Add AggregateMetricReader able to aggregate counters and gauges

Different physical sources for the same logical metric just need to
publish them with a period-separated prefix, and this reader will
aggregate (by truncating the metric names, dropping the prefix).

Very useful (for instance) if multiple application instances are
feeding to a central (e.g. redis) repository and you want to
display the results. Useful in conjunction with a
MetricReaderPublicMetrics for hooking up to the /metrics endpoint.

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/aggregate/AggregateMetricReader.java

@@ -0,0 +1,142 @@
+/*
+ * Copyright 2014-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.boot.actuate.metrics.aggregate;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.springframework.boot.actuate.metrics.Metric;
+import org.springframework.boot.actuate.metrics.reader.MetricReader;
+import org.springframework.boot.actuate.metrics.repository.InMemoryMetricRepository;
+import org.springframework.util.StringUtils;
+
+/**
+ * A metric reader that aggregates values from a source reader, normally one that has been
+ * collecting data from many sources in the same form (like a scaled-out application). The
+ * source has metrics with names in the form <code>*.*.counter.**</code> and
+ * <code>*.*.[anything].**</code> (the length of the prefix is controlled by the
+ * {@link #setTruncateKeyLength(int) truncateKeyLength} property, and defaults to 2,
+ * meaning 2 period separated fields), and the result has metric names in the form
+ * <code>aggregate.count.**</code> and <code>aggregate.[anything].**</code>. Counters are
+ * summed and anything else (i.e. gauges) are aggregated by choosing the most recent
+ * value.
+ *
+ * @author Dave Syer
+ *
+ */
+public class AggregateMetricReader implements MetricReader {
+
+	private MetricReader source;
+
+	private int truncate = 2;
+
+	private String prefix = "aggregate.";
+
+	public AggregateMetricReader(MetricReader source) {
+		this.source = source;
+	}
+
+	/**
+	 * The number of period-separated keys to remove from the start of the input metric
+	 * names before aggregating.
+	 *
+	 * @param truncate length of source metric prefixes
+	 */
+	public void setTruncateKeyLength(int truncate) {
+		this.truncate = truncate;
+	}
+
+	/**
+	 * Prefix to apply to all output metrics. A period will be appended if no present in
+	 * the provided value.
+	 *
+	 * @param prefix the prefix to use default "aggregator.")
+	 */
+	public void setPrefix(String prefix) {
+		this.prefix = prefix.endsWith(".") ? prefix : prefix + ".";
+	}
+
+	@Override
+	public Metric<?> findOne(String metricName) {
+		if (!metricName.startsWith(this.prefix)) {
+			return null;
+		}
+		InMemoryMetricRepository result = new InMemoryMetricRepository();
+		String baseName = metricName.substring(this.prefix.length());
+		for (Metric<?> metric : this.source.findAll()) {
+			String name = getSourceKey(metric.getName());
+			if (baseName.equals(name)) {
+				update(result, name, metric);
+			}
+		}
+		return result.findOne(metricName);
+	}
+
+	@Override
+	public Iterable<Metric<?>> findAll() {
+		InMemoryMetricRepository result = new InMemoryMetricRepository();
+		for (Metric<?> metric : this.source.findAll()) {
+			String key = getSourceKey(metric.getName());
+			if (key != null) {
+				update(result, key, metric);
+			}
+		}
+		return result.findAll();
+	}
+
+	@Override
+	public long count() {
+		Set<String> names = new HashSet<String>();
+		for (Metric<?> metric : this.source.findAll()) {
+			String name = getSourceKey(metric.getName());
+			if (name != null) {
+				names.add(name);
+			}
+		}
+		return names.size();
+	}
+
+	private void update(InMemoryMetricRepository result, String key, Metric<?> metric) {
+		String name = this.prefix + key;
+		Metric<?> aggregate = result.findOne(name);
+		if (aggregate == null) {
+			aggregate = new Metric<Number>(name, metric.getValue(), metric.getTimestamp());
+		}
+		else if (key.startsWith("counter")) {
+			// accumulate all values
+			aggregate = new Metric<Number>(name, metric.increment(
+					aggregate.getValue().intValue()).getValue(), metric.getTimestamp());
+		}
+		else if (aggregate.getTimestamp().before(metric.getTimestamp())) {
+			// sort by timestamp and only take the latest
+			aggregate = new Metric<Number>(name, metric.getValue(), metric.getTimestamp());
+		}
+		result.set(aggregate);
+	}
+
+	private String getSourceKey(String name) {
+		String[] keys = StringUtils.delimitedListToStringArray(name, ".");
+		if (keys.length <= this.truncate) {
+			return null;
+		}
+		StringBuilder builder = new StringBuilder(keys[this.truncate]);
+		for (int i = this.truncate + 1; i < keys.length; i++) {
+			builder.append(".").append(keys[i]);
+		}
+		return builder.toString();
+	}
+
+}

