GitHub user cestella opened a pull request:
https://github.com/apache/metron/pull/940
Single bolt split join poc
## Contributor Comments
There are some deficiencies to the split/join topology.
It's hard to reason about
* Understanding the latency of enriching a message requires looking at
multiple bolts that each give summary statistics
* The join bolt's cache is really hard to reason about when performance
tuning
* During spikes in traffic, you can overload the join bolt's cache and drop
messages if you aren't careful
* In general, it's hard to associate a cache size and a duration kept in
cache with throughput and latency
* There are a lot of network hops per message
* Right now we are stuck at 2 stages of transformations being done
(enrichment and threat intel). It's very possible that you might want stellar
enrichments to depend on the output of other stellar enrichments. In order to
implement this in split/join you'd have to create a cycle in the storm topology
I propose that we move to a model where we do enrichments in a single bolt
in parallel using a static threadpool (e.g. multiple workers in the same
process would share the threadpool). IN all other ways, this would be
backwards compatible. A transparent drop-in for the existing enrichment
topology.
There are some pros/cons about this too:
* Pro
* Easier to reason about from an individual message perspective
* Architecturally decoupled from Storm
* This sets us up if we want to consider other streaming technologies
* Fewer bolts
* spout -> enrichment bolt -> threatintel bolt -> output bolt
* Way fewer network hops per message
currently 2n+1 where n is the number of enrichments used (if using stellar
subgroups, each subgroup is a hop)
* Easier to reason about from a performance perspective
* We trade cache size and eviction timeout for threadpool size
* We set ourselves up to have stellar subgroups with dependencies
i.e. stellar subgroups that depend on the output of other subgroups
If we do this, we can shrink the topology to just spout ->
enrichment/threat intel -> output
* Con
* We can no longer tune stellar enrichments independent from HBase
enrichments
* To be fair, with enrichments moving to stellar, this is the case in
the split/join approach too
* No idea about performance
What I propose is to submit a PR that will deliver an alternative,
completely backwards compatible topology for enrichment that you can use by
adjusting the `start_enrichment_topology.sh` script to use
`remote-unified.yaml` instead of `remote.yaml`. If we live with it for a while
and have some good experiences with it, maybe we can consider retiring the old
enrichment topology.
To test this, spin up vagrant and edit
`$METRON_HOME/bin/start_enrichment_topology.sh` to use `remote-unified.yaml`
instead of `remote.yaml`. Restart enrichment and you should see a topology
that looks something like:
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#### Note:
Please ensure that once the PR is submitted, you check travis-ci for build
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You can merge this pull request into a Git repository by running:
$ git pull https://github.com/cestella/incubator-metron
single_bolt_split_join_poc
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/metron/pull/940.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #940
----
commit a4f618a3ad895d62772366e0e93e5b8b37c5c964
Author: cstella <cestella@...>
Date: 2018-02-21T23:59:16Z
Adding parallel enrichment bolt.
commit 99fe0b86005fe04294b3851a17ae3d88f228c5d2
Author: cstella <cestella@...>
Date: 2018-02-22T00:21:06Z
Updating to include trace statements.
commit 79736c6f3fab04d01dd1eb998b308f438003a0e1
Author: cstella <cestella@...>
Date: 2018-02-22T15:35:44Z
Updating with some cleanup
commit cb4a527c9146865dafad1d597ba93032ef398d94
Author: cstella <cestella@...>
Date: 2018-02-22T15:48:11Z
Updating spec.
commit fb4d4383f366776f446e33a422652c3ec1f56bfa
Author: cstella <cestella@...>
Date: 2018-02-22T18:00:36Z
Updating threadpool creation
commit 87ef6a72827c31f8adee42ee71272a32c350bc1f
Author: cstella <cestella@...>
Date: 2018-02-22T18:04:37Z
better docs
----
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