主要分析的类
com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher
在sentinel监控数据db持久化中，更换了MetricController的存储实现，可以发现com.alibaba.csp.sentinel.dashboard.repository.metric.MetricsRepository原来只有com.alibaba.csp.sentinel.dashboard.repository.metric.repository.InMemoryMetricsRepository实现
从全局可知，用到MetricsRepository的类原有的也就只有
com.alibaba.csp.sentinel.dashboard.repository.metric.repository.InMemoryMetricsRepository 监控数据的内存实现
com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher 监控数据抓取器
com.alibaba.csp.sentinel.dashboard.controller.MetricController dashboard获取监控数据入口
可以猜测监控数据获取实现的地方是在com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher
还有一种方法不用猜的方式，在我们实现了dashboard的监控数据db存储后，发现
com.alibaba.csp.sentinel.dashboard.repository.metric.repository.SentinelMetricsRepository#saveAll
只要看哪里调用了存储的方法，就可以知道数据是怎么获取从而存储的。
com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher#writeMetric
com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher#fetchOnce
/**
* fetch metric between [startTime, endTime], both side inclusive
*/
private void fetchOnce(String app, long startTime, long endTime, int maxWaitSeconds) {
if (maxWaitSeconds <= 0) {
throw new IllegalArgumentException("maxWaitSeconds must > 0, but " + maxWaitSeconds);
}
//获取应用的基本信息
AppInfo appInfo = appManagement.getDetailApp(app);
// auto remove for app
if (appInfo.isDead()) {
logger.info("Dead app removed: {}", app);
appManagement.removeApp(app);
return;
}
//查看应用的机器信息（比如ip）
Set<MachineInfo> machines = appInfo.getMachines();
logger.debug("enter fetchOnce(" + app + "), machines.size()=" + machines.size()
+ ", time intervalMs [" + startTime + ", " + endTime + "]");
if (machines.isEmpty()) {
return;
}
final String msg = "fetch";
AtomicLong unhealthy = new AtomicLong();
final AtomicLong success = new AtomicLong();
final AtomicLong fail = new AtomicLong();
long start = System.currentTimeMillis();
/** app_resource_timeSecond -> metric */
final Map<String, MetricEntity> metricMap = new ConcurrentHashMap<>(16);
final CountDownLatch latch = new CountDownLatch(machines.size());
for (final MachineInfo machine : machines) {
// 机器不正常 auto remove
if (machine.isDead()) {
latch.countDown();
appManagement.getDetailApp(app).removeMachine(machine.getIp(), machine.getPort());
logger.info("Dead machine removed: {}:{} of {}", machine.getIp(), machine.getPort(), app);
continue;
}
if (!machine.isHealthy()) {
latch.countDown();
unhealthy.incrementAndGet();
continue;
}
//机器正常的情况下
final String url = "http://" + machine.getIp() + ":" + machine.getPort() + "/" + METRIC_URL_PATH
+ "?startTime=" + startTime + "&endTime=" + endTime + "&refetch=" + false;
final HttpGet httpGet = new HttpGet(url);
httpGet.setHeader(HTTP.CONN_DIRECTIVE, HTTP.CONN_CLOSE);
httpclient.execute(httpGet, new FutureCallback<HttpResponse>() {
@Override
public void completed(final HttpResponse response) {
try {
handleResponse(response, machine, metricMap);
success.incrementAndGet();
} catch (Exception e) {
logger.error(msg + " metric " + url + " error:", e);
} finally {
latch.countDown();
}
}
@Override
public void failed(final Exception ex) {
latch.countDown();
fail.incrementAndGet();
httpGet.abort();
if (ex instanceof SocketTimeoutException) {
logger.error("Failed to fetch metric from <{}>: socket timeout", url);
} else if (ex instanceof ConnectException) {
logger.error("Failed to fetch metric from <{}> (ConnectionException: {})", url, ex.getMessage());
} else {
logger.error(msg + " metric " + url + " error", ex);
}
}
@Override
public void cancelled() {
latch.countDown();
fail.incrementAndGet();
httpGet.abort();
}
});
}
try {
latch.await(maxWaitSeconds, TimeUnit.SECONDS);
} catch (Exception e) {
logger.info(msg + " metric, wait http client error:", e);
}
//long cost = System.currentTimeMillis() - start;
//logger.info("finished " + msg + " metric for " + app + ", time intervalMs [" + startTime + ", " + endTime
// + "], total machines=" + machines.size() + ", dead=" + dead + ", fetch success="
// + success + ", fetch fail=" + fail + ", time cost=" + cost + " ms");
writeMetric(metricMap);
}
final String url = "http://" + machine.getIp() + ":" + machine.getPort() + "/" + METRIC_URL_PATH
+ "?startTime=" + startTime + "&endTime=" + endTime + "&refetch=" + false;
final HttpGet httpGet = new HttpGet(url);
这里是调用机器的**“metric”**接口获取数据。
metric接口位于sentinel-transport【sentinel通信包】下
com.alibaba.csp.sentinel.command.handler.SendMetricCommandHandler
com.alibaba.csp.sentinel.node.metric.MetricSearcher
注释写的已经很清楚了，通过MetricSearcher查询机器的监控数据文件
com.alibaba.csp.sentinel.node.metric.MetricWriter#listMetricFiles
此方法是获取应用机器下的监控文件的。
知道了dashboard怎么获取的监控数据，那监控数据是怎么写到应用机器的磁盘？
com.alibaba.csp.sentinel.n`在这里插入代码片`ode.metric.MetricWriter#listMetricFiles
所属的类com.alibaba.csp.sentinel.node.metric.MetricWriter从命名就可以看出是写监控数据的。
com.alibaba.csp.sentinel.node.metric.MetricWriter#write
查看write方法的调用
com.alibaba.csp.sentinel.slots.block.flow.FlowRuleManager
在应用启动的时候FlowRuleManager会注册监听配置项的变化，同时也会注册MetricTimerListener，通过MetricTimerListener将监控数据写到应用所在的磁盘上，dashborad通过ip+port+方法名+参数调用获取应用磁盘上文件的监控数据。