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/aggregate/AggregateMetricReaderTests.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2012-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.metrics.aggregate;
+
+import java.util.Date;
+
+import org.junit.Test;
+import org.springframework.boot.actuate.metrics.Metric;
+import org.springframework.boot.actuate.metrics.repository.InMemoryMetricRepository;
+import org.springframework.boot.actuate.metrics.writer.Delta;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+/**
+ * @author Dave Syer
+ */
+public class AggregateMetricReaderTests {
+
+	private InMemoryMetricRepository source = new InMemoryMetricRepository();
+
+	private AggregateMetricReader reader = new AggregateMetricReader(this.source);
+
+	@Test
+	public void writeAndReadDefaults() {
+		this.source.set(new Metric<Double>("foo.bar.spam", 2.3));
+		assertEquals(2.3, this.reader.findOne("aggregate.spam").getValue());
+	}
+
+	@Test
+	public void writeAndReadLatestValue() {
+		this.source.set(new Metric<Double>("foo.bar.spam", 2.3, new Date(100L)));
+		this.source.set(new Metric<Double>("oof.rab.spam", 2.4, new Date(0L)));
+		assertEquals(2.3, this.reader.findOne("aggregate.spam").getValue());
+	}
+
+	@Test
+	public void writeAndReadExtraLong() {
+		this.source.set(new Metric<Double>("blee.foo.bar.spam", 2.3));
+		this.reader.setTruncateKeyLength(3);
+		assertEquals(2.3, this.reader.findOne("aggregate.spam").getValue());
+	}
+
+	@Test
+	public void onlyPrefixed() {
+		this.source.set(new Metric<Double>("foo.bar.spam", 2.3));
+		assertNull(this.reader.findOne("spam"));
+	}
+
+	@Test
+	public void incrementCounter() {
+		this.source.increment(new Delta<Long>("foo.bar.counter.spam", 2L));
+		this.source.increment(new Delta<Long>("oof.rab.counter.spam", 3L));
+		assertEquals(5L, this.reader.findOne("aggregate.counter.spam").getValue());
+	}
+
+	@Test
+	public void countGauges() {
+		this.source.set(new Metric<Double>("foo.bar.spam", 2.3));
+		this.source.set(new Metric<Double>("oof.rab.spam", 2.4));
+		assertEquals(1, this.reader.count());
+	}
+
+	@Test
+	public void countGaugesAndCounters() {
+		this.source.set(new Metric<Double>("foo.bar.spam", 2.3));
+		this.source.set(new Metric<Double>("oof.rab.spam", 2.4));
+		this.source.increment(new Delta<Long>("foo.bar.counter.spam", 2L));
+		this.source.increment(new Delta<Long>("oof.rab.counter.spam", 3L));
+		assertEquals(2, this.reader.count());
+	}
+
+}

spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -890,7 +890,7 @@ beans are gathered by the endpoint. You can easily change that by defining your
 
 
 [[production-ready-metric-repositories]]
-=== Performance
+=== Special features with Java 8
 
 The default implementation of `GaugeService` and `CounterService` provided by Spring Boot
 depends on the version of Java that you are using. With Java 8 (or better) the
@@ -944,10 +944,10 @@ Example:
 ----
 
 @Value("${spring.application.name:application}.${random.value:0000}")
-private String prefix = "metrics;
+private String prefix = "metrics";
 
 @Value("${metrics.key:METRICSKEY}")
-private String key = "KEY;
+private String key = "METRICSKEY";
 
 @Bean
 MetricWriter metricWriter() {
@@ -957,15 +957,51 @@ MetricWriter metricWriter() {
 
 
 
+[[production-ready-metric-aggregation]]
+=== Aggregating metrics from multiple sources
+There is an `AggregateMetricReader` that you can use to consolidate metrics from different
+physical sources. Sources for the same logical metric just need to publish them with a
+period-separated prefix, and the reader will aggregate (by truncating the metric names,
+and dropping the prefix). Counters are summed and everything else (i.e. gauges) take their
+most recent value.
+
+This is very useful (for instance) if multiple application instances are feeding to a
+central (e.g. redis) repository and you want to display the results. Particularly
+recommended in conjunction with a `MetricReaderPublicMetrics` for hooking up to the
+results to the "/metrics" endpoint. Example:
+
+[source,java,indent=0]
+----
+	@Bean
+	public PublicMetrics metricsAggregate() {
+		return new MetricReaderPublicMetrics(aggregates());
+	}
+
+	@Bean
+	protected MetricReader repository(RedisConnectionFactory connectionFactory) {
+		RedisMetricRepository repository = new RedisMetricRepository(connectionFactory,
+				"metrics", "METRICSKEY");
+		return repository;
+	}
+
+	@Bean
+	protected MetricReader aggregates() {
+		AggregateMetricReader repository = new AggregateMetricReader(repository());
+		return repository;
+	}
+----
+
+
+
 [[production-ready-dropwizard-metrics]]
 === Dropwizard Metrics
-Users of the https://dropwizard.github.io/metrics/[Dropwizard '`Metrics`' library] will
-automatically find that Spring Boot metrics are published to
-`com.codahale.metrics.MetricRegistry`. A default `com.codahale.metrics.MetricRegistry`
-Spring bean will be created when you declare a dependency to the
-`io.dropwizard.metrics:metrics-core` library; you can also register you own `@Bean`
-instance if you need customizations. Metrics from the `MetricRegistry` are also
-automatically exposed via the `/metrics` endpoint.
+A default `MetricRegistry` Spring bean will be created when you declare a dependency to
+the `io.dropwizard.metrics:metric-core` library; you can also register you own `@Bean`
+instance if you need customizations. Users of the
+https://dropwizard.github.io/metrics/[Dropwizard '`Metrics`' library] will find that
+Spring Boot metrics are automatically published to `com.codahale.metrics.MetricRegistry`.
+Metrics from the `MetricRegistry` are also automatically exposed via the `/metrics`
+endpoint
 
 When Dropwizard metrics are in use, the default `CounterService` and `GaugeService` are
 replaced with a `DropwizardMetricServices`, which is a wrapper around the `MetricRegistry`