Expose Prometheus metrics in Perl programs

SLI And SLO

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SLI( Service quality indicators )  It refers to a specific quantitative indicator of the quality of a service ( If the request is delayed 、 Error rate 、QPS).

SLO( Service quality objectives ) Is a service SLI The target value , for example , We can define one SLO, requirement 95% The delay of the request of is less than 100ms.

SLI And SLO It is the transformation of traditional operation and maintenance SRE A topic that cannot be bypassed , They are SRE The core of practice . Traditional operation and maintenance usually pursues 100% The usability of , But this goal is impossible , By implementing SLO, It can bring the following benefits ：

• Monitor application behavior , In order to better improve the application

• Prioritize your work , That is, developing new features or ensuring service stability

• Use as a means of control , By comparison SLI And SLO, Decide whether to perform an operation

• Establish user expectations

Definition SLI

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To implement SLO, First, define SLI, and Prometheus Monitoring is the definition SLI A good tool for , The following will be introduced in Perl Exposed in the program Prometheus Metric To define SLI.

stay Perl Exposed in the program Prometheus Metric

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stay Perl Exposed in the program Prometheus Metric, We use two modules ：

• Dancer2 [1]：Perl It's a lightweight Web Application framework .

• Net::Prometheus [2]: Perl Of Prometheus  Client library

With the help of these two modules , We are Perl Statistics in the application '/login'  Number of calls to the interface ：

#!/usr/bin/perl

use strict;
use warnings;
use Dancer2;
use Net::Prometheus;
#  Use  Time::HiRes  Module  time  Function to get milliseconds  Epoch  Time 
use Time::HiRes qw/time/;

set host => '0.0.0.0';
set port => 3678;

#  initialization  Prometheus  client 
my $client = Net::Prometheus->new;
#  Set up  counter  Type of  metric, And designate  metric  Of  name, help, labels  Information 
my $counter = $client->new_counter(
    name => "requests_count",
    help => "Number of received requests",
    labels => ['path']
);

 post '/login' => sub {
    # counter  Add 1, Set up  label  by  path=login
    # $counter->inc({path => 'login'});  or 
    $counter->inc(('login'));
    # do something else
};

get '/metrics' => sub {
    if(request->user_agent =~ /curl|prometheus/i) {
        $client->render
    } else {
        "<pre>" . $client->render . "</pre>"
    }   
};

Run the top Perl Program , And open the browser , Enter the address ：

http://SERVER-IP:3678/metrics

among ,SERVER-IP by Perl The server where the program is located IP.

After the browser opens the above address , You can see the output of Prometheus metrics 了 ：

# HELP perl_heap_arenas Number of arenas in the Perl heap
# TYPE perl_heap_arenas gauge
perl_heap_arenas 713
# HELP perl_heap_svs Number of SVs in the Perl heap
# TYPE perl_heap_svs gauge
perl_heap_svs 120441
...
# HELP requests_count Number of received requests
# TYPE requests_count counter

however , We don't see what we define requests_count indicators , I only see the annotation information of this indicator ：

# HELP requests_count Number of received requests
# TYPE requests_count counter

This is because '/login'  This interface has not been accessed , Try to visit '/login'  After this interface , Refresh the browser and check again Prometheus Metrics You can see the indicators we defined ：

# HELP requests_count Number of received requests
# TYPE requests_count counter
requests_count{path="login"} 1

Come here , We have been successful for our Perl The application is exposed Prometheus Metrics.

With Counter Indicators of type requests_count, We can use Prometheus Of rate() function [3]  To calculate access '/login' Interface QPS, So we have a definition of SLI.

Net::Prometheus In addition to supporting counter Type of metric, And support gauge,summary,histogram Type of metric, The methods of use are similar , For detailed instructions, please refer to Net::Prometheus Documents [2].

Reference resources

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[1]: https://metacpan.org/pod/Dancer2

[2]: https://metacpan.org/pod/Net::Prometheus

[3]: https://prometheus.io/docs/prometheus/latest/querying/functions/#rate

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