> Ilan: A node not having node.roles defined should be assumed to have all
roles. Not only data. I don't see a reason to special case this one or any
role.
> Gus: There should be no "assumptions" Nothing to figure out. A node has a
role or not. For back compatibility reasons, all roles would be assumed on
startup if none specified.
> Jan: No role == all roles. Explicit list of roles = exactly those roles.
Problem with this approach is mainly to do with backcompat.
*1. Overseer backcompat:*
If we don't make any modifications to how overseer works and adopt this
approach (as quoted), then imagine this situation:
Solr1-100: No roles param (assumed to be "data,overseer").
Solr101: -Dnode.roles=overseer (intention: dedicated overseer)
User wants this node Solr101 to be a dedicated overseer, but for that to
happen, he/she would need to restart all the data nodes with
-Dnode.roles=data. This will cause unnecessary disruption to running
clusters where a dedicated overseer is needed. Keep in mind, if a user
needs a dedicated overseer, he's likely in an emergency situation and
restarting the whole cluster might not be viable for him/her.
*2. Future roles might not be compatible with this "assumed to have all
roles" idea:*
Take the proposed "zookeeper" role for example. Today, regular nodes are
not supposed to have embedded ZK running on them. By introducing this
artificial limitation ("assumed to have all roles"), we constrain adoption
of all future roles to necessarily require a full cluster restart.
Keep in mind newer Solr versions can introduce new capabilities and roles.
Imagine we have a role that is defined in a new Solr version (and there's
functionality to go with that role), and user upgrades to that version.
However, his/her nodes all were started with no node.roles param. Hence, if
those nodes are "assumed to have all roles", then just by virtue of
upgrading to this new version, new capabilities will be turned on for the
entire cluster, whether or not the user opted for such a capability. This
is totally undesirable.
> Gus: I actually don't want a coordinator to do more work, I would prefer
small focused roles with names that accurately describe their function. In
that light, COORDINATOR might be too nebulous. How about AGREGATOR role?
(what I was thinking of would better be called a QUERY_ANALYSIS role)
If you want to do specific things like query analysis or query aggregation
or bulk indexing etc, all of those can be done on COORDINATOR nodes (as is
the case in ElasticSearch). Having tens of of " small focused roles"
defined as first class concepts would be confusing to the user. As a remedy
to your situation where you want the coordinator role to also do
query-analysis for shards, one possible solution is to send such a query to
a coordinator node with a parameter like "coordinator.query_analysis=true",
and then the coordinator, instead of blindly hitting remote shards, also
does some extra work on behalf of the shards.
On Mon, Nov 1, 2021 at 9:01 PM Ishan Chattopadhyaya <
ichattopadhy...@gmail.com> wrote:
> > If we make collections role-aware for example (replicas of that
> collection can only be
> > placed on nodes with a specific role, in addition to the other role
> based constraints),
> > the set of roles should be user extensible and not fixed.
> > If collections are not role aware, the constraints introduced by roles
> apply to all collections
> > equally which might be insufficient if a user needs for example a
> heavily used collection to
> > only be placed on more powerful nodes.
>
> I feel node roles and role-aware collections are orthogonal topics. What
> you describe above can be achieved by the autoscaling+replica placement
> framework where the placement plugins take the node roles as one of the
> inputs.
>
> > It does impact the design from early on: the set of roles need to be
> expandable by a user
> > by creating a collection with new roles for example (consumed by
> placement plugins) and be
> > able to start nodes with new (arbitrary) roles. Should such roles follow
> some naming syntax to
> > differentiate them from built in roles? To be able to fail on typos on
> roles - that otherwise can be
> > crippling and hard to debug. This implies in any case that the current
> design can't assume all
> > roles are known at compile time or define them in a Java enum.
>
> I think this should be achieved by something different from roles.
> Something like node *labels* (user defined) which can then be used in a
> replica placement plugin to assign replicas. I see roles as more closely
> associated with kinds of functionality a node is designated for. Therefore,
> I feel that replica placements and user defined node labels is out of scope
> for this SIP. It can be added later in a separate SIP, without being at
> odds with this proposal.
>
>
>
>
>
>
> On Mon, Nov 1, 2021 at 8:42 PM Jan Høydahl <jan....@cominvent.com> wrote:
>
>>
>>
>> > 1. nov. 2021 kl. 14:46 skrev Ilan Ginzburg <ilans...@gmail.com>:
>> > A node not having node.roles defined should be assumed to have all
>> roles. Not only data. I don't see a reason to special case this one or any
>> role.
>>
>> +1, make it simple and transparent. No role == all roles. Explicit list
>> of roles = exactly those roles.
>>
>> > (Gus) See my comment above, but maybe preference is something handled
>> as a feature of the role rather than via role designation?
>>
>> Yea, we always need an overseer, so that feature can decide to use its
>> list of nodes as a preference if it so chooses.
>>
>>
>> Aside: I think it makes it easier if we always prefix Solr env.vars and
>> sys.props with "SOLR_" or "solr.", i.e. -Dsolr.node.roles=foo. That way we
>> can get away from having to have explicit code in bin/solr, bin/solr.cmd
>> and SolrCLI to manage every single property. Instead we can parse all ENVs
>> and Props with the solr prefix in our bootstrap code. And we can by
>> convention allow e.g. docker run -e SOLR_NODE_ROLES=foo solr:9 and it would
>> be the same ting...
>>
>> Jan
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