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From "Uwe Schindler" <...@thetaphi.de>
Subject RE: SolrCloud Alone: Deprecate Standalone Mode
Date Thu, 12 Aug 2021 11:09:29 GMT
I am fully happy with something that works out of box.

 

The main problems I see with many customers is not only the complexity of setup, but also
that you need to install a separate Zookeeper ensemble. When you tell them: Come on, use the
one provided by a solr node and you are fine: “no this is not allowed, see doc xy”.

 

So let us please simplify the recommendations: If you have one or 2 or three nodes in standalone
node, it is perfectly fine to use embedded zookeeper. We should not overreact here. A user
who used Master/Slave replication is also not fully fault tolerant.

 

I’d change the documentation to say something: “If you want to scale, use a separate zookeeper
ensemble with a minimum of three nodes. But for simple setups just relying on the good old
master/slave replication (not the default solr one that distributes indexing), it is perfectly
fine to use embedded zookeeper (on the “master” node that holds the main index). This
setup is then not really different from classical master/slave replication.

 

As said before, I am not against Solr cloud, but lets keep it simple for people that want
to keep it simple. I am also fine to start a single node cluster with zookeeper, but this
should be the embedded one (just as datastore for the fake cluster). And no warnings should
be printed. Maybe as soon as you add too many nodes, print some warning “now it is time
to setup a separate zookeeper ensemble”. But, please not for 2 nodes (master/slave).

 

Also where is the problem in spawning an embedded zookeeper in every node by default? Why
does it need to be separated?

 

Uwe

 

-----

Uwe Schindler

Achterdiek 19, D-28357 Bremen

https://www.thetaphi.de

eMail: uwe@thetaphi.de

 

From: Jan Høydahl <jan.asf@cominvent.com> 
Sent: Wednesday, August 11, 2021 4:27 PM
To: dev@solr.apache.org
Subject: Re: SolrCloud Alone: Deprecate Standalone Mode

 

However, we tell people not to use the embedded ZK in production, so I’m curious if that’s
only because it’s a single-node ZK or if there is something else about the way we’ve embedded
it that we would need to change?

 

As I recall there are several reasons. First, our embedded ZK was kind of a hack with some
forked code etc. Second, it is not designed to be fault tolerant even if you start three solr
nodes this way we cannot form a quorum. And perhaps third, ZK has not been officially supported
on Windows.. However, I believe this is all solvable if we want to day. Not saying it is easy
though :) 

 

Jan





11. aug. 2021 kl. 16:17 skrev Cassandra Targett <casstargett@gmail.com <mailto:casstargett@gmail.com>
>:

 

So basically the proposal would be that we use the embedded ZK to automatically create a quorum
via multiple nodes. That’s an interesting idea.

However, we tell people not to use the embedded ZK in production, so I’m curious if that’s
only because it’s a single-node ZK or if there is something else about the way we’ve embedded
it that we would need to change?

I was also under the impression that beyond the complexities of ZK there are still use cases
that SolrCloud does not adequately support, even with the addition of TLOG and PULL replicas.
Does anyone have any examples of those?

I’d also like to remind folks to please not use the terminology “master/slave”, we removed
it from the code and documentation because it’s not inclusive for our community. 

Similarly, “standalone” has always been rather imprecise - it’s not “standalone”,
it’s a cluster but without ZK and other automation sugar. In the Ref Guide we’ve settled
on “user-managed”. It sounds pedantic but it matters because we should be really clear
about what we’re talking about - deprecating and removing the ability for a single-node
Solr installation? Only the mode of a non-ZK cluster? Both?

On Aug 11, 2021, 6:39 AM -0500, Eric Pugh <epugh@opensourceconnections.com <mailto:epugh@opensourceconnections.com>
>, wrote:



For small setups I’ve used a single ZK and a single Solr node very successfully, the operational
benefits of all the SolrCloud API’s has been fantastic. 

