Jan, so if my world doesn't include Kubernetes, it would be a reasonable
addition to Solr to ship a placement plugin that scales up and down the single
shard collections that use it. And does the book keeping in ZooKeeper to not
show down nodes or down replicas?
Not sure how complex the engineering on this will be!
Out of curiosity, why would scaling down to 1 and back up to N not be an
already supported pattern? Is it because everyone does that with their own
scripts external to Solr or via the Operator? What am I missing about this use
case?
On Thursday, March 12, 2026 at 08:27:15 AM EDT, David Eric Pugh
<[email protected]> wrote:
David --> I oddly struggled to write the email cause I was stumbling over my
words... I wasn't sure if I should have said "shard", and how to phrase a
collection made up of a single core.... And then copies of that core...
After I read your response, I thought, I should check out the Solr Concepts
page and see what it tells me and discovered that we have nothing under Solr
Concepts specific to this topic. I looked up in the glossary "SolrCloud" and
it led me to
https://solr.apache.org/guide/solr/latest/deployment-guide/cluster-types.html#solrcloud-mode.
Only later when I scrolled up in the page did I see the section "Cluster
Concepts". Thoughts on maybe moving that section under the Solr Concepts
hierarchy in Ref Guide? It would have helped me use the right terms!
On Wednesday, March 11, 2026 at 06:38:17 PM EDT, David Smiley
<[email protected]> wrote:
An aside: Remember that the leader is a replica too, so your numbers are
off & confusing. "single shard with no replicas" -- I guessed what you
mean but surprised to hear a misuse of SolrCloud lingo from you. AFAICT,
leadership isn't even pertinent to your inquiry either.
On Wed, Mar 11, 2026 at 5:38 PM David Eric Pugh via dev <[email protected]>
wrote:
> Hey all, I wanted to get some feedback from you'all on a recent usecase I
> was asked about. I suspect the answer will be "Use Solr Operator", but
> here goes!
> I have an environment where I have 5 or so single shard collections.
> Much of the time I run just a single node and each collection is a single
> shard with no replicas. Sometimes, to support load, I'll add another node
> or two. Then I'll add replicas so cover the new nodes, 1 per node. So
> with three nodes, I have one leader and two replicas. Add two more nodes,
> move to one leader and four replicas.
> However, when I remove a node by shutting it down, then Zookeeper never
> get's notified about this, and so the replica is listed as down, and the
> node is listed as down in red in the UI. When it isn't really red, it's
> just we don't need it for now, and it's not coming back.
> I'd like to just declare "For this collection, I want one replica per node
> based on however many nodes are current". I don't want to call the
> various commands myself to add replicas and or remove then as nodes are
> added or removed. And I don't want to call various apis or other complex
> things when I add or remove a node, I just want bin/solr stop and bin/solr
> start to be run ;-).
> I think this is what Replica Placement Plugins were for maybe? Could I
> have a Replica Placement strategy that when ZK sees a new node added, then
> creates a new replica on it, and vice versa, when a node goes away, it just
> removes that replica instead of treating it as "down"?
> Thoughts?
> Eric
>
