fix(exporter-prometheus): add appendTimestamp option to ExporterConfig

[antoniomrfranco]

Which problem is this PR solving?

• PrometheusSerializer has a property called appendTimestamp. However, this property cannot be changed anywhere. This PR fixes this issue, which is also discussed in Question: best way to set PrometheusExporter._serializer._appendTimestamp = false #1695.

Short description of the changes

• This PR adds the appendTimestamp option to ExporterConfig. This option is used to control whether the timestamp will be included when exporting the metric or not. The default behavior was not changed, i.e., appendTimestamp defaults to true.

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Antônio Franco (835cd73)

[codecov]

Codecov Report

Merging #1697 (0749345) into master (e70a7c8) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1697   +/-   ##
=======================================
  Coverage   92.17%   92.17%           
=======================================
  Files         167      167           
  Lines        5594     5597    +3     
  Branches     1191     1193    +2     
=======================================
+ Hits         5156     5159    +3     
  Misses        438      438           

Impacted Files	Coverage Δ
...etry-exporter-prometheus/src/PrometheusExporter.ts	92.18% <100.00%> (+0.38%)	⬆️

[legendecas]

Welcome to the project :). LGTM.

[obecny]

lgtm, just last minor thing

[antoniomrfranco]

It seems that the lint check broke after I updated my branch merging master.

[dyladan]

Looks fine but why is this configurable in the first place? Shouldn't we always append the timestamp?

[antoniomrfranco]

Looks fine but why is this configurable in the first place? Shouldn't we always append the timestamp?

Hi @dyladan. I don't think we should always append the timestamp. Actually, in Prometheus docs, they say that

you should not set timestamps on the metrics you expose, let Prometheus take care of that. If you think you need timestamps, then you probably need the Pushgateway instead.

So I think that timestamp is only required when you have a Pushgateway or a federated architecture (e.g., Prometheus pushing metrics to Cortex).

[dyladan]

In that case, should we remove the timestamp option? Sounds like prometheus itself doesn't recommend its use.