# Stackdriver Monitoring And Ruby

> Last updated: 2017-05-11

This week I have been learning how to access Stackdriver Monitoring with the [google-cloud-monitoring](https://github.com/GoogleCloudPlatform/google-cloud-ruby/tree/master/google-cloud-monitoring) gem. While Stackdriver Monitoring is a fully released product, the Ruby client library for monitoring is still at alpha level quality. I cannot in good conscience recommend that you use an alpha quality library for something as critical as monitoring. However, I know that some of you will do it anyway, so here are some tips for getting started.

## Installation and Authentication

You install the gem, unsurprisingly, with `gem install google-cloud-monitoring`. The monitoring gem depends on `grpc` which requires C extensions. There are some [open issues](https://github.com/grpc/grpc/labels/ruby) with installing this gem on some versions of Linux and with JRuby.

For the examples below I am authenticating via the credentials I set up with the `gcloud` SDK. There are several other methods of authenticating. The official documentation on authentication is [here](https://googlecloudplatform.github.io/google-cloud-ruby/#/docs/google-cloud/master/guides/authentication). My [blog post on authentication](http://www.thagomizer.com/blog/2017/01/11/authenticating-google-cloud-ruby-gems.html) goes into more detail on the how and why of the different authentication methods.

There’s some boilerplate setup you will need to do at the beginning of any script where you use the monitoring library.

```
require "google/cloud/monitoring/v3/metric_service_client"

client = Google::Cloud::Monitoring::V3::MetricServiceClient.new
project = Google::Cloud::Monitoring::V3::MetricServiceClient.project_path(PROJECT_ID)
```

The line that sets the project variable just ensures that the project is formatted in the way the monitoring API expects.

## Reading Metrics

Stackdriver Monitoring calls metric data a Time Series. To read metric data via the Ruby gem, you use the `MetricServiceClient#list_time_series` method. This method has four required parameters: name, filter, interval, and view.

Name is the formatted project name that I show in the boilerplate above. The view specifies which data should be returned. There are two possible values: `FULL` and `HEADERS`. Since I want the actual data, I am using `TimeSeriesView::FULL`. The filter parameter allows you to control what data is returned. There are many [supported filters](https://cloud.google.com/monitoring/api/v3/filters) including project, group, and resource type. For this post, I am going to look at the memory usage of the App Engine cluster running [“Tind-Purr”](http://www.thagomizer.com/blog/2017/03/09/rails-on-app-engine.html). You can look up the possible metrics with [metrics explorer](https://app.google.stackdriver.com/metrics-explorer). Using metric explorer, I figured out that the metric I want to see is “appengine/system/memory/usage”. When using this metric with the monitoring API, I need to specify the full name of the metric by adding `.googleapis.com` to it giving me “appengine.googleapis.com/system/memory/usage”.

The last parameter is the time interval. Specifying the interval is a bit of a challenge. You need to know the start and end time in seconds since the Unix epoch. In Ruby the fastest way to get this is calling `to_i` on a time object. The code below creates an end time that is the current timestamp and a start time that is 10 minutes before the end time.

```
end_time = Time.now.to_i
start_time = end_time - (60 * 10) # 10 minutes
```

Once I have the start and end time, I create a new TimeInterval object and then create a `Google::Protobuf::Timestamp` object for the start and end time.

```
interval = Google::Monitoring::V3::TimeInterval.new
interval.start_time = Google::Protobuf::Timestamp.new(seconds: start_time)
interval.end_time = Google::Protobuf::Timestamp.new(seconds: end_time)
```

Putting it all together, I get this code to read a metric time series.

```
require "google/cloud/monitoring/v3/metric_service_client"

client = Google::Cloud::Monitoring::V3::MetricServiceClient.new
project = Google::Cloud::Monitoring::V3::MetricServiceClient.project_path(PROJECT_ID)

metric = "appengine.googleapis.com/system/memory/usage"

end_time = Time.now.to_i
start_time = end_time - (60 * 10) # 10 minutes

filter = "metric.type = \"#{metric}\""
interval = Google::Monitoring::V3::TimeInterval.new
interval.start_time = Google::Protobuf::Timestamp.new(seconds: start_time)
interval.end_time = Google::Protobuf::Timestamp.new(seconds: end_time)
view = Google::Monitoring::V3::ListTimeSeriesRequest::TimeSeriesView::FULL

time_series = client.list_time_series(project, filter, interval, view)
```

This call returns a [`Google::Monitoring::V3::TimeSeries`](https://googlecloudplatform.github.io/google-cloud-ruby/#/docs/google-cloud-monitoring/v0.24.0/google/monitoring/v3/timeseries) object. This object has some metadata and an array of points. Each point is an instance of [`Google::Monitoring::V3::Point`](https://googlecloudplatform.github.io/google-cloud-ruby/#/docs/google-cloud-monitoring/v0.24.0/google/monitoring/v3/point) which has time information and a value object. To extract the value you need to know the type and call the appropriate method. The following code creates an array of all the integer values for a time series.

```
points = time_series.first.points.map { |p| p.value.int64_value }
```

This is the code you need to read a metric from Stackdriver Monitoring. In a future blog post, I will show you how to write a custom metrics to Stackdriver Monitoring from Ruby.

Please enable JavaScript to view the [comments powered by Disqus.](https://disqus.com/?ref_noscript)

 ![Aja Hammerly](/img/traditionalheadshot.jpg)

Aja Hammerly

Seattle, WA

### library\_books Series Index 

- [Developer Relations](/series#developer-relations)4
- [Machine Learning Basics](/series#machine-learning-basics)3
- [Battleship](/series#battleship)5
- [Talks I Love](/series#talks-i-love)6
- [Algorithms with Auntie Aja](/series#algorithms-with-auntie-aja)3
- [Ruby and GCP](/series#ruby-and-gcp)5
- [Playing with Data](/series#playing-with-data)3
- [Kubernetes & Rails](/series#kubernetes-rails)3
- [Learn To Code Resources](/series#learn-to-code-resources)3
- [Testing Anti-Patterns](/series#testing-anti-patterns)5