Details
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New Feature
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Status: Done
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Major
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Resolution: Done
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None
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None
Description
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.
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