Use the HealthCheckImpl in vtctld instead of the LegacyHealthCheck

[frouioui]

Description

This Pull Request removes the usage of the legacy healthcheck in the vtctld package. The new healthcheck implementation is used instead.

In the vtctld API, instead of having a realtime_stats and tablet_cache, we now only have a healthcheck implementation. Most of the code that lived in realtime_stats and tablet_cache and that was required by the new implementation got moved to api_utils.go

Related Issue(s)

• part of Task: delete deprecated discoverygateway and legacy healthcheck code #9218
• fixes Task: change vtctld's realtime_status to use new health check #9358

Checklist

• "Backport me!" label has been added if this change should be backported
• Tests were added or are not required
• Documentation was added or is not required

[github-actions]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has the correct release notes label. release notes none should only be used for PRs that are so trivial that they need not be included.
• If a new flag is being introduced, review whether it is really needed. The flag names should be clear and intuitive (as far as possible), and the flag's help should be descriptive.

Bug fixes

• There should be at least one unit or end-to-end test.
• The Pull Request description should either include a link to an issue that describes the bug OR an actual description of the bug and how to reproduce, along with a description of the fix.

Non-trivial changes

• There should be some code comments as to why things are implemented the way they are.

New/Existing features

• Should be documented, either by modifying the existing documentation or creating new documentation.
• New features should have a link to a feature request issue or an RFC that documents the use cases, corner cases and test cases.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• vtctl command output order should be stable and awk-able.

[frouioui]

Manual Testing

Here is a preview of a couple of endpoints before and after the changes brought by this PR. Other endpoints have been manually tested too on both sharded and unsharded clusters, nothing to report.

http://localhost:15000/api/tablet_health/zone1/100

Before

{
  "Key": "localhost,grpc:16100,vt:15100",
  "Tablet": {
    "alias": {
      "cell": "zone1",
      "uid": 100
    },
    "hostname": "localhost",
    "port_map": {
      "grpc": 16100,
      "vt": 15100
    },
    "keyspace": "commerce",
    "shard": "0",
    "type": 1,
    "mysql_hostname": "localhost",
    "mysql_port": 17100,
    "primary_term_start_time": {
      "seconds": 1653685533,
      "nanoseconds": 104635000
    },
    "db_server_version": "8.0.28",
    "default_conn_collation": 255
  },
  "Name": "zone1-0000000100",
  "Target": {
    "keyspace": "commerce",
    "shard": "0",
    "tablet_type": 1
  },
  "Up": true,
  "Serving": true,
  "TabletExternallyReparentedTimestamp": 1653685533,
  "Stats": {},
  "LastError": null
}

After

{
  "Key": "localhost,grpc:16100,vt:15100",
  "Tablet": {
    "alias": {
      "cell": "zone1",
      "uid": 100
    },
    "hostname": "localhost",
    "port_map": {
      "grpc": 16100,
      "vt": 15100
    },
    "keyspace": "commerce",
    "shard": "0",
    "type": 1,
    "mysql_hostname": "localhost",
    "mysql_port": 17100,
    "primary_term_start_time": {
      "seconds": 1653686352,
      "nanoseconds": 49835000
    },
    "db_server_version": "8.0.28",
    "default_conn_collation": 255
  },
  "Name": "zone1-0000000100",
  "Target": {
    "keyspace": "commerce",
    "shard": "0",
    "tablet_type": 1
  },
  "Up": true,
  "Serving": true,
  "PrimaryTermStartTime": 1653686352,
  "TabletExternallyReparentedTimestamp": 1653686352,
  "Stats": {},
  "LastError": null
}

http://localhost:15000/api/tablet_statuses/?keyspace=all&cell=all&type=all&metric=lag

Before

[
  {
    "Data": [
      [
        0
      ]
    ],
    "Aliases": null,
    "KeyspaceLabel": {
      "Name": "commerce",
      "Rowspan": 1
    },
    "CellAndTypeLabels": [
      {
        "CellLabel": {
          "Name": "zone1",
          "Rowspan": 1
        },
        "TypeLabels": null
      }
    ],
    "ShardLabels": [
      "0"
    ],
    "YGridLines": [
      0.5
    ]
  }
]

After

[
  {
    "Data": [
      [
        0
      ]
    ],
    "Aliases": null,
    "KeyspaceLabel": {
      "Name": "commerce",
      "Rowspan": 1
    },
    "CellAndTypeLabels": [
      {
        "CellLabel": {
          "Name": "zone1",
          "Rowspan": 1
        },
        "TypeLabels": null
      }
    ],
    "ShardLabels": [
      "0"
    ],
    "YGridLines": [
      0.5
    ]
  }
]

[deepthi]

Nice work! Everything looks good except for a few minor comments.
We can merge once those are addressed.

[deepthi]

Not sure why this needs to change in this PR?

[frouioui]

We use the FakeHealthCheck in these tests. The implementation used to ignore the cell and use FakeCell always, this was changed, so now the output of the test uses the real cell's name.