nodejs_version_info empty after registry reset

[ssube]

I've been using this library in a small bot with great results, and recently implemented a feature where SIGINT and SIGHUP will reload the config file and reset any stateful counters (for development). I'm using collectDefaultMetrics({ registry }) to collect general Node metrics and call registry.resetMetrics upon receiving the signals.

After calling resetMetrics and waiting for the next interval tick, most metrics re-appear, but not all of them:

# HELP nodejs_heap_space_size_available_bytes Process heap space size available from node.js in bytes.
# TYPE nodejs_heap_space_size_available_bytes gauge
nodejs_heap_space_size_available_bytes{space="new"} 658168 1546562858531
nodejs_heap_space_size_available_bytes{space="old"} 1583448 1546562858531
nodejs_heap_space_size_available_bytes{space="code"} 456544 1546562858531
nodejs_heap_space_size_available_bytes{space="map"} 514160 1546562858531
nodejs_heap_space_size_available_bytes{space="large_object"} 1397517824 1546562858531

# HELP nodejs_version_info Node.js version info.
# TYPE nodejs_version_info gauge

It would make sense that nodejs_version_info is only collected once, as it is very unlikely to change, but it seems to get lost after the registry is reset.

What's the best way to make sure that metric is always populated? It would be pretty easy for me to clear the interval and call collectDefaultMetrics again, if that makes sense.

Edit: reading further, it looks like this may be a non-issue if #180 is implemented as discussed, since my code would call that each time rather than set and reset an interval. Would that be the most correct solution?

[siimon]

Yeah I would say that fixing it as suggested in #180 would be the way to fix this problem as well!

[sam-github]

@ssube was this fixed by #180?

[ssube]

Not quite - after resetting the registry, the nodejs_version_info gauge remains empty forever. The other metrics are being updated every sample, especially visible with memory.

I had to make a few other changes for v12.0 (ssube/isolex#837), but have gotten it working with a hard-coded (for the moment) timeout of 10 (https://github.com/ssube/isolex/pull/837/files#diff-5a28ddf4a6b3741f1800b6fcc801c9b1R42):

    this.collector({
      register: this.metrics,
      timeout: 10,
    });

Metrics:

# HELP nodejs_heap_space_size_available_bytes Process heap space size available from Node.js in bytes.
# TYPE nodejs_heap_space_size_available_bytes gauge
nodejs_heap_space_size_available_bytes{space="read_only"} 229576
nodejs_heap_space_size_available_bytes{space="new"} 415016
nodejs_heap_space_size_available_bytes{space="old"} 1980992
nodejs_heap_space_size_available_bytes{space="code"} 28416
nodejs_heap_space_size_available_bytes{space="map"} 1101440
nodejs_heap_space_size_available_bytes{space="large_object"} 0
nodejs_heap_space_size_available_bytes{space="code_large_object"} 0
nodejs_heap_space_size_available_bytes{space="new_large_object"} 1047488

# HELP nodejs_version_info Node.js version info.
# TYPE nodejs_version_info gauge

# HELP nodejs_gc_duration_seconds Garbage collection duration by kind, one of major, minor, incremental or weakcb.
# TYPE nodejs_gc_duration_seconds histogram
nodejs_gc_duration_seconds_bucket{le="0.001",kind="minor"} 7
nodejs_gc_duration_seconds_bucket{le="0.01",kind="minor"} 7
nodejs_gc_duration_seconds_bucket{le="0.1",kind="minor"} 7
nodejs_gc_duration_seconds_bucket{le="1",kind="minor"} 7
nodejs_gc_duration_seconds_bucket{le="2",kind="minor"} 7
nodejs_gc_duration_seconds_bucket{le="5",kind="minor"} 7
nodejs_gc_duration_seconds_bucket{le="+Inf",kind="minor"} 7
nodejs_gc_duration_seconds_sum{kind="minor"} 0.0019990769999999997
nodejs_gc_duration_seconds_count{kind="minor"} 7

Not sure if this is something I'm doing wrong or related to how the version info is being collected.

[sam-github]

Probably the version gauge needs to return a collect function. It didn't before, and doesn't now, because the values never change. I guess the interaction with reset wasn't considered.