Added prometheus monitoring.

pom.xml

@@ -31,6 +31,20 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-data-mongodb</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-actuator</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.prometheus</groupId>
+            <artifactId>simpleclient</artifactId>
+            <version>RELEASE</version>
+        </dependency>
+        <dependency>
+            <groupId>io.prometheus</groupId>
+            <artifactId>simpleclient_common</artifactId>
+            <version>RELEASE</version>
+        </dependency>
         <dependency>
             <groupId>org.springframework.data</groupId>
             <artifactId>spring-data-rest-hal-browser</artifactId>

src/main/java/works/weave/socks/shipping/configuration/PrometheusEndpointContextConfiguration.java

@@ -0,0 +1,40 @@
+package works.weave.socks.shipping.configuration;
+
+import io.prometheus.client.CollectorRegistry;
+import org.springframework.boot.actuate.autoconfigure.ExportMetricWriter;
+import org.springframework.boot.actuate.autoconfigure.ManagementContextConfiguration;
+import org.springframework.boot.actuate.condition.ConditionalOnEnabledEndpoint;
+import org.springframework.boot.actuate.metrics.writer.MetricWriter;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.context.annotation.Bean;
+import works.weave.socks.shipping.controllers.PrometheusEndpoint;
+import works.weave.socks.shipping.controllers.PrometheusMvcEndpoint;
+import works.weave.socks.shipping.monitoring.PrometheusMetricWriter;
+
+@ManagementContextConfiguration
+public class PrometheusEndpointContextConfiguration {
+
+    @Bean
+    public PrometheusEndpoint prometheusEndpoint(CollectorRegistry registry) {
+        return new PrometheusEndpoint(registry);
+    }
+
+    @Bean
+    @ConditionalOnBean(PrometheusEndpoint.class)
+    @ConditionalOnEnabledEndpoint("prometheus")
+    PrometheusMvcEndpoint prometheusMvcEndpoint(PrometheusEndpoint prometheusEndpoint) {
+        return new PrometheusMvcEndpoint(prometheusEndpoint);
+    }
+
+    @Bean
+    CollectorRegistry collectorRegistry() {
+        return new CollectorRegistry();
+    }
+
+    @Bean
+    @ExportMetricWriter
+    MetricWriter prometheusMetricWriter(CollectorRegistry registry) {
+        return new PrometheusMetricWriter(registry);
+    }
+
+}

src/main/java/works/weave/socks/shipping/controllers/PrometheusEndpoint.java

@@ -0,0 +1,30 @@
+package works.weave.socks.shipping.controllers;
+
+import io.prometheus.client.CollectorRegistry;
+import io.prometheus.client.exporter.common.TextFormat;
+import org.springframework.boot.actuate.endpoint.AbstractEndpoint;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.io.Writer;
+
+public class PrometheusEndpoint extends AbstractEndpoint<String> {
+
+    private CollectorRegistry registry;
+
+    public PrometheusEndpoint(CollectorRegistry registry) {
+        super("prometheus", false, true);
+        this.registry = registry;
+    }
+
+    @Override
+    public String invoke() {
+        Writer writer = new StringWriter();
+        try {
+            TextFormat.write004(writer, registry.metricFamilySamples());
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return writer.toString();
+    }
+}

src/main/java/works/weave/socks/shipping/controllers/PrometheusMvcEndpoint.java

@@ -0,0 +1,31 @@
+package works.weave.socks.shipping.controllers;
+
+import io.prometheus.client.exporter.common.TextFormat;
+import org.springframework.boot.actuate.endpoint.mvc.AbstractEndpointMvcAdapter;
+import org.springframework.boot.actuate.endpoint.mvc.HypermediaDisabled;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestMethod;
+import org.springframework.web.bind.annotation.ResponseBody;
+
+import java.util.Collections;
+
+public class PrometheusMvcEndpoint extends AbstractEndpointMvcAdapter<PrometheusEndpoint> {
+
+    public PrometheusMvcEndpoint(PrometheusEndpoint delegate) {
+        super(delegate);
+    }
+
+    @RequestMapping(method = RequestMethod.GET, produces = TextFormat.CONTENT_TYPE_004)
+    @ResponseBody
+    @HypermediaDisabled
+    protected Object invoke() {
+        if (!getDelegate().isEnabled()) {
+            return new ResponseEntity<>(
+                    Collections.singletonMap("message", "This endpoint is disabled"),
+                    HttpStatus.NOT_FOUND);
+        }
+        return super.invoke();
+    }
+}

src/main/java/works/weave/socks/shipping/monitoring/PrometheusMetricWriter.java

@@ -0,0 +1,54 @@
+package works.weave.socks.shipping.monitoring;
+
+import io.prometheus.client.CollectorRegistry;
+import io.prometheus.client.Counter;
+import io.prometheus.client.Gauge;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.actuate.metrics.Metric;
+import org.springframework.boot.actuate.metrics.writer.Delta;
+import org.springframework.boot.actuate.metrics.writer.MetricWriter;
+
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+public class PrometheusMetricWriter implements MetricWriter {
+
+    private final ConcurrentMap<String, Counter> counters = new ConcurrentHashMap<>();
+    private final ConcurrentMap<String, Gauge> gauges = new ConcurrentHashMap<>();
+    private CollectorRegistry registry;
+
+    @Autowired
+    public PrometheusMetricWriter(CollectorRegistry registry) {
+        this.registry = registry;
+    }
+
+    @Override
+    public void increment(Delta<?> delta) {
+        counter(delta.getName()).inc(delta.getValue().doubleValue());
+    }
+
+    @Override
+    public void reset(String metricName) {
+        counter(metricName).clear();
+    }
+
+    @Override
+    public void set(Metric<?> value) {
+        gauge(value.getName()).set(value.getValue().doubleValue());
+    }
+
+    private Counter counter(String name) {
+        String key = sanitizeName(name);
+        return counters.computeIfAbsent(key, k -> Counter.build().name(k).help(k).register(registry));
+    }
+
+    private Gauge gauge(String name) {
+        String key = sanitizeName(name);
+        return gauges.computeIfAbsent(key, k -> Gauge.build().name(k).help(k).register(registry));
+    }
+
+    private String sanitizeName(String name) {
+        return name.replaceAll("[^a-zA-Z0-9_]", "_");
+    }
+
+}