Support env overrides for all inputs of the same type

[gunnaraasen]

Required for all non-trivial PRs

• Rebased/mergable
• Tests pass
• CHANGELOG.md updated
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Allows a default environment variable override to be specified for all config config sections that are arrays. This keeps backward compatibility for existing environment variable overrides on sections which now allow multiple services to be configured due to #6228 and #6333.

Given the following configuration for just the Graphite sections:

[[graphite]]
  enabled = true
  bind-address = ":2003"

[[graphite]]
  enabled = true
  bind-address = ":8085"

And setting the following environment variables:

# Override all Graphite input's bind address setting to :1003 
INFLUXDB_GRAPHITE_BIND_ADDRESS=:1003
# Override the second Graphite input's bind address setting to :3003
INFLUXDB_GRAPHITE_1_BIND_ADDRESS=:3003

The current code will result in the first Graphite input using bind address :2003 and the second Graphite input using a bind address of :3003.

This PR results in the first Graphite input using bind address :1003 and the second Graphite input using a bind address of :3003.

[jsternberg]

So I'm clear on what this does, what does the current version allow and what are you trying to change?

I only see the ability to specify one http section in the config at the moment so I'm not sure how the example in the explanation would work. For the unit test, I see it trying to set the zeroth UDP bind address, but it definitely seems like 0 should refer to the first index in the slice, not the second.

[jsternberg]

This code specifically seems to be wrong. This code is confusing so I'm not certain, but I think this would allow me to say INFLUXDB_0_BIND_ADDRESS to set all of the bind addresses in every section where that applies. If I'm reading this right, the unit test you have should work with the original code.

[gunnaraasen]

The unit test doesn't work with the current code because inputs which allow multiple listeners don't get matched to environment variables like INFLUXDB_UDP_BIND_ADDRESS, only INFLUXDB_UDP_[i]_BIND_ADDRESS. This change allows both to be used to override the bind address for a section and only applies to sections which allow multiple instances, which are all input sections (UDP, graphite, etc).

Not sure how this would match a INFLUXDB_0_BIND_ADDRESS env var to all bind addresses. Maybe I'm missing something.

[jsternberg]

Ah, I think I misunderstood the f.Index(i) code. I thought that was an integer index that got returned.

[gunnaraasen]

I opened #6333 to add support for multiple HTTP listeners but the example was poorly written. I've updated it to use a Graphite input and added a before and after description. Hope that helps clear up the confusing parts.

[e-dard]

LGTM 👍

[jsternberg]

👍