[Pulp-dev] Lazy for Pulp3

Wed May 30 14:50:52 UTC 2018

On Wed, May 30, 2018 at 8:57 AM, Tom McKay <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.

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). Is that right?

>
> [1] https://github.com/candlepin/thumbslug
>
> On Wed, May 30, 2018 at 8:34 AM, Milan Kovacik <mkovacik at redhat.com>
> wrote:
>
>> On Tue, May 29, 2018 at 9:31 PM, Dennis Kliban <dkliban at redhat.com>
>> wrote:
>> > On Tue, May 29, 2018 at 11:42 AM, Milan Kovacik <mkovacik at redhat.com>
>> wrote:
>> >>
>> >> On Tue, May 29, 2018 at 5:13 PM, Dennis Kliban <dkliban at redhat.com>
>> wrote:
>> >> > On Tue, May 29, 2018 at 10:41 AM, Milan Kovacik <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
>> [2] https://paste.fedoraproject.org/paste/zkBTyxZjm330FsqvPP0lIA
>> [3] https://wiki.squid-cache.org/Features/CacheHierarchy?highlig
>> ht=%28faqlisted.yes%29
>>
>> >
>> >>
>> >>
>> >> Cheers,
>> >> milan
>> >>
>> >> >
>> >> > -dennis
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >>
>> >> >>
>> >> >> --
>> >> >> cheers
>> >> >> milan
>> >> >>
>> >> >> On Tue, May 29, 2018 at 4:25 PM, Brian Bouterse <
>> bbouters at redhat.com>
>> >> >> wrote:
>> >> >> >
>> >> >> > On Mon, May 28, 2018 at 9:57 AM, Milan Kovacik <
>> 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
>> >> >> >>
>> >> >> >> On Fri, May 25, 2018 at 9:11 PM, Brian Bouterse
>> >> >> >> <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
>> >> >> >> >
>> >> >> >> > 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
>> >> >> >> > https://www.redhat.com/mailman/listinfo/pulp-dev
>> >> >> >> >
>> >> >> >
>> >> >> >
>> >> >>
>> >> >> _______________________________________________
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>> >> >> https://www.redhat.com/mailman/listinfo/pulp-dev
>> >> >
>> >> >
>> >
>> >
>>
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