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Export prometheus metrics directly from handler

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This commit is contained in:
Simon Detheridge 2021-06-22 16:40:18 +01:00
parent da8476b008
commit 1eb22a7d6d
1 changed files with 35 additions and 34 deletions
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69
services/git-bridge/src/main/java/uk/ac/ic/wlgitbridge/server/PrometheusHandler.java
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@ -1,6 +1,7 @@
package uk.ac.ic.wlgitbridge.server;
import io.prometheus.client.exporter.MetricsServlet;
import io.prometheus.client.CollectorRegistry;
import io.prometheus.client.exporter.common.TextFormat;
import io.prometheus.client.hotspot.DefaultExports;
import org.eclipse.jetty.server.HttpConnection;
@ -15,33 +16,18 @@ import uk.ac.ic.wlgitbridge.util.Log;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.Arrays;
/**
* Wrapper for the MetricsServlet from the Prometheus client.
*
* We wrap this in a handler here, as we use a wildcard servlet context on /*, and adding
* an additional servlet context collides with it. Adding a servlet context on /metrics
* causes a redirect to /metrics/ which breaks things when jetty doesn't know the full
* public URL.
*
* There may still be a better way to do this, but it works.
**/
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
public class PrometheusHandler extends AbstractHandler {
private final ServletHolder holder;
public PrometheusHandler() {
DefaultExports.initialize();
this.holder = new ServletHolder(new MetricsServlet());
try {
this.holder.initialize();
} catch (Exception e) {
Log.error("Unable to initialise metrics servlet: " + e.getMessage());
}
}
@Override
@ -58,20 +44,35 @@ public class PrometheusHandler extends AbstractHandler {
&& target.matches("^/metrics/?$")
) {
Log.info(method + " <- /metrics");
if (!this.holder.isAvailable()) {
try {
this.holder.start();
} catch (Exception e) {
Log.error("Unable to start metrics servlet: " + e.getMessage());
response.setStatus(500);
baseRequest.setHandled(true);
return;
}
}
this.holder.handle(baseRequest, request, response);
this.printMetrics(request, response);
baseRequest.setHandled(true);
}
}
private void printMetrics(
HttpServletRequest request,
HttpServletResponse response
) throws ServletException, IOException {
response.setStatus(200);
String contentType = TextFormat.chooseContentType(request.getHeader("Accept"));
response.setContentType(contentType);
Writer writer = new BufferedWriter(response.getWriter());
try {
TextFormat.writeFormat(contentType, writer, CollectorRegistry.defaultRegistry.filteredMetricFamilySamples(parse(request)));
writer.flush();
} finally {
writer.close();
}
}
private Set<String> parse(HttpServletRequest req) {
String[] includedParam = req.getParameterValues("name[]");
if (includedParam == null) {
return Collections.emptySet();
} else {
return new HashSet<String>(Arrays.asList(includedParam));
}
}
}