Deprecate tchannel

[objectiser]

Signed-off-by: Gary Brown gary@brownuk.com

Which problem is this PR solving?

Deprecating tchannel so can be removed from future release.

Short description of the changes

Added deprecation notice to agent flag and collector/all-in-one handler.

[codecov]

Codecov Report

Merging #1975 into master will decrease coverage by 0.01%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #1975      +/-   ##
==========================================
- Coverage   96.99%   96.97%   -0.02%     
==========================================
  Files         203      203              
  Lines       10062    10064       +2     
==========================================
  Hits         9760     9760              
- Misses        264      265       +1     
- Partials       38       39       +1

Impacted Files	Coverage Δ
cmd/agent/app/reporter/flags.go	68.75% <33.33%> (-9.83%)	⬇️

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[pavolloffay]

It might be also better to add deprecated annotation to all tchannel flags:

      --reporter.tchannel.discovery.conn-check-timeout duration   sets the timeout used when establishing new connections (default 250ms)
      --reporter.tchannel.discovery.min-peers int                 if using service discovery, the min number of connections to maintain to the backend (default 3)
      --reporter.tchannel.host-port string                        comma-separated string representing host:ports of a static list of collectors to connect to directly (e.g. when not using service discovery)
      --reporter.tchannel.report-timeout duration                 sets the timeout used when reporting spans (default 1s)

The deprecation message in reporter type is not that obvious

--reporter.type string                                      Reporter type to use e.g. grpc, tchannel[NOTE: Deprecated since 1.16] (default "grpc")

Like

      --discovery.conn-check-timeout duration                     (deprecated) see --reporter.tchannel.discovery.conn-check-timeout (default 250ms)
      --discovery.min-peers int                                   (deprecated) see --reporter.tchannel.discovery.min-peers (default 3)

[objectiser]

@pavolloffay Agree the other tchannel flags would be better deprecated.

However reporter.type is difficult, because we are not deprecating that parameter, only one of its values.

[KeaMedes]

could someone explain why tchannel is deprecated?

[pavolloffay]

We have decided to use gRPC instead. IIRC tchannel also does not properly support load balancing (at least in k8s environment).