How to explain that almost all programs use http.Handle("/metrics", promhttp.Handler())

[kaka LI]

I am going to set up monitoring by myself. I am a novice. I started two programs 8081 8082 in `examples/simple/main.go`. I found that they all bring a lot of built-in prometheus indicators. My question is:

1. How to explain why all programs need to start promhttp.Handler() to expose indicators? Is it a best practice?

2. There are too many indicators with the same name. Can the indicators exposed by various programs through promhttp.Handler() be aggregated? (Except summary)

Thank you everyone

8081

```shell

# curl localhost:8081/metrics

# HELP go_gc_duration_seconds A summary of the pause duration of garbage collection cycles.

# TYPE go_gc_duration_seconds summary

go_gc_duration_seconds{quantile="0"} 0

go_gc_duration_seconds{quantile="0.25"} 0

go_gc_duration_seconds{quantile="0.5"} 0

go_gc_duration_seconds{quantile="0.75"} 0

go_gc_duration_seconds{quantile="1"} 0

go_gc_duration_seconds_sum 0

go_gc_duration_seconds_count 0

# HELP go_goroutines Number of goroutines that currently exist.

# TYPE go_goroutines gauge

go_goroutines 8

# HELP go_info Information about the Go environment.

# TYPE go_info gauge

go_info{version="go1.16.2"} 1

# HELP go_memstats_alloc_bytes Number of bytes allocated and still in use.

# TYPE go_memstats_alloc_bytes gauge

go_memstats_alloc_bytes 1.76352e+06

# HELP go_memstats_alloc_bytes_total Total number of bytes allocated, even if freed.

# TYPE go_memstats_alloc_bytes_total counter

go_memstats_alloc_bytes_total 1.76352e+06

# HELP go_memstats_buck_hash_sys_bytes Number of bytes used by the profiling bucket hash table.

# TYPE go_memstats_buck_hash_sys_bytes gauge

go_memstats_buck_hash_sys_bytes 1.444345e+06

# HELP go_memstats_frees_total Total number of frees.

# TYPE go_memstats_frees_total counter

go_memstats_frees_total 690

# HELP go_memstats_gc_cpu_fraction The fraction of this program's available CPU time used by the GC since the program started.

# TYPE go_memstats_gc_cpu_fraction gauge

go_memstats_gc_cpu_fraction 0

# HELP go_memstats_gc_sys_bytes Number of bytes used for garbage collection system metadata.

# TYPE go_memstats_gc_sys_bytes gauge

go_memstats_gc_sys_bytes 4.104008e+06

# HELP go_memstats_heap_alloc_bytes Number of heap bytes allocated and still in use.

# TYPE go_memstats_heap_alloc_bytes gauge

go_memstats_heap_alloc_bytes 1.76352e+06

# HELP go_memstats_heap_idle_bytes Number of heap bytes waiting to be used.

# TYPE go_memstats_heap_idle_bytes gauge

go_memstats_heap_idle_bytes 6.3987712e+07

# HELP go_memstats_heap_inuse_bytes Number of heap bytes that are in use.

# TYPE go_memstats_heap_inuse_bytes gauge

go_memstats_heap_inuse_bytes 2.629632e+06

# HELP go_memstats_heap_objects Number of allocated objects.

# TYPE go_memstats_heap_objects gauge

go_memstats_heap_objects 5005

# HELP go_memstats_heap_released_bytes Number of heap bytes released to OS.

# TYPE go_memstats_heap_released_bytes gauge

go_memstats_heap_released_bytes 6.3987712e+07

# HELP go_memstats_heap_sys_bytes Number of heap bytes obtained from system.

# TYPE go_memstats_heap_sys_bytes gauge

go_memstats_heap_sys_bytes 6.6617344e+07

# HELP go_memstats_last_gc_time_seconds Number of seconds since 1970 of last garbage collection.

# TYPE go_memstats_last_gc_time_seconds gauge

go_memstats_last_gc_time_seconds 0

