> https://www.redhat.com/mailman/listinfo/pulp-dev
> <https://www.redhat.com/mailman/listinfo/pulp-dev>
> >>> >> >
> >>> >> >
> >>> >
> >>> >
> >>>
> >>> _______________________________________________
> >>> Pulp-dev mailing list
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> >>> https://www.redhat.com/mailman/listinfo/pulp-dev
> <https://www.redhat.com/mailman/listinfo/pulp-dev>
> >>
> >>
> >>
> >> _______________________________________________
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> >>
> >
>
>
>
>
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