 

I’ve always thought that us having ZooKeeper as this “front and center” requirement
for SolrCloud was always a weird decision that would put off a lot of folks.   We don’t
beat our potential users over the head with the fact we use Jetty for example.   It’s just
part of the stack.   

 

The flow that Gus proposed should have been added to SolrCloud a long time ago, how much easier
would it have made all our lives!   The entire existence of ZooKeeper should be behind APIs
and be an abstraction.  We should do this regardless of if deprecated standalone!

 

Uwe, if we had what Gus proposed, but eliminate zk, would that map much more to what you wanted?
 Here is my attempt at retelling the story that Gus told, but to meet the goals of folks who
might want to move to ES for ease:

 

A) Start Node 1.
B) Start Node 2 telling it that Node 1 exists. node 2 comes up, joins network and messages
“at risk for split brain”.
C) Start Node 3 telling it that node 1 exists. node 1, node 2, node 3 all under the covers
are sharing state via ZK and messages “no risk for split brain"
D) Node 4 - like node 2 but since we have optimum quorum doesn’t add to ZK (under covers,
hidden from user).
E) Node 5 - like node 3, but since we have optimum quorum doesn’t add to ZK (under covers,
hidden from user).

 

 

 

 





On Aug 11, 2021, at 7:15 AM, Uwe Schindler <uwe@thetaphi.de <mailto:uwe@thetaphi.de>
> wrote:

 

Hi,

 

most of my customers prefer standalone mode and manual replication. A lot of setups, especially
in Germany, are very 

 

Solr Cloud is only interesting to large customers that want to scale hugely. But from what
I have seen, most of those have moved to Elasticsearch or Opensearch (see below). The biggest
issue is always the stupidness of having to maintain a separate Zookeeper cloud, which adds
more hardware/VMs to the game and makes the thing more complex. If you want to maintain up
to 4 or 6 Solr nodes with one index and a few shards, the overhead by Zookeeper (you need
3 of them) is – sorry to say – unmaintainable. With Elasticsearch it’s easy to setup.
No dedicated cloud/standalone mode. You just start a single node and test it. If it works
fine, you start additional nodes to form a cloud. Plain simple. Config files are easy to handle,
you need no ip addresses hardcoded into Zookeeper nodes, it just works. If you don’t want
to make people move to Elasticsearch/Opensearch, make them happy with their fully controllable
local master/slave mode.

 

So my strong -1 to make cloud mode the default and deprecate standalone mode. Unless both
is the same and works without a separate zookeeper cluster, I won’t change my vote.

 

Uwe

 

-----

Uwe Schindler

Achterdiek 19, D-28357 Bremen

https://www.thetaphi.de <https://www.thetaphi.de/> 

eMail: uwe@thetaphi.de <mailto:uwe@thetaphi.de> 

 

From: Gus Heck <gus.heck@gmail.com <mailto:gus.heck@gmail.com> > 
Sent: Tuesday, August 10, 2021 8:34 PM
To: dev@solr.apache.org <mailto:dev@solr.apache.org> 
Subject: Re: SolrCloud Alone: Deprecate Standalone Mode

 

Or to keep things fast without retaining all the checks, one could provide slow/fast modes
for test, fast requiring a local zookeeper external to the tests, with the tests properly
namespacing themselves... that does imply reworking some tests. 

 

Now that I say the above, it would be interesting if the some of the tests could (also optionally)
properly isolate themselves within an externally running solr (probably started via cloud.sh
with the latest edits. ... develop, cloud.sh, test manually, run tests against same I expect
that there are still tests for which that makes no sense of course. This is probably a crazier
idea than using an external zookeeper however, where zkChroot should be sufficient to isolate
things I think...