# HELP go_memstats_lookups_total Total number of pointer lookups.

# TYPE go_memstats_lookups_total counter

go_memstats_lookups_total 0

# HELP go_memstats_mallocs_total Total number of mallocs.

# TYPE go_memstats_mallocs_total counter

go_memstats_mallocs_total 5695

# HELP go_memstats_mcache_inuse_bytes Number of bytes in use by mcache structures.

# TYPE go_memstats_mcache_inuse_bytes gauge

go_memstats_mcache_inuse_bytes 67200

# HELP go_memstats_mcache_sys_bytes Number of bytes used for mcache structures obtained from system.

# TYPE go_memstats_mcache_sys_bytes gauge

go_memstats_mcache_sys_bytes 81920

# HELP go_memstats_mspan_inuse_bytes Number of bytes in use by mspan structures.

# TYPE go_memstats_mspan_inuse_bytes gauge

go_memstats_mspan_inuse_bytes 47872

# HELP go_memstats_mspan_sys_bytes Number of bytes used for mspan structures obtained from system.

# TYPE go_memstats_mspan_sys_bytes gauge

go_memstats_mspan_sys_bytes 49152

# HELP go_memstats_next_gc_bytes Number of heap bytes when next garbage collection will take place.

# TYPE go_memstats_next_gc_bytes gauge

go_memstats_next_gc_bytes 4.473924e+06

# HELP go_memstats_other_sys_bytes Number of bytes used for other system allocations.

# TYPE go_memstats_other_sys_bytes gauge

go_memstats_other_sys_bytes 1.088455e+06

# HELP go_memstats_stack_inuse_bytes Number of bytes in use by the stack allocator.

# TYPE go_memstats_stack_inuse_bytes gauge

go_memstats_stack_inuse_bytes 491520

# HELP go_memstats_stack_sys_bytes Number of bytes obtained from system for stack allocator.

# TYPE go_memstats_stack_sys_bytes gauge

go_memstats_stack_sys_bytes 491520

# HELP go_memstats_sys_bytes Number of bytes obtained from system.

# TYPE go_memstats_sys_bytes gauge

go_memstats_sys_bytes 7.3876744e+07

# HELP go_threads Number of OS threads created.

# TYPE go_threads gauge

go_threads 9

# HELP process_cpu_seconds_total Total user and system CPU time spent in seconds.

# TYPE process_cpu_seconds_total counter

process_cpu_seconds_total 0.02

# HELP process_max_fds Maximum number of open file descriptors.

# TYPE process_max_fds gauge

process_max_fds 1.048576e+06

# HELP process_open_fds Number of open file descriptors.

# TYPE process_open_fds gauge

process_open_fds 10

# HELP process_resident_memory_bytes Resident memory size in bytes.

# TYPE process_resident_memory_bytes gauge

process_resident_memory_bytes 1.4229504e+07

# HELP process_start_time_seconds Start time of the process since unix epoch in seconds.

# TYPE process_start_time_seconds gauge

process_start_time_seconds 1.63175799303e+09

# HELP process_virtual_memory_bytes Virtual memory size in bytes.

# TYPE process_virtual_memory_bytes gauge

process_virtual_memory_bytes 1.265545216e+09

# HELP process_virtual_memory_max_bytes Maximum amount of virtual memory available in bytes.

# TYPE process_virtual_memory_max_bytes gauge

process_virtual_memory_max_bytes 1.8446744073709552e+19

# HELP promhttp_metric_handler_requests_in_flight Current number of scrapes being served.

# TYPE promhttp_metric_handler_requests_in_flight gauge

promhttp_metric_handler_requests_in_flight 1

# HELP promhttp_metric_handler_requests_total Total number of scrapes by HTTP status code.

# TYPE promhttp_metric_handler_requests_total counter

promhttp_metric_handler_requests_total{code="200"} 2

promhttp_metric_handler_requests_total{code="500"} 0

promhttp_metric_handler_requests_total{code="503"} 0

