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Migrating applications from MicroProfile Metrics 1.x to MicroProfile Metrics 2.0

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David Chan and Charlotte Holt on Jul 24, 2019

MicroProfile Metrics 2.0 introduces several changes that must be considered when you migrate applications from MicroProfile Metrics 1.x. These changes include both architectural and API changes.

Counter and Concurrent Gauge

In MicroProfile Metrics 1.x, the behavior of the counter metric was either monotonic or non-monotonic. A monotonic counter was only able to count incrementally, whereas a non-monotonic counter was able to be both incremented and decremented. In MicroProfile Metrics 2.x, this dual behavior is separated. A counter in MicroProfile Metrics 2.x is inherently monotonic, and a new type of metric, called a concurrent gauge, is introduced with this release. The concurrent gauge metric exhibits the behavior of what was formerly the non-monotonic counter. Neither the counter metric nor the concurrent gauge metric has the monotonic parameter.

The following example shows how a counter metric is used in MicroProfile Metrics 1.x:

@Counted(name=countConcurrent") // monotonic = false by default
void somethingToCountInParallel() {
    // method logic here...
}

@Counted(name=“countSequential“, monotonic=true)
void somethingToCount() {
    // method logic here...
}

The following example shows how a counter metric is used in MicroProfile Metrics 2.x:

@ConcurrentGauge(name=countConcurrent ")
void somethingToCountInParallel() {
    // method logic here...
}

@Counted(name=“countSequential“)
void somethingToCount() {
    // method logic here...
}

Metadata

With MicroProfile Metrics 2.x, the Metadata object cannot be directly constructed. It can be created only with the use of a MetadataBuilder object, and the Metadata object that is constructed is immutable. Additionally, tag values are no longer associated with Metadata objects.

The following example shows how a Metadata object is constructed in MicroProfile Metrics 1.x:

Metadata servletCounterMetadata = new Metadata("servletCounter", "Servlet Counter Display Name", "This is a description", MetricType.Counter, MetricUnits.NONE, "tagKey=tagValue");
servletCounterMetadata.setName("newName");

The following example shows how a Metadata object is constructed in MicroProfile Metrics 2.x:

Metadata servletCounterMetadata = Metadata.builder().withName("servletCounter").withDisplayName("Servlet Counter Display Name").withDescription("This is a description").withType(MetricType.Counter).withUnits(MetricUnits.NONE).build();

Tags and MetricRegistry

The metric tags are no longer associated with Metadata objects. With MicroProfile Metrics 2.x, tags are independent entities within the MetricRegistry. This change comes along with the introduction of multi-dimensional metrics. In Microprofile Metrics 1.x, each metric must use a unique name. In MicroProfile Metrics 2.x, there can be multiple metrics with the same name and of the same type if the metrics have a different set of tags. The Java API introduced a Tag object that must be created and passed into the MetricRegistry when you register a metric programmatically.

The following example shows how a Tag object is constructed and used in MicroProfile Metrics 2.x:

Tag firstTag = new Tag("TagOneName", "TagOneValue");
Tag secondTag = new Tag("TagTwoName", "TagTwoValue");
metricRegistry.counter(servletCounterMetadata, firstTag, secondTag);

JSON output

In MicroProfile Metrics 2.x, the JSON-formatted output of metrics is modified to accommodate the changes introduced with the multi-dimensional tags. Because multiple metrics can now use the same name, the JSON-formatted data retrieved from both the GET and OPTIONS requests is modified.

For the endpoint to return JSON-formatted data, the Accept header of the request must include the application/json value.

When you start a GET request, tag values are appended to the metric name as ";<tagName>=<tagValue>". When you start an OPTIONS request, tags are listed as a nested list of <key>=<value> string values.

The following examples show how the metrics from GET and OPTIONS requests are formatted when using MicroProfile Metrics 1.x:

GET request:

{
  "shapeCounter"
}

OPTIONS request:

{
  shapeCounter": {
    "unit": “none",
    "type": counter",
    "description": “Counts shapes”
    "displayName": “shape counter”
    “tags”: "color=red,shape=triangle",
  }
}

The following examples show how the metrics from GET and OPTIONS requests are formatted when using MicroProfile Metrics 2.x:

GET request:

{
  "shapeCounter;color=red;shape=triangle",
  "shapeCounter;color=blue;shape=square"
}

OPTIONS request:

{
  shapeCounter": {
    "unit": “none",
    "type": counter",
    "description": “Counts shapes”
    "displayName": “shape counter”
    “tags”: [
      [
        “color=red”,
        "shape=triangle"
      ]
      [
        “color=blue”,
        "shape=square"
      ]
    ]
  }
}

To review a detailed list of updates that are included in MicroProfile Metrics 2.x, see the MicroProfile Metrics specification.

If you want to learn more about how to build metrics into your code, check out Microservice observability with metrics.

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