 

-Gus

 

On Tue, Aug 10, 2021 at 2:22 PM David Smiley <dsmiley@apache.org <mailto:dsmiley@apache.org>
> wrote:

Good call-out on perceived complexity due to running 3 ZK nodes.  For many small installations,
honestly Solr's embedded ZK is fine.  Also, again for small installations, running ZK alongside
Solr (same hardware) is fine.  We shouldn't needlessly shame users away from doing these things
as if it's irresponsible.  There's a spectrum of demands on Solr from low to high.  Anyway,
I suspect it's increasingly moot with more Docker & Kubernetes being used to reduce the
hassles of deploying any service (be it Solr or whatever).  This will only increase going
forward.

 

Even if ZK becomes the only mode, I expect many checks in our codebase that conditionally
check for ZK to remain.  We want tests that don't care about SolrCloud mode to be fast, and
that means not running unnecessary things like ZooKeeper.




~ David Smiley

Apache Lucene/Solr Search Developer

http://www.linkedin.com/in/davidwsmiley

 

 

On Tue, Aug 10, 2021 at 12:23 PM Gus Heck <gus.heck@gmail.com <mailto:gus.heck@gmail.com>
> wrote:

I've met several clients who really didn't want to manage zookeeper as an additional service
(I've talked some into it anyway, but it was clearly a key reason they hadn't started/gone
cloud). I think it would be far more palatable if it's all "part of solr", doesn't require
plumbing the docs of some other project entirely, and requires neither requisitioning additional
hardware nor service scripts, monitoring, support that isn't "solr" support... etc... then
I think that alleviates some of the pain that folks in small sub-sections of moderate to large
orgs feel at the idea of using cloud. These folks face long procurement cycles and disaster/recovery
plans etc, despite often having team sizes under 20... or face having to educate large IT
departments into handling deployments when they themselves are new (of course that's how some
of them wind up hiring folks like me... but that's a barrier too since that has to be approved
too).  Also I've met folks who didn't understand that it was possible to have a 1 node "cluster"
with zk on the same machine, and had the impression that 5 boxes (2 solr and 3 zk) were absolutely
required to run cloud. Which it is of course for high availability with no SPOF, but it is
not required if you don't need high availability. 

 

I think to sunset "user managed" we need to figure out how to self manage embedded zookeepers,
most particularly setup for smaller orgs or lower traffic installs should look like:

 

A) Start Node 1 with zk embedded ... if you only need one node, don't want high availability
etc, done.

B) Start Node 2 telling it the zk url for node 1. node 2 comes up, offers to participate in
zk, but does not because that would make an even number

C) Start Node 3 telling it the zk url for node 1. node 1 (node 2 hasn't started zk) node 3
offers to participate in zk, and now with 2 offers pending, both 2 and 3, get up to date on
the current state and th join, now the embedded zk cluster is 3 nodes, not one, and no SPOF...
as they grow...

D) Node 4 - like node 2 but can use zk url of any of 1,2,3

E) Node 5 - like node 3, but can use zk url of any 1,2,3

 

Obviously, features for users to set a cap the size of zk clusters, don't need 49 nodes on
50 servers... , ensure they put their data in a convenient place that is well documented,
document how to secure the inter-node connections, clarity in the admin UI of what nodes have
zk etc. 

 

For this embedded zk use case we should document whatever the user needs to know so they don't
have to sort through docs at an entirely different project not necessarily focused on the
things solr users need.

 

Certainly we would still advocate for a separate zk cluster for better performance/stability.
In essence a supported mode with known limitations... True we have to support all THAT code
instead, but the available feature set becomes consistent and a bazillion checks to see if
we have zkStateReader (or some other sentinel for cloud mode) can disappear, so probably a
net gain etc.

 

On the flip side I"ve also had the thought that cluster state management should be pluggable
such that if a better tool than zk, or merely an "already installed" tool is available solr
could use it. Without careful thought everything I just said could take us in the opposite
direction

 

Maybe running zk embedded is "Solr Fog" mode :) 

 

On Mon, Aug 9, 2021 at 2:55 PM Houston Putman <houstonputman@gmail.com <mailto:houstonputman@gmail.com>
> wrote:

I agree with David that the first step would be to make SolrCloud the default mode.

I made a dev list thread about this a few months ago, but I think I failed to respond at some
point.