```

8082

```shell

# curl localhost:8082/metrics

# HELP go_gc_duration_seconds A summary of the pause duration of garbage collection cycles.

# TYPE go_gc_duration_seconds summary

go_gc_duration_seconds{quantile="0"} 0

go_gc_duration_seconds{quantile="0.25"} 0

go_gc_duration_seconds{quantile="0.5"} 0

go_gc_duration_seconds{quantile="0.75"} 0

go_gc_duration_seconds{quantile="1"} 0

go_gc_duration_seconds_sum 0

go_gc_duration_seconds_count 0

# HELP go_goroutines Number of goroutines that currently exist.

# TYPE go_goroutines gauge

go_goroutines 7

# HELP go_info Information about the Go environment.

# TYPE go_info gauge

go_info{version="go1.16.2"} 1

# HELP go_memstats_alloc_bytes Number of bytes allocated and still in use.

# TYPE go_memstats_alloc_bytes gauge

go_memstats_alloc_bytes 3.04896e+06

# HELP go_memstats_alloc_bytes_total Total number of bytes allocated, even if freed.

# TYPE go_memstats_alloc_bytes_total counter

go_memstats_alloc_bytes_total 3.04896e+06

# HELP go_memstats_buck_hash_sys_bytes Number of bytes used by the profiling bucket hash table.

# TYPE go_memstats_buck_hash_sys_bytes gauge

go_memstats_buck_hash_sys_bytes 1.444561e+06

# HELP go_memstats_frees_total Total number of frees.

# TYPE go_memstats_frees_total counter

go_memstats_frees_total 2136

# HELP go_memstats_gc_cpu_fraction The fraction of this program's available CPU time used by the GC since the program started.

# TYPE go_memstats_gc_cpu_fraction gauge

go_memstats_gc_cpu_fraction 0

# HELP go_memstats_gc_sys_bytes Number of bytes used for garbage collection system metadata.

# TYPE go_memstats_gc_sys_bytes gauge

go_memstats_gc_sys_bytes 4.178024e+06

# HELP go_memstats_heap_alloc_bytes Number of heap bytes allocated and still in use.

# TYPE go_memstats_heap_alloc_bytes gauge

go_memstats_heap_alloc_bytes 3.04896e+06

# HELP go_memstats_heap_idle_bytes Number of heap bytes waiting to be used.

# TYPE go_memstats_heap_idle_bytes gauge

go_memstats_heap_idle_bytes 6.2644224e+07

# HELP go_memstats_heap_inuse_bytes Number of heap bytes that are in use.

# TYPE go_memstats_heap_inuse_bytes gauge

go_memstats_heap_inuse_bytes 3.940352e+06

# HELP go_memstats_heap_objects Number of allocated objects.

# TYPE go_memstats_heap_objects gauge

go_memstats_heap_objects 11423

# HELP go_memstats_heap_released_bytes Number of heap bytes released to OS.

# TYPE go_memstats_heap_released_bytes gauge

go_memstats_heap_released_bytes 6.2570496e+07

# HELP go_memstats_heap_sys_bytes Number of heap bytes obtained from system.

# TYPE go_memstats_heap_sys_bytes gauge

go_memstats_heap_sys_bytes 6.6584576e+07

# HELP go_memstats_last_gc_time_seconds Number of seconds since 1970 of last garbage collection.

# TYPE go_memstats_last_gc_time_seconds gauge

go_memstats_last_gc_time_seconds 0

# HELP go_memstats_lookups_total Total number of pointer lookups.

# TYPE go_memstats_lookups_total counter

go_memstats_lookups_total 0

# HELP go_memstats_mallocs_total Total number of mallocs.

# TYPE go_memstats_mallocs_total counter

go_memstats_mallocs_total 13559

# HELP go_memstats_mcache_inuse_bytes Number of bytes in use by mcache structures.

# TYPE go_memstats_mcache_inuse_bytes gauge

go_memstats_mcache_inuse_bytes 67200

# HELP go_memstats_mcache_sys_bytes Number of bytes used for mcache structures obtained from system.

# TYPE go_memstats_mcache_sys_bytes gauge

go_memstats_mcache_sys_bytes 81920

# HELP go_memstats_mspan_inuse_bytes Number of bytes in use by mspan structures.

# TYPE go_memstats_mspan_inuse_bytes gauge

go_memstats_mspan_inuse_bytes 65280

# HELP go_memstats_mspan_sys_bytes Number of bytes used for mspan structures obtained from system.

# TYPE go_memstats_mspan_sys_bytes gauge

go_memstats_mspan_sys_bytes 65536

# HELP go_memstats_next_gc_bytes Number of heap bytes when next garbage collection will take place.

# TYPE go_memstats_next_gc_bytes gauge

go_memstats_next_gc_bytes 4.473924e+06

# HELP go_memstats_other_sys_bytes Number of bytes used for other system allocations.

# TYPE go_memstats_other_sys_bytes gauge

go_memstats_other_sys_bytes 997839

# HELP go_memstats_stack_inuse_bytes Number of bytes in use by the stack allocator.

# TYPE go_memstats_stack_inuse_bytes gauge

go_memstats_stack_inuse_bytes 524288

# HELP go_memstats_stack_sys_bytes Number of bytes obtained from system for stack allocator.

# TYPE go_memstats_stack_sys_bytes gauge

go_memstats_stack_sys_bytes 524288

# HELP go_memstats_sys_bytes Number of bytes obtained from system.

# TYPE go_memstats_sys_bytes gauge

go_memstats_sys_bytes 7.3876744e+07

# HELP go_threads Number of OS threads created.

# TYPE go_threads gauge

go_threads 10

# HELP process_cpu_seconds_total Total user and system CPU time spent in seconds.

# TYPE process_cpu_seconds_total counter

process_cpu_seconds_total 0.07

# HELP process_max_fds Maximum number of open file descriptors.

# TYPE process_max_fds gauge

process_max_fds 1.048576e+06

# HELP process_open_fds Number of open file descriptors.

# TYPE process_open_fds gauge

process_open_fds 10

# HELP process_resident_memory_bytes Resident memory size in bytes.

# TYPE process_resident_memory_bytes gauge

process_resident_memory_bytes 1.5106048e+07

# HELP process_start_time_seconds Start time of the process since unix epoch in seconds.

# TYPE process_start_time_seconds gauge

process_start_time_seconds 1.63175811943e+09

# HELP process_virtual_memory_bytes Virtual memory size in bytes.

# TYPE process_virtual_memory_bytes gauge

process_virtual_memory_bytes 1.341308928e+09

# HELP process_virtual_memory_max_bytes Maximum amount of virtual memory available in bytes.

# TYPE process_virtual_memory_max_bytes gauge

process_virtual_memory_max_bytes 1.8446744073709552e+19

# HELP promhttp_metric_handler_requests_in_flight Current number of scrapes being served.

# TYPE promhttp_metric_handler_requests_in_flight gauge

promhttp_metric_handler_requests_in_flight 1

# HELP promhttp_metric_handler_requests_total Total number of scrapes by HTTP status code.

# TYPE promhttp_metric_handler_requests_total counter

promhttp_metric_handler_requests_total{code="200"} 7

promhttp_metric_handler_requests_total{code="500"} 0

promhttp_metric_handler_requests_total{code="503"} 0

