Support multi-target

[mateusduboli]

Adds support for multi-target pattern. Refers to #130

Discussion points:

• Should we always enable the scrapper by default? Is this possibly a security problem?

[mateusduboli]

@grobie

[mateusduboli]

@roidelapluie can you help us with this PR?

[grobie]

Apologies for the radio silence @mateusduboli.

@SuperQ @roidelapluie So I see that the project's stance on multi-targets has changed? I found @SuperQ's comment from February suggesting exactly this change https://github.com/prometheus/memcached_exporter/issues/111#issuecomment-1026606633.

The change looks good to me in general. I believe users should explicitly opt-in into the new behavior though by setting a flag. It might be unexpected and even harmful for users upgrading to the newest version if the exporter can be suddenly used to make requests against arbitrary endpoints.

[SuperQ]

Yes, we've been adding multi-target exporter scrape support across the ecosystem to better support hosted/blackbox managed instances like Elasticache.

[SuperQ]

I don't think we've added any blockers / flags to any other exporter that disable multi-target by default. We typically recommend users that care implement auth/tls.

[mateusduboli]

Hi @grobie and @SuperQ, anything else that we can do to get this merged?

[mateusduboli]

@SuperQ @maxbrunet Any updates here?

[mateusduboli]

@SuperQ done ✅

[pplu]

Can this get merged and released? It is a super-useful feature, and it looks like everything that was asked for has been done.

[mateusduboli]

@SuperQ @grobie any updates?

[chewrocca]

This feature seems helpful, but it has been open for several months without recent activity or approval. Is there a specific reason for the delay? Could someone help resolve any conflicts and get this merged?

[matthiasr]

We wrapped this up in #173.

[SuperQ]

Completed in https://github.com/prometheus/memcached_exporter/pull/173

[matthiasr]

Thank you for your contribution!