2. Zookeeper implementation of the cluster module using name space to support using same zookeeper cluster by different OAP clusters.

* Correct namespace description

* Support sampling trace at server side and keep metric right.

* Add a trace sampling document

* Fix wrong default value.

* Fix document issue.

* Fix assemble issue.

* Fix wrong settings and doc.

Also fixed several bugs in this merge.

* support set config from system.envs.

* Close the clients which are unreachable.
Remote client manager test case and comments.

* Test the GRPCRemote client.

* 1. Catch the throwable for onComplete method cause of it will throw exception when connection lost.
2. Check the gRPC channel state, send message when state is ready, wait 5 second when state is not ready.

Notice: gRPC channel getState with true parameter will trigger reconnect operation.

* gRPC client will reconnect to the server when network recorvered.

* Recovery application.yml

* Recovery proto module commit id.

* no message

* Fixed compile error.

* Change some codes to make zipkin receiver works, not done yet.

* @adriancole Zipkin receiver is coming back again.

* Fix document and fix for Zipkin receiver.

* Fix some bugs.

* Fix register bug.

* Fix transfer bug for new backend core.

* ZooKeeper Version Compatibility

* Update backend-cluster.md

Reorganize words. cc @peng-yongsheng

* Update application.yml

* Update application.yml

* H2 storage code skeleton.

* Add batch dao for H2.

* Fix wrong refactor.

* Add codes of other dao. No metric dao, wait for @peng-yongsheng new PR.

* Change license of distribution

* Add topology query in H2.

* Add more daos.

* Add some daos.

* Commit all H2 daos. Wait @peng-yongsheng to submit new IAggregationQueryDAO interface.

* Fix some CIs

* Fix wrong refactor, which causes h2 plugin failure.

* Fix all codes of H2 storage. :) and CI should pass. No test.

* Fix CI and typo

* Fix connection closed.

* Fix register bug

* no message

* Fixed service inventory register bug.

* Fix a compile issue.

* Sync change

* Reset es as default storage.

* Fix rat

* Fix H2 compile issue.

* Fix bugs for H2 storage.

* Fix bug in mesh.

* 1. Fix Thermodynamic query bug
2. Fix service inventory query bug
3. Fix missing traceid in trace query bug

* Fix query bug.

* Submit reverse caused by prev PR.

* Fix duplicate spans.

* Use H2 as default storage implementor.

* Fix bug in topology query.

* Fix CI

* Fix rat

* Fix two query in H2 storage.

* Fix H2 query

* Make release running in H2 mode and develop mode running is ES mode in default

* Make receiver more effective

* Add Istio test case and all source dispatch in

* Refactor mock data

* FIx rat.

* Support call component.

* Fix ThermodynamicIndicator bug.

* Fix test cases.

* Fix missing calculate in db merging.

* Add codes for debug.

* 1. Fixed elasticsearch bulk process not fresh bug. (#1819)

2. Fixed the bug of source register no queue but wait the end for batch tag.

* Remove debug log, and restore TTL timer for real scenarios.

* Support metrics downsampling.

* Fixed a check style error.

* Alarm query and alarm persistence test.

* Fixed the package error.

* Fixed the bug from topology.

* no message

* Add generate indicator and dispatcher about service topology but not test.

* Delete call type from service relation.

* Streaming analysis topology test success.

* Fixed the check style error.

* Fixed the startup failure cause by query protocol.

* Fixed the bug of startup failure.

* Buffer stream.

* Buffer file reader.

* Buffer library performance test and functional test successfully.

* Fixed the code merge mistake.

* SkyWalking's trace receiver implementation.

* SkyWalking's trace receiver implementation.

* Delete collector module.

Add a lot of documents. @peng-yongsheng @hanahmily . Also @hanahmily , the k8 cluster management document and deploy document need you to add.

* Register start up.

* Service inventory register test success.

* Storage and Persistence.

* Storage config.

* Fixed the CI failure.

# 1447
Use `GET /api/v1/watch/namespaces/{namespace}/pods` api to watch pod's
containerIp which help collector containers to discovery each other.

* Receiver, aggregate, server finished.

* Cluster module implementation finished.