[#1262] Add Graylog input plugin

[alimousazy]

Required for all PRs:

• CHANGELOG.md updated
• Sign CLA (if not already signed)
• README.md updated (if adding a new plugin)

[sparrc]

Why allow users to set these headers? Content-Type and Accept should ALWAYS be application/json. Authorization should be controlled by providing an "auth_key" argument to users, which the plugin would then internally create the Authorization header for the user.

[alimousazy]

Done

[alimousazy]

All comments done, Please verify @sparrc

[sparrc]

don't make inputs.graylog.auth_key a map, just use two arguments username and password directly in the plugin

[sparrc]

@alimousazy Looks much better, thanks for the revisions, but there is one general change that I think still needs to happen. Since graylog appears to be returning a specific JSON format, like:

{
        "full_name": "org.graylog2.shared.journal.KafkaJournal.writeTime",
        "metric": {
          "time": {
            "min": 99
          },
          "rate": {
            "total": 10,
            "mean": 2
          },
          "duration_unit": "microseconds",
          "rate_unit": "events/second"
        },
        "name": "writeTime",
        "type": "hdrtimer"
      }

It seems like you should marshal the response JSON onto an object that looks something like this:

type ResponseMetrics struct {
  total   int
  Metrics []map[string]metric `json:"metrics"`
}

type metric struct {
  FullName string `json:"full_name"`
  name string
  type string
  metric map[string]interface{}
}

then you can make metric.FullName the telegraf metric name. Flatten metric.metric and make those the fields, and set metric.name and metric.type as tags.

[sparrc]

don't rename this import, use the built-in name

[alimousazy]

@sparrc Done
1- Writing comments about metrics.
2- Replace auth key with username and password.
3- Write Specific parser for Graylog metrics and change the structure

[sparrc]

remove TagKeys from the code since they're not used anymore

[alimousazy]

@sparrc

• Change the comment (less than 80 char) done.
• Tag Key removed.
• Added support for Namespace end point (Grouping for metrics) if User doesn't want to provide list of metrics to pull.

[sparrc]

Name doesn't appear to be getting used anymore, can you also remove it?

[sparrc]

Looking good @alimousazy, only other thing is Graylog.Name doesn't appear to be used anymore

[alimousazy]

Done removing name @sparrc