Don't pass metrics around

[nckturner]

• Remove need to pass metrics object around, but:
• Still allow a Registerer to be passed in avoids duplicate metrics
  registration errors during unit testing.

Testing by hitting metrics endpoint:

$ curl --cacert _output/dev/authenticator/state/cert.pem https://localhost:21362/metrics | grep aws_iam_authenticator
% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current                                                                                                              
                                 Dload  Upload   Total   Spent    Left  Speed                                                                                                                
100  7784    0  7784    0     # HELP aws_iam_authenticator_authenticate_latency_seconds Authenticate call latency                                                                            
0  # TYPE aws_iam_authenticator_authenticate_latency_seconds histogram                                                                                                                       
19aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="0.005"} 2                                                                                                   
00aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="0.01"} 2                                                                                                    
kaws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="0.025"} 3                                                                                                    
  aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="0.05"} 4                                                                                                    
  aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="0.1"} 4                                                                                                     
  aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="0.25"} 4                                                                                                    
0aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="0.5"} 4                                                                                                      
 -aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="1"} 4                                                                                                       
-:aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="2.5"} 4                                                                                                     
-aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="5"} 4                                                                                                        
-aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="10"} 4                                                                                                       
:aws_iam_authenticator_authenticate_latency_seconds_bucket{result="success",le="+Inf"} 4                                                                                                     
--aws_iam_authenticator_authenticate_latency_seconds_sum{result="success"} 0.061571109                                                                                                       
 -aws_iam_authenticator_authenticate_latency_seconds_count{result="success"} 4                                                                                                               
-:# HELP aws_iam_authenticator_configmap_watch_failures EKS Configmap watch failures                                                                                                         
--# TYPE aws_iam_authenticator_configmap_watch_failures counter                                                                                                                              
:-aws_iam_authenticator_configmap_watch_failures 0                                                                                                                                           
- --:--:-- 1900k      

[nckturner]

/retest

[jyotimahapatra]

could we try using an init function to avoid calling InitMetrics at all? Test and prod code will benefit from not having to call InitMetrics. Let me know how that looks.
Also if we did that, we could also try getting rid of the metrics struct and make ConfigMapWatchFailures and Latency top level vars. It's optional, but would like to know your thoughts

[nckturner]

The reason I call InitMetrics() explicitly is because we check metric counts in a many of our unit tests using this function, so we need a way to clear the metrics after each test run. Otherwise, we will need to refactor the tests to call prometheus.Unregister() in every test (we can use a TestMain here with setup and teardown functions to avoid explicit calls for each test). Do you prefer that approach?

[nckturner]

I stumbled across another approach of sampling the metric before and after the test is run and verifying the ending value is what is expected.

[jyotimahapatra]

so we need a way to clear the metrics after each test run

How do we clean up today?

[nckturner]

We don't need to because we create a new metrics namespace for each test setup.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jyotimahapatra, nckturner

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[jyotimahapatra]

/lgtm

[k8s-ci-robot]

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/lgtm

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[wongma7]

/lgtm