I will get back on that and address the 

 

I also really like Mike's idea that we enable very similar use cases with embedded Zookeeper's,

if at all possible, to make the transition easy for users who want to stay on the user-manager
mode.

 

Marcus, I think it would be a great idea to fix up the documentation to make SolrCloud the
first and most prominent mode advertised.

Never saw your original PR, but would love to give it a look if you resuscitate it at some
point.

 

- Houston

 

On Mon, Aug 9, 2021 at 2:48 PM David Smiley <dsmiley@apache.org <mailto:dsmiley@apache.org>
> wrote:

Given that SolrCloud is not even the default mode, I think it is premature to deprecate standalone
mode.  Let's do this first and maybe consider deprecating standalone after some time?




~ David Smiley

Apache Lucene/Solr Search Developer

http://www.linkedin.com/in/davidwsmiley

 

 

On Mon, Aug 9, 2021 at 1:58 PM Mike Drob <mdrob@mdrob.com <mailto:mdrob@mdrob.com>
> wrote:

Could we simulate user managed replication with an embedded zookeeper
on the primary and pull replicas on the followers?

On Mon, Aug 9, 2021 at 12:56 PM Jason Gerlowski <gerlowskija@gmail.com <mailto:gerlowskija@gmail.com>
> wrote:
>
> Hey Marcus,
>
> The places I've worked in the past have all used SolrCloud primarily
> so I can't speak to any specifics, but my impression from reading
> user-list traffic is that a sizable chunk of Solr's user base prefers
> "User-Managed" mode (formerly called "standalone").  Some because they
> don't want to manage a ZooKeeper cluster.  Some because the
> replication model in 'user-managed' fits their needs better.  Some I
> imagine just haven't bothered to update in many years.
>
> I'm absolutely sympathetic to efforts to streamline development and
> reduce collective debt, but it might be tough to displace such a big
> chunk of users.  I'm curious what others think though.  Maybe the
> proportion of 'user-managed' users out there is smaller than I
> imagine.
>
> Jason
>
> On Fri, Aug 6, 2021 at 11:59 PM Marcus Eagan <marcuseagan@gmail.com <mailto:marcuseagan@gmail.com>
> wrote:
> >
> > Hello again,
> >
> > Has the time come for us to reduce scope to move faster and with more focus? Even
for those not in the cloud, SolrCloud has been the undisputed performance and usability champ
since version 8.0. In version 9.0, I'd like to propose that the deciders in the community
deprecate standalone mode in favor of SolrCloud.
> >
> > There are a few drivers:
> >
> > We only need to support changes that impact SolrCloud going forward. I know that
this is hard to stomach. But by the time Solr reaches version 10.0, everyone should have migrated
to SolrCloud as there is little reason to continue to run standalone.
> > The new features keep coming to SolrCloud, but not to standalone. You can see in
a few ways how I embarrassingly discovered this late one night while trying out a PR. If not
careful, users can accidentally start Solr in standalone mode. Think of all the features that
they will see documented but not in their environment. What a confusing user experience?
> > Last but certainly not least, the number of contributors to the project, and the
velocity of those contributions has dropped. . It does not have to be that way, though. Two
ways are for the community to observe our push for modernization and improved user experience.
Simply eliminating the need to include the -c flag in the start command would be a huge win
for many engineers.We should make life easier for our users as much as the maintainers here.
We can strive to make the upgrade process from 9 to 10 very simple.
> >
> > I tried to make one step in this direction last year by re-ordering the README to
show the Solr Cloud command before the standalone command. I believe that patch died on the
vine, but I would be excited to revive it to document this effort when the time is appropriate.
> >
> > Reason not to do it:
> >
> >  Some large company out there might view this move as introducing risk. I view the
risk here as negligible but I welcome any perspective there.
> > Some things I inevitably don't know.
> >
> > What do you all think?
> >
> > Thank you all for your voluntary contributions,
> > --
> > Marcus Eagan
> >
>
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