step9

Demo Flow - Step 9

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Expose operational values

There is an option to expose operational values publicly.

Import the expvar package

import _ "expvar"

Restart the demo server and browse to http://localhost:8000/debug/vars.

Add custom exposed variable

Adding custom operational values is quite easy.

1. Import the expvar package, not anonymously
2. Define variables for the operational values
3. Add the custom variables to the exposed values

In this demo we will monitor the following information:

• Number of concurrent requests
• Total number of requests
• Total bytes read

Define the exposed variables:

var concurrentRequests expvar.Int
var totalRequests expvar.Int
var totalBytes expvar.Int

Publish a map variable with the metrics values:

metrics := expvar.NewMap("metrics")
metrics.Set("concurrentRequests", &concurrentRequests)
metrics.Set("totalRequests", &totalRequests)
metrics.Set("totalBytes", &totalBytes)

On every request, add to request metrics counters:

totalRequests.Add(1)
concurrentRequests.Add(1)
defer concurrentRequests.Add(-1)

Every time bytes are read - count the bytee

totalBytes.Add(int64(n))

(see modified source code in server.go)

Run the demo server again, run the benchmark and refresh the /debug/vars page - the custom operational information is available.

And we're done!