```

[Stuart Clark]

> 2. There are too many indicators with the same name. Can the
> indicators exposed by various programs through promhttp.Handler() be
> aggregated? (Except summary)
>

What do you mean by "too many indicators with the same name"?

The client libraries expose a number of metrics around the application,
allowing you basic visibility without writing any code. Each metric is
different, with labels used to split things as needed (e.g. for
histograms).

What is the issue you are seeing?

--
Stuart Clark

[kazakaze]

thank you for your reply.

E.g. promhttp_metric_handler_requests_total,   promhttp_metric_handler_requests_in_flight , process_virtual_memory_bytes  

Different programs have their basic visibility. Can indicators with the same name of different programs be aggregated and displayed?

[Stuart Clark]

On 2021-09-16 11:59, kazakaze wrote:
> thank you for your reply.
>
> E.g. promhttp_metric_handler_requests_total,
> promhttp_metric_handler_requests_in_flight ,
> process_virtual_memory_bytes
>

> Different programs have their basic visibility. Can INDICATORS WITH
> THE SAME NAME OF DIFFERENT PROGRAMS be aggregated and displayed?

OK. Yep you can aggregate things together when you are running queries
on the data stored within Prometheus (making sure that whatever you are
summing/counting/min/max, etc. makes sense).

For example with the metrics listed above I could see some use in
aggregating the virtual memory usage for things running on the same box,
but the other two don't sound that useful to aggregate.

--
Stuart Clark

[Bjoern Rabenstein]

On 15.09.21 19:45, kaka LI wrote:
> 1. How to explain why all programs need to start promhttp.Handler() to
> expose indicators? Is it a best practice?

It's not just best practice, it is _the_ way how Prometheus collects
metrics: The Prometheus server scrapes the monitored targets via
HTTP, so all targets that want to be monitored have to serve HTTP
somehow. In Go, programs will usually use the Go net/http package for
that, and that package defines the http.Handler type etc.

In other languages, you use whatever tools are available to serve
HTTP. In many cases, the monitored targets already serve HTTP as part
of their production work load. In that case, you can either expose the
metrics via a separate path (`/metrics` is indeed just a convention,
any path will do), or you open a separate HTTP socket.

--
Björn Rabenstein
[PGP-ID] 0x851C3DA17D748D03
[email] bjo...@rabenste.in

[kazakaze]

Thank you for your explanation of question 1.

[kazakaze]

Thank you for your explanation of question 2, I will put it into practice.