ifName agent default value

[Hipska]

Feature Request

Opening a feature request kicks off a discussion.
As discussed in #7763 (comment)

Proposal:

Let the default value of these be the same:

• agent for processors.ifname
• agent_host for inputs.snmp
• agent_address for inputs.sflow

Current behavior:

The default value (agent) mostly never useful.

Desired behavior:

The default value should be a logical one that makes sense or most users would not need to change.

Tasks

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1. feat(inputs.snmp): Hint to use source tag #14111
   area/snmp feat plugin/input ready for final review +4
   
2. feat(inputs.sflow): Add default source tag #14112
   area/network feat plugin/input +3
   
3. docs(processors.ifname): Document better agent tag name #14117
   area/snmp docs plugin/processor ready for final review +4
   
4. feat(processors.ifname): Deprecate plugin #14899
   feat plugin/processor waiting for response +3
   

[Hipska]

@reimda what do you think?

[Hipska]

Ping @ssoroka @reimda

[reimda]

I agree that the tags across these three plugins should match. It was an oversight from the beginning that they don't match.

We haven't been able to change the default because it will break anyone who is using the default. We can change the default on a major release (2.0) because major releases won't guarantee settings compatibility.

For now we ought to prepare for a change in 2.0 by choosing the tag we want to use across all three plugins and deprecating the defaults in all three plugins that don't match the tag we chose.

[Hipska]

According to #4413, source would be the most logical default value.

[srebhan]

@Hipska I think the source tag is already taken e.g. in inputs.snmp. Maybe we should add an additional agent tag for the inputs so you can tag_exclude the old one if you wish but downstream queries still work!?

[Hipska]

No, not by default. Only if you added a OID as tag and gave it that name.

[srebhan]

To which of they points is your comment? ;-)

[Hipska]

The first one, inputs.snmp does not have a source tag, it is using agent_host as explained in my initial post.

[powersj]

next steps: look at adding the source tag to the above three plugins in addition to the existing tags. Then determine if/when what minor release we could remove the old ones with documentation as to how to use the old tag name (e.g. processor) if users wanted to.

[Hipska]

@powersj I'm not sure how to deprecate the agent tag default value for the ifname processor. Did the other 2 already..