Define ScyllaDB as drop-in replacement for Cassandra

[mkorolyov]

Which problem is this PR solving?

Defines that Jaeger server supports ScyllaDB as a storage backend as a drop-in replacement for Cassandra

Short description of the changes

Updated README.md

[mkorolyov]

i can provide a demo docker-compose file but have no idea where to place it to make it easily discoverable by the community

[yurishkuro]

We can add a folder plugins/storage/scylladb with a README and a docker-compose file. The README can call out any relevant details (or any differences vs. Cassandra). But I would like to have a clear disclaimer at the top that this is not an officially supported backend, meaning that we will not proactively address any issues that may arise from incompatibilities between the two databases (we may still accept PRs).

[yurishkuro]

Please make sure all commits are signed (or squash into one and sign).

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 ⚠️

Comparison is base (bc8e1d1) 97.10% compared to head (bfbace7) 97.10%.

Additional details and impacted files

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##             main    #4353      +/-   ##
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- Coverage   97.10%   97.10%   -0.01%     
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  Files         300      300              
  Lines       17697    17697              
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- Hits        17185    17184       -1     
- Misses        412      413       +1     
  Partials      100      100              

Flag	Coverage Δ
unittests	97.10% <ø> (-0.01%)	⬇️

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see 1 file with indirect coverage changes

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[yurishkuro]

lgtm, but please make sure commits are signed (see CONTRIBUTING.md)

[yurishkuro]

Sounds like maybe there should be a config param in Jaeger to set the version explicitly instead of sniffing it.

[mkorolyov]

i have tried both

      CASSANDRA_PROTOCOL_VERSION: 4
      CASSANDRA_VERSION: 4

but nothing helped. It depects the version from interaction with ScyllaDB

[yurishkuro]

few small improvements

[mkorolyov]

Hi @yurishkuro
Thanks for the review. I reworked health checks and simplified things a lot. Also, I applied all the style nits you posted above.

I still use docker compose up -d instead of the suggested docker compose up because without background mode console is filled with tons of logs from 3 ScyllaDB nodes communicating with each other to gather into a single cluster and even after that it is not obvious that you can start using HotRod or JaegerUI. While with background mode it is transparent that ScyllaDB is starting for some time and then all other containers are spinning up and you can try JaegerUI or HotRod.

[yurishkuro]

Thanks. One possible minor improvement is to pull the Jaeger and ScyllaDB versions into variables at the top of the compose file.