Add MosApiMetrics exporter

[njshah301]

Introduces the metrics exporter for the MoSAPI system.

• Implements MosApiMetrics to export TLD and service states to Cloud Monitoring.
• Maps ICANN MoSAPI status codes to numeric gauges: 1 (UP), 0 (DOWN), and 2 (DISABLED/INCONCLUSIVE).
• Sets MAX_TIMESERIES_PER_REQUEST to respect Cloud Monitoring API limits

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This change is 

[gbrodman]

@gbrodman reviewed 4 files and all commit messages, and made 18 comments.
Reviewable status: 4 of 6 files reviewed, 18 unresolved discussions (waiting on @CydeWeys, @njshah301, @ptkach, and @weiminyu).

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 103 at r1 (raw file):

    // Initialize Metric Descriptors once on startup
    ensureMetricDescriptors();

Don't do work in the constructor. It's bad practice, as it can lead to unexpected oddities.

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 146 at r1 (raw file):

          } catch (Exception e) {
            logger.atWarning().withCause(e).log(
                "Failed to create metric descriptors (they may already exist).");

if this is expected to happen regularly, it probably shouldn't be in an exception / warning case

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 156 at r1 (raw file):

      String displayName,
      String description,
      String metricKind,

this is always GAUGE right?

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 161 at r1 (raw file):

      throws IOException {

    List<LabelDescriptor> labelDescriptors = new ArrayList<>();

Use stream-collect (toImmutableList()) instead of manually constructing these

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 190 at r1 (raw file):

          try {
            pushBatchMetrics(states);
          } catch (Throwable t) {

Generally, avoid catching a raw Throwable. It can hide things. We should be more precise.

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 196 at r1 (raw file):

  }

  private void pushBatchMetrics(List<TldServiceState> states) throws IOException {

One batch failure shouldn't cause all the others to fail with an IOException. Catch the exception where it occurs, log it, and then try the next batch.

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 197 at r1 (raw file):

  private void pushBatchMetrics(List<TldServiceState> states) throws IOException {
    List<TimeSeries> allTimeSeries = new ArrayList<>();

Constructing a list piece by piece over many methods is brittle and it's not immediately clear where everything happens. Instead, convert the stream of TldServiceState into a stream of TimeSeries using flatMap (flatMap instead of just map because it seems like one TldServiceState maps to multiple TimeSeries objects)

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 199 at r1 (raw file):

    List<TimeSeries> allTimeSeries = new ArrayList<>();
    TimeInterval interval =
        new TimeInterval().setEndTime(new DateTime(System.currentTimeMillis()).toString());

Inject a clock and use that for the time instead of calling System

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 206 at r1 (raw file):

      // 2. Service-level Metrics
      Map<String, ServiceStatus> services = state.serviceStatuses();

state::serviceStatuses should use an immutable map if it doesn't already

can this ever even be null? if not, don't worry about the null case.

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 227 at r1 (raw file):

  private void addServiceMetrics(
      List<TimeSeries> list,

Use the full type (ImmutableList, ImmutableMap etc) whenever possible for clarity (this goes for elsewhere in the file, too)

If we ever specify the standard List/Map type it's usually because we're forced to by an API we don't control

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 254 at r1 (raw file):

      String suffix, Map<String, String> labels, Number val, TimeInterval interval) {
    Metric metric = new Metric().setType(METRIC_DOMAIN + suffix).setLabels(labels);
    MonitoredResource resource =

i don't think we need to recreate this object every time

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core/src/main/java/google/registry/mosapi/MosApiMetrics.java line 304 at r1 (raw file):

   */
  private long parseServiceStatus(String status) {
    if (status == null) {

By the time we've reached this point in the code, we should be guaranteed that the status has a non-null value. If the status is null, that means (as far as I'm aware) that the response from MosAPI was bad / wrong in a major way. If that happens, we should be taking care of that error when it happens, not here down the line.

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core/src/main/java/google/registry/config/files/default-config.yaml line 651 at r1 (raw file):

  # Metrics Reporting Thread Count
  # Set to 1. Given the current TLD volume and the 5-minute reporting interval,

better phrasing "Defaults to 1".

The rest of this should be phrased in a way that it can apply broadly to any user of Nomulus, not just us. Give guidance on how other people should properly set this field.

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core/src/main/java/google/registry/config/RegistryConfigSettings.java line 276 at r1 (raw file):

    public List<String> services;
    public int tldThreadCnt;

no extra line

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core/src/main/java/google/registry/mosapi/module/MosApiModule.java line 208 at r1 (raw file):

  /**
   * Provides a single-threaded executor for sequential metrics reporting.

This is a config point, so it's not necessary single-threaded.

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core/src/main/java/google/registry/mosapi/module/MosApiModule.java line 210 at r1 (raw file):

   * Provides a single-threaded executor for sequential metrics reporting.
   *
   * <p>Bound to 1 thread because the Google Cloud Monitoring exporter processes batches

"round"?

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core/src/test/java/google/registry/mosapi/MosApiMetricsTest.java line 40 at r1 (raw file):

import org.junit.jupiter.api.Test;
import org.mockito.ArgumentCaptor;

nit: link the class being tested in a class-level javadoc comment like we do for other test classes

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core/src/main/java/google/registry/config/RegistryConfig.java line 1472 at r1 (raw file):

    @Provides
    @Config("mosapiMetricsThreadCnt")

Use the full name Count, there's no point in saving only two letters when it's already this long

same